G5P Using chemicals safely
Using chemicals safely
G5p
June 2010
June 2010
The world is made from chemicals: the clouds, the sea,
the groceries in our supermarket trolley and even our
own bodies.
G5p Using chemicals safely
Contents
1 Introduction...................................................................................................................................... 2
1.1 Materials in the curriculum................................................................................................ 2
1.2 Safety when studying materials ........................................................................................ 2
1.3 Chemical hazard warning symbols ................................................................................... 3
2 Handling chemicals and looking after ourselves and the children when using them ....................... 4
2.1 Risk assessments when working with chemicals ............................................................. 4
2.2 Supervision of pupils and training for staff ........................................................................ 5
2.3 Storing chemicals ............................................................................................................. 6
2.4 Is protective clothing needed? .......................................................................................... 6
2.5 Safe sources of heat ........................................................................................................ 7
2.6 Heating and burning ......................................................................................................... 8
2.7 Clean conditions for tasting, eating and drinking activities ............................................... 9
2.8 Dealing with an accident .................................................................................................. 9
3 Chemical ideas: general advice and types of activity .................................................................... 12
3.1 Physical properties of materials ...................................................................................... 12
3.2 Natural and made ........................................................................................................... 13
3.3 The uses of materials ..................................................................................................... 13
3.4 Reversible and irreversible change ................................................................................ 13
3.5 Changing shape ............................................................................................................. 14
3.6 Changing with heating and cooling................................................................................. 14
3.7 Dissolving, a reversible change ...................................................................................... 16
3.8 Fermentation .................................................................................................................. 17
4 Chemicals for primary science: types and details of how to use them .......................................... 18
5 Chemical Index .............................................................................................................................. 72
Acknowledgements: we would like to thank Timstar Ltd for the loan of equipment and Matthew
Watson and Lynne Cole for reading the draft guide and offering valuable comments.
Strictly Confidential
Circulate to members and associates only
As with all CLEAPSS materials, members and associates are free to copy all or part of this guide for
use in their own establishments.
© CLEAPSS® 2010
CLEAPSS
The Gardiner Building
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UB8 3PQ
Tel: 01895 251496
Fax: 01895 814372
E-mail: science@cleapss.org.uk
Web site: www.cleapss.org.uk
G5P Using chemicals safely
The guide is structured like this:
1 Introduction
First we explain how important it is to study ‘Materials’ and where they fit into a primary science
curriculum.
2 Handling chemicals: how to look after ourselves and the children when using them
Next, we give advice on how to use and look after your chemicals safely. We talk about using them
with pupils, storing them, disposing of waste and being prepared to deal with the emergencies that
may happen (though not very often: exciting science carried out by teachers who know what they
are doing is usually very safe).
3 Chemical ideas: general advice and types of activity
Then we look at a range of types of activity. We suggest how you can carry these out effectively and
safely and suggest some activities you might carry out to study them. The advice is general: see
section 4 for examples.
4 Chemicals for primary science: types and details of how to use them
We look at a range of chemicals and some activities you might do with them. Here you can find
details of the activities we have suggested, including safety advice and some practical points.
5 Index
We finish with an index listing chemical names. We have included a number of chemicals you might
use, giving some of their alternative names to help you to identify unknown samples and find better
alternatives if appropriate. We have also included some chemicals you might find lurking in a
cupboard, to tell you how to dispose of them.
References in this guide
Where references to other sources of information are give, unless otherwise stated these
publications are from CLEAPSS and can be accessed via the CLEAPSS Primary resource on the
primary part of the web site. Log-in details are supplied annually in the spring term edition of the
Primary Science and Technology newsletter (PST).
1
1 Introduction
In this guide we show how you can use chemicals to support teaching and learning in science.
Primary teachers may be more used to the word materials than chemicals but since all materials are
made of chemicals the two words can be considered synonymous. Primary science work on
materials prepares the ground for the study of chemistry in secondary schools.
Everything, including living things and our bodies, is made from chemicals. We shall be looking at
materials from the point of view of their chemical properties and behaviour: What they are like and
how they might or might not change if they are heated, mixed or otherwise allowed to react.
In every day use, the word chemical nowadays is often given a somewhat negative connotation.
Apparently healthy foods are declared ‘free of chemicals’. This is nonsense; chemicals (materials,
substances, ‘stuff’) make up the universe. An orange is packed with more than thirty chemicals but it
is still a natural product. In fact, the nearest chemical warehouse to you is your local supermarket.
Every product on the shelves (and of course the shelves, building and staff) is made up of
chemicals. Some may be harmful, like bleach; others are enjoyable, like chocolate.
1.1 Materials in the curriculum
Primary children may first be introduced to chemicals under the topic of Materials and their
properties, which has featured in National and other curricula for many years.
The youngest children experience, name and begin to classify common materials. They learn that
different materials have different properties, and that we use materials on
the basis of their properties. For example transparent glass is used for
windows, and waterproof tiles for roofs. The photograph illustrates
materials chosen for their particular properties to make the various parts of
a building.
As their knowledge and understanding develops, children begin to explore
changes in materials, both physical, such as freezing and melting, and
chemical, such as in cooking.
Older children investigate properties of materials in more depth, including magnetic behaviour,
insulation and conduction (both thermal and electrical). They classify materials into solids, liquids
and gases. They experience reversible and irreversible changes. Finally, they discover how to
separate solids from liquids by filtration, dissolved solids by evaporation and the effects of some
microorganisms on materials.
1.2 Safety when studying materials
This guide provides an introduction to a wide range of kitchen and other chemicals that children may
encounter in their work on materials. Most are harmless in small quantities and their imaginative use
can encourage a real enthusiasm for chemistry.
Because some chemicals are harmful, it is common sense and good practice to forbid eating and
drinking in science lessons. However, when the study of materials involves making a food then there
is satisfaction in eating a safe product you have made. Good hygiene is essential and you must, of
course, be alert to children’s food allergies and perhaps conditions like diabetes.
2
Hazardous chemicals must be handled with care. Take the proper precautions and share these, and
the reasons for them, with the children. Invite their involvement in safety planning, sharing
responsibility for their own safety, and later for the safety of others.
This guide should be read in association with any advice from your employer (the local authority or
school governors, etc). Your school health and safety representative may also be able to offer
advice.
1.3 Chemical hazard warning symbols
Suppliers are required to label chemicals with hazard warning symbols where appropriate. The
symbols that you are most likely to come across are:
HARMFUL
IRRITANT
HIGHLY FLAMMABLE 1
DANGEROUS FOR THE
ENVIRONMENT
Other symbols that you may come across (and, indeed, you may occasionally wish to use chemicals
so-labelled) include:
CORROSIVE
OXIDISING
TOXIC / VERY TOXIC
EXPLOSIVE
Before planning any activities, make sure you understand fully the hazards and how you can
manage them. If necessary contact CLEAPSS for advice.
Over the next few years some new symbols will be introduced as the Global Harmonisation System
for hazardous chemicals is brought into force.
1
The symbol for EXTREMELY FLAMMABLE substances is identical but chemicals with this classification are unlikely
to be used in primary schools.
3
2 Handling chemicals and looking after ourselves and the children
when using them
In this chapter you will find advice on how to use and look after your chemicals safely. This includes
using them with pupils, storing them, disposing of waste and being prepared to deal with the
emergencies that may possibly happen (though not very often: exciting science carried out by
teachers who know what they are doing is usually safe!).
2.1 Risk assessments when working with chemicals
Before handling any hazardous materials or undertaking a hazardous activity you must consult a risk
assessment and follow any advice it contains. Your employer is required to provide risk
assessments and in science and technology your employer does this by making your school a
member of CLEAPSS, providing a copy of the ASE publication Be safe! 2, or often both. In general
there are few risks to using or investigating chemicals in primary science activities. Those hazards
you may come across are generally easily controlled with the measures identified by a risk
assessment.
Your employer’s risk assessments may not fit exactly your circumstances. In this case you should
use your professional knowledge and experience to make sensible adaptations to your planning so
that your safety arrangements are as effective as those in the risk assessment. For example, you
are doing an activity that requires heat to melt chocolate. The risk assessment might describe
melting in a saucepan on a cooker, which you do not have. You could use a kettle to boil some water
to make a hot water bath to put a container in. This may involve you carrying a kettle of boiled water
into or across the classroom and you will need to make safe arrangements for this so no one is at
risk of being scalded.
Engage children in risk assessment. Encourage them to:
•
Read and understand instructions and safety labels on containers.
•
Consider what might go wrong. When asked about the possible risks of dissolving jelly cubes,
one boy thoughtfully added ‘A wet jelly cube on the floor would be really slippery’.
•
Think of ways of minimising the risk to themselves and others.
The concentration of a chemical in a solution makes a huge difference its hazard level. Bleach from
a bottle, for example, may be CORROSIVE or at least IRRITANT; However Milton’s fluid which contains
the active ingredient in most bleaches [sodium chlorate(I) also known as sodium hypochlorite]
contains this chemical but very diluted, so it will be safe to sterilise babies’ bottles.
2
Be Safe! (3rd Edition) ISBN 086357324X, £10 (Members: £6.50) The Association for Science Education, College
Lane, Hatfield, Herts AL10 9AA; Telephone: 01707 283000; Web site: www.ase.org.uk/booksales; E-mail:
booksales@ase.org.uk. This comprehensive guide has been adopted as a basis for health and safety in school
science and technology by most employers. (New edition in preparation for 2011)
4
Points to consider, in assessing risks when you or your children are about to use a hazardous
material or undertake a hazardous activity:
•
Check that your employer (local authority or governing body) has not, for some reason, banned
the chemical or procedure. (There is nothing reasonable that is banned nationally in primary
schools).
•
Consult available guidance: eg this guide and/or Be Safe!
•
Using your professional expertise and common sense, plan, and then take, all reasonable steps
to reduce both the likelihood and the severity of a potential accident. This means:
•
−
Use the smallest amount and most dilute chemical that will fulfil your educational aims.
−
Reduce the number of children involved if supervision might be an issue, or bring in extra
supervision.
−
Consider the available space and layout of the room, in case this might restrict what you
can do or see.
−
Train the children if they need particular skills to handle the chemical or equipment.
−
Consider the mood of the children. You might consider rescheduling a hazardous activity
rather than carrying it out after a wet playtime, for example.
−
Do the activity as a demonstration rather than as a class practical.
−
Brief classroom assistants or other adults on possible hazards and how to deal with them.
If, after all that, the risk of a serious accident is high then do not go ahead.
2.2 Supervision of pupils and training for staff
The level of supervision of pupils needed will depend on the risk assessment. Consider:
•
How hazardous are the chemicals and processes?
•
How serious would it be if something went wrong?
•
How well-prepared are the pupils to handle the chemicals and equipment?
•
How well are the pupils able to follow instructions?
In this guide, we assume that ‘normal supervision’ means pupils will be supervised at the same level
as when they are doing other activities. For ‘close supervision’, one trained adult might be able to
supervise up to six pupils.
Remember to consider the risks before and after activities too. What are the chances of one or more
pupils excitedly, maybe surreptitiously, investigating chemicals and equipment set out for an activity
later during the day? After activities, supervise the children to ensure that they wash their hands
thoroughly and do not skip the process. Make sure that equipment and chemicals are left or
disposed of safely.
Before undertaking an activity, if you feel you do not have sufficient experience then you will need
training. This can often happen simply by asking a more-experienced colleague to work through the
activity with you.
5
2.3 Storing chemicals
•
Any chemical which is generally recognised as ‘not suitable’ should not be kept in school.
•
Quantities of other chemicals should be as small as possible.
•
Any chemicals carrying hazard symbols must be stored securely and be kept safely away
from children while in use.
•
Large quantities of HIGHLY FLAMMABLE materials should be kept in a locked flammables
cupboard but such quantities are not needed for primary science.
•
Label all chemicals, and do not decant them into other, unlabelled containers.
You can find a bit more on storing chemicals in the article on page 6 of PST 28 (Spring 2004). You
can find this in the Primary Resource.
2.4 Is protective clothing needed?
Protective clothing can mean an apron to help keep you clean and this may be a very good idea for
both the teacher and the children. An old shirt can be useful for protecting children’s clothes. If worn
then it should be made from cotton or a cotton mixture, rather than more flammable materials, not
too thin and not baggy. Sleeves should not be loose and it should be secured to avoid loose pieces
from dangling over the activity.
In terms of a risk assessment the only available protective devices that might be needed are eye
protection and safety gloves.
Eye Protection: It is unusual for a primary science activity to require eye protection. Ask firstly
whether such an activity is appropriate for primary schools.
Eye protection is of two sorts: that which is splash proof against liquids, which includes safety
goggles and face shields, and those safety spectacles that have only impact resistance and are
intended to stop solids or some less hazardous liquids from entering the eyes. Eye protection can be
a hazard in itself, if it fits badly or is scratched. Safety spectacles or face shields are available in
smaller sizes from primary suppliers. They should conform to European Standard EN166 F.
Safety goggles
Safety spectacles
Note that the goggles should fit snugly around the face, enclosing the eyes. Goggles might only be
required occasionally by teachers handling CORROSIVE or TOXIC liquids.
In the event that a chemical enters the eye:
Low-hazard chemicals: Wash the eye with gently-running water. If there are any continued signs of
distress, seek medical attention.
Hazardous chemicals: Immediately wash the eye with gently-running water for at least 10 minutes
and for much longer in the case of alkalis (see the List of chemicals). Hold back the eyelids to rinse
underneath. Contact lenses must be removed. If the first aider has concerns, send for an ambulance
(and, for alkalis, ensure irrigation is continued during the journey).
6
Safety gloves: Some published texts advise wearing protective gloves when using materials that
can irritate the skin. If the gloves are too large for the children, they can make them clumsy and
liable to have an accident. Some suppliers produce gloves in small sizes. Nitrile, good-quality
unpowdered latex and polythene are suitable unless individuals suffer from an allergy to the
material. ‘Surgeons’ gloves are usually made from nitrile or latex and may be supplied in various
colours. Thin polythene gloves are cheap and can be suitable for some applications such as
handling slime but are not available in really small sizes.
The heavy-duty gloves on the left are chemical-resistant. The nitrile and latex gloves in the centre are
available in small sizes. The thin polythene gloves on the right might make small hands more clumsy but
may be useful at times.
It is unlikely for pupils to need full chemical-resistant protection (gloves to British
European Standard BS EN420) but teachers handling CORROSIVE or TOXIC
chemicals may need a pair: Look out for this symbol on packs of some tough
washing-up or DIY gloves in the supermarket or hardware store.
2.5 Safe sources of heat
Hot water is an excellent source of heat for many activities. The temperature of hot water from a
classroom tap should be regulated and therefore not scald either staff or children. Water from a
kettle or water heater should be cooled before use to no more than 50 °C. Use a ‘spirit’ thermometer
or datalogger to test this (mercury thermometers are not suitable for use in primary schools). Take
care to avoid splashing water on the skin, even at this temperature. Hot water should be dispensed
carefully by the teacher or teaching assistant.
Tealights (previously called nightlights) can be used but
should be placed securely in a metal tray, eg, a baking
tray or tin lid filled with sand. Stands made from bent
metal with a shelf to hold a foil dish above the flame are
available from some school suppliers. They too should be
used within a sand tray.
Hot-water bottles and other heating pads make an excellent,
non-splashy source of controlled heat that can last for a fairly
long time. Check the temperature by holding the thermometer or
datalogger probe close to the surface.
The heat pad in the picture has been covered with aluminium
foil to keep it clean. You can find more information on heating
with these devices in the article Heating with hot-water bottles
and hot packs on page 7 of PST 42 (autumn 2008). This is in
the Primary Resource.
Mains electric rings: stoves like the Baby Belling may already be used for cookery. If you use one,
follow the same strict safety precautions as for cooking activities.
7
Hairdryers are occasionally useful. Do not bring a hairdryer in from home because it may not have
been constructed to the same standards as those intended for use in schools. Hairdryers available
from school suppliers will have been thoroughly tested beyond the requirements for domestic
hairdryers. Supervise their use carefully and keep them away from water or becoming wet.
! Spirit burners, picnic stoves and other bottled gas devices, hot-air paint strippers and Bunsen
burners are not recommended for primary school use.
2.6 Heating and burning
When strong heating is required, materials can be heated or burned over tealight
flames in a metal lid (make sure there is no plastic or other lining) or in a metal
spoon. Remember that the lid or the spoon handle will get hot. The chemical sample
and lids can be held in a holder. One type is shaped like a wooden clothes peg
fixed to a handle made from square-section timber; another is made from
springy bent stainless steel wire. These are available from scientific
suppliers. Pliers are a possible substitute but remember that the
handles will get hot eventually.
Test-tube
holders
A sand tray
Safety with heating and burning
! Warn children about the hazards involved in the activity, especially that (for example)
hotplates may be hot without appearing so.
•
Close supervision is essential. In practice, one adult can only closely supervise six
children. That adult must give the children undivided attention; they must be well
briefed on safety, and should not be open to interruption by other children.
•
Warn children not to lean across the table in case they come into contact with the
flame or a hot object, or knock equipment over.
•
Combustible materials, including paper, should be moved away and no HIGHLY
FLAMMABLE materials should be in the room.
•
Light the tealights for the children, dispose of matches carefully and never leave
flames unattended.
•
Long hair and loose clothing should be tied back.
•
Do not allow lit candles to be carried around.
•
Children should stand for the activity, which makes it easier to move quickly if there is
an accident.
•
Never burn materials that may give off harmful fumes, eg, many plastics and fibres.
Pupils should not heat HIGHLY FLAMMABLE substances.
8
2.7 Clean conditions for tasting, eating and drinking activities
Before carrying out tasting, cooking, drinking or eating activities, make sure that all surfaces and
equipment and everybody’s hands are thoroughly clean. Soap and water used properly, followed by
thorough drying is appropriate for hands; pupils may need supervision. Normal washing-up is
appropriate for equipment: use dedicated cooking utensils or disposable ones. Surfaces can be
cleaned with warm soapy water and note that some contaminants need a good rub with a cloth to
remove them. Use ingredients stored for food use only or buy them fresh.
It is sometimes a good idea to disinfect work surfaces after they have been cleaned, particularly if
the surfaces have been contaminated with soil or animals. Surfaces that are old and very pitted will
have crevices that might harbour microorganisms and can only be dealt with using a disinfectant.
Bleaches, proprietary disinfectants or antiseptics can be diluted as directed and used to disinfect
surfaces. All disinfectants need to be in contact with the surface for some time to enable them to
work effectively. For diluted bleach and Milton, this could be as long as 30 minutes. It is important to
make sure the surface is really clean before treating it. Avoid splashing the eyes and wear gloves to
protect sensitive skins. Some products may stain surfaces, particularly if in contact for long periods:
check the label for this and other information.
Note also that most of these products lose activity over time, especially when diluted. Therefore,
always use freshly-made disinfectant solution.
Pupils could use very diluted disinfectant solutions for wiping surfaces before cooking activities. Do
not use disinfectants with children who may try drinking it.
2.8 Dealing with an accident
Planning for a safe activity
It is worth reading safety guidance before carrying out any practical work. Working with chemicals
raises the (remote) possibility of an accident and how to deal with such an event is given in the table
on page 11: Immediate action for an injury involving chemicals. You should be familiar with them
before an accident happens. Some schools make an enlarged copy of the list, laminate it and
display it on a notice board or near the sink.
It is helpful if pupils are taught how to behave if something goes wrong. Involve them by discussing
how they could react responsibly and remind them periodically to help them remember. Think about
the layout of the room when planning activities, so it is not difficult to reach pupils and deal with an
incident.
Spills
Dry spills can usually be swept up, wrapped and placed in the normal refuse, but check the chemical
details for hazardous materials. Most wet spills can be mopped up quickly with paper towels, cloths
or a mop, then diluted further in water and poured away, preferably down a toilet whose outlet goes
directly into the drainage system.
Oily spills may need detergent (washing-up liquid) to disperse them and allow them to be poured
away. Use quite a lot; perhaps a quantity equal to the spill.
9
Fire
Follow school instructions, making sure not to put yourself at risk.
•
In the event that a child’s hair catches fire: smother with a cloth then treat for burns.
•
In the event that a child’s clothing catches fire: Stop, drop and roll. This means stop the
casualty moving around and make her/him lie down on the floor. Then either roll the casualty
to smother the flames or, with the flames on top, cover with a fire blanket, thick cloth or coat,
whatever is close to hand, then treat for burns.
Dealing with an injury involving chemicals
Your school will have a first aid policy with first aiders, first aid kits and procedures. Follow these
procedures. For accidents involving chemicals on the skin, in the mouth or eye:
•
Establish what has been eaten or splashed. Check its hazards on the label of the original
container or look in the chemical index (section 5).
•
If first aid or medical assistance is needed, hand over the bottle or details from it so that the
first aider, paramedic or doctor knows what is involved.
! Have a supply of clean water available whenever work is carried out that may result in burns or
injuries to the eyes. Water directly from a tap is best; if not available, a clean jug and a bucket or
bowl of fresh, clean cold water may suffice.
10
Immediate action for an injury involving chemicals
Type of
injury
Burns
What to do
Cool under gently running water for 10 minutes or until heat is no longer felt. Call
for first aid if there are any concerns.
Chemicals in Low hazard chemicals: Rinse out the mouth. If any is swallowed and there are any
the mouth,
continued signs of distress, seek medical attention.
perhaps
Hazardous chemicals: Do no more than wash out the casualty’s mouth Sips of
swallowed
water may help cool the throat and help keep the airway open. If, after any first aid
treatment, the casualty needs further medical attention, send the container
including its label for identification with the casualty. If CORROSIVE or TOXIC: seek
immediate medical attention.
Chemicals
on clothes
If the chemical is at all FLAMMABLE, extinguish all flames in the area. Remove
contaminated clothing immediately and wash the contaminated area.
Ventilate the area of the spill. If necessary, take contaminated clothing
outside. Take particular care to wash out any spilled OXIDISING agents
thoroughly.
Inhaled
chemicals
Some chemicals may pose a risk of solvent abuse. If a child appears to be affected
by the chemical, sit her/him in uncontaminated air, avoiding the risk of chilling and
ensure that s/he takes plenty of deep breaths. If there are any continued signs of ill
effect, seek medical attention. For CORROSIVE or TOXIC chemicals, treat as above
and seek immediate medical attention if more than a sniff is inhaled.
Splashes in
the eye
Low-hazard chemicals: Wash the eye with gently-running water. If there are any
continued signs of distress, seek medical attention.
Hazardous chemicals: Immediately wash the eye with gently-running water for at
least 10 minutes, and for much longer in the case of alkalis (see the List of
chemicals). Hold back the eyelids to rinse underneath. Contact lenses must be
removed. If the first aider has any concerns, send for an ambulance (and, for
alkalis, ensure irrigation is continued during the journey).
Splashes on
skin
Low-hazard chemicals: Wash off with plenty of water. If there are any continued
signs of distress, seek medical attention.
Hazardous chemicals: Brush off any solids. Wash the skin for at least 5 minutes
(20 minutes if CORROSIVE) or until all traces of the chemical have disappeared.
Remove clothing as necessary. If the chemical adheres to the skin, wash gently
with soap. If there are any continued signs of distress or any signs of blistering,
seek medical attention; if CORROSIVE or TOXIC, seek immediate medical attention.
In the event of any other accident follow normal school procedures.
11
3 Chemical ideas: general advice and types of activity
In this section we look at a range of types of activity. We suggest how you can carry these out
effectively and safely, and suggest some activities you might carry out with materials. At the end of
each section there is a pink box in which we list a few types of chemicals that may be useful for the
type of activity. You can find fuller details of the activities by looking up the entry for that type of
chemical in chapter 4. We also suggest further CLEAPSS references for more information for your
use: see the blue boxes.
3.1 Physical properties of materials
Recognising and describing the properties, characteristics or nature of different materials is
fundamental to later work on materials. When children understand how materials vary, they can go
on to consider their everyday applications and why and how new materials can be made. It is
important to note that colour is not a good criterion for grouping or sorting materials, as many
materials can be made in a range of different colours.
Some properties are obvious. For example glass is transparent and wood is generally hard. Other
properties are not immediately apparent. When heated, glass will melt but wood chars and burns.
Once basic properties have been experienced, the more challenging properties can be introduced,
such as ability to float or being magnetic.
We have not included ‘smart materials’ in this guide. These challenge our conceptions of the
properties of materials and make fascinating follow-up or science club activities. Examples include
sheets that change colour with temperature changes and granules that fluff up to make puffs of
‘instant snow’ when they are added to water. Many are available from scientific suppliers 3.
Did you know?
Younger children can confuse an object and the material. They may confuse table with wood, for
example. They also need to experience anomalies. Most wood is hard and resistant but balsa is
neither although, interestingly, it is classified as a hardwood.
Simple work: exhibitions of samples of,
eg, different plastics including fabrics,
metals, ceramics, wax, water, cooking oil.
Further references on physical properties
More advanced work: Properties of
materials: see Plastics; magnetism: see
Metals; Conduction of heat and electricity:
see Metals and also polystyrene as an
insulator under Plastics, Floating and
sinking: see Cooking oils and fats, Metals
and Acids; Strength of materials: see
Cement and concrete.
PST 24 6 Modelling Sound
3
PST 19 4-5 Material Evidence? 2
PST 30 3-4 A key issue
Middlesex University Teaching Resources (MUTR: www.mutr.co.uk) supplies a lot of smart materials and publications with
information on them. Although aimed at secondary, they give good background information.
12
3.2 Natural and made
This can be a confusing topic for children who may be confused by a ‘made’ (also called ‘manmade’, artificial or synthetic) object formed from a ‘natural’ material. A wool sweater is one such
example: natural materials can be shaped and treated to change them, sometimes beyond
recognition. Confusingly, it is also possible to imitate natural materials, eg, wood or leather in plastic.
Nevertheless, some materials, eg, stone and wool are natural in origin, while others, eg, plastic and
synthetic fibres are made.
Examples of natural materials include
clay, metals and soils.
Further reference on natural / made materials
PST 19 4-5 Material Evidence?
Examples of made materials include
ceramics made from clay, plaster of
Paris, plastics and oils, waxes and
chemicals derived from oils.
3.3 The uses of materials
Most materials are chosen for use on the basis of their properties. These can also include aesthetic
qualities, which offers a link to Art and Design.
Choosing the right material for a task on the basis of its properties is an important skill. Modern
chemistry introduces designer materials, devised and made to meet a need.
Did you know!
Many materials have traditional uses that make use of specific properties. Transparent glass for
windows and waterproof rubber to make boots. Modern alternatives may combine these with
materials that have other useful properties, such as unbreakability or lightness. Different plastics,
metal alloys and microfibre fabrics have been developed to combine specific properties for particular
uses.
Unusual exceptions include a corrugated-cardboard chair and a stainless-steel wedding dress,
which are among the exhibits in the Science Museum in London.
See Clay and modelling materials,
Metals, Plaster of Paris and Oils, waxes
and chemicals derived from oils.
Further references on uses of materials
PST 22 3 That sinking feeling
PST 40 2-3 Hands-on materials
3.4 Reversible and irreversible change
In a physical change no new products are made. Thus, applying a force to squash or stretch
something is a physical change. So are freezing and melting, evaporating and condensing; the
material changes but the change is often not permanent and can be reversed. Chemical changes
result in a new product, eg, a baked cake, yoghurt, rust or a clay pot, and these changes cannot be
reversed, they are irreversible.
Some physical changes are not reversible. Cutting a branch from a tree is an irreversible physical
change but note that the branch still has the same physical and chemical properties even if its shape
has changed.
13
Mixing water and sand, is a reversible change. It can be reversed by filtering. Mixing water with
plaster of Paris is an irreversible change because new materials are made.
Everyday examples of permanent (irreversible) chemical change include:
•
All cooking such as making dough, baking bread, toasting bread, frying eggs, cooking vegetables;
firing clay to make pottery.
•
All burning including wood, wax candles, natural gas, petrol and other fuels, natural and made
fibres, plastics. Lighting fireworks also involves chemical change.
3.5 Changing shape
Many materials change shape in response to forces like stretching and bending. Materials like clay
stay in the new shape. Other materials like rubber return to their original shape (up to a point - if you
stretch rubber and some plastics beyond their elastic limit, they will be permanently deformed).
Examples of substances that can be used
to investigate change of shape: clay, wax,
plaster of Paris.
Further references on Changing shape
PST 18 4-5 and 19 4-5 Material Evidence
3.6 Changing with heating and cooling
Many materials change with temperature. They may melt, boil, dry out, char or burn. Some of these
changes are reversible but others are permanent (irreversible). What happens to them may also
depend on how strongly they are heated.
Temperature-related changes are easily shown with water, which can exist in all three ‘states’, solid,
liquid and gas within a manageable temperature range. Generally, solids melt to liquids; liquids
evaporate to gas; gases condense to liquids and liquids freeze or solidify to solids.
Some changes brought about by heating and cooling may appear reversible but if you look closely
there are some slight differences between what you started with and what is left at the end. Warming
butter ‘clarifies’ it; melting chocolate drives off some water and changes it very slightly.
Liquids will evaporate at temperatures that are below their boiling point. A puddle doesn’t need to
reach 100 °C to evaporate. A combination of warmth and the wind enables water particles to escape
from the surface of liquid water. The warmer and the windier, the faster the process, although if there
is high humidity (the air is already heavy with water vapour) evaporation will be slowed.
Similarly, water vapour in the air will condense at any temperature between 0 °C, below which it will
freeze, and 100 °C above which it will exist as a gas. Vapour will condense and collect on cold
surfaces, eg, windows.
14
Did you know!
The word ‘vapour’ is sometimes used to describe ‘gases’. Strictly, a gas is a material above its boiling
point, and ‘clouds of steam’ are water vapour (droplets of water). True ‘water gas’ is invisible boiling
stuff near the spout of a kettle. But at primary level, the word ‘gas’ can be used to cover the
apparently gaseous form of any material.
The temperature of a liquid does not rise higher than its boiling point. For example, if you carry on
heating boiling water its temperature remains 100 °C. The extra heat is used to allow its particles to
‘escape’ and turn into vapour particles.
A pure substance melts at distinct temperature, eg, ice melts at 0 °C, salt at 801 °C, sugar at 184 °C
and iron at 1539 °C. Chocolate and butter are not single pure substances, so neither melts at a single
given temperature (although part of the appeal of chocolate is that it melts around body temperature,
giving it its special ‘mouth feel’).
Pure substances also boil at distinct temperatures in normal circumstances, eg, water at 100 °C and
ethanol at 78 °C. Milk is not a pure substance and boils over a range of temperatures.
For melting and freezing see Oils, waxes
and chemicals derived from oils (c) Wax;
for evaporation see Salts and Sugars and
sweeteners.
Further references on heating
PST 33 2 Melting chocolate
PST 42 6 A burning candle
PST 45 6-7 Evaporting, melting and dissolving
PST 46 Evaporating, condensing and boiling
The table on the next page gives the effects of heat on some different substances. See sections 2.4
Safe sources of heat and 2.5 Safety when burning before trying any of them yourself.
15
Heating Common Substances
Substance
Initial heating
Further heating / burning
Bread (mixture)
Loses moisture; new materials
formed.
Chars and burns; new materials
formed.
Butter
Softens then melts, losing some
water.
Smokes, chars and may burn.
Chocolate (mixture)
Melts over a range of
temperatures; may lose a little
water.
Loses more water, decomposes
and chars; new materials formed.
Dough (mixture)
Loses some moisture;
decomposes giving off carbon
dioxide; new materials formed.
Burns; new materials formed.
Ice (pure substance)
Melts at a distinct temperature.
Vaporises at a distinct
temperature.
Lava (a mixture; can’t be done in
school!)
Melts.
Becomes runnier.
Metals (some are pure; can’t be
done in primary schools)
Depends on the metal. Iron
would become more bendy.
Pure metals melt at characteristic
temperatures.
Natural gas (a mixture)
Burns if ignited.
Burns with a blue flame.
Salt solution
Water evaporates.
Eventually dry salt left behind.
Soft clay (mixture)
Loses some moisture.
Loses all moisture; new materials
formed.
Sugar (pure substance)
Decomposes as it melts; new
materials formed.
Burns; new materials formed.
Thermoplastics
(including hot-melt glue)*
Melts.
Burns; new materials formed.
Wax (usually a mixture)
Melts.
Vaporises and the vapour burns.
Wood
Loses some moisture.
Chars and burns; new materials
formed.
* Take care with heating plastics. See Plastics in section 4 for safety advice.
3.7 Dissolving, a reversible change
Dissolving involves two substances, something to dissolve, the solute, eg, salt, and a liquid to
dissolve it in, the solvent, eg, water. Heat is not essential but it speeds up dissolving and increases
the amount that can dissolve. Cooling does not separate salt and water but the water can be
evaporated, leaving the salt. If you wish to regain the water, you need to allow the water vapour to
condense and collect it.
There are solvents other than water, such as alcohol (methylated spirits). Some are quite hazardous,
and only the safest alternatives should be used with pupils. Some materials, eg, ground coffee and
powder paint partially dissolve in water.
Many materials do not dissolve in water. Insoluble substances like sand, gravel or chalk can be
separated from water by sieving or filtering. The difference between a sieve and a filter is the size of
the mesh. Both make use of the same process: the liquid passes through a mesh and the solid does
not. Sieves are useful for large objects such as marbles or beads, filters for smaller particles like
sand because of their smaller mesh size. Children need to learn that it is logical to separate the
larger objects before the smaller particles in (say) a mixture of sand and marbles.
When a solvent (eg, water) cannot dissolve any more solid (eg, salt), the solution is saturated.
16
Did you know!
The difference between dissolving and melting can be hard to grasp. Sugar, for example, with a
melting point of 184 °C, dissolves in warm water without melting. But a jelly cube, which melts well
below the boiling point of water, both melts and dissolves in hot water.
Saturated solutions can be used to grow crystals. A number of chemicals give large crystals, but
follow the safety advice given in this guide. Impeccable cleanliness is necessary for large crystals;
every drop of dust ‘seeds’ a crystal.
When an insoluble substance doesn’t settle out from a solvent it may be called a suspension. The
mixture might look homogeneous (the same throughout, like milk) rather than inhomogeneous
(cloudy, as in ‘cloudy’ apple juice) but not transparent.
For dissolving versus melting see Food
additives; for evaporation see Salts and
Sugars and sweeteners. For insoluble
materials see Baking chemicals (Flour)
and Cooking oil.
Further references on dissolving
PST 8 4-5 Dissolving
PST 9 4-5 Dissolving and melting
PST 11 7 Letters about Dissolving and melting
PST 16 4-5 All mixed up - gases, liquids, solids . . .
and colloids
PST 31 2 Crystals - grow your own
3.8 Fermentation
Fermentation involves using microorganisms, such as yeast, to carry out chemical reactions.
Yeast acts on sugar, producing carbon dioxide gas, which causes bread to rise and ginger beer to
fizz. The gas exerts pressure, so fermentation must not take place in closed containers. Alcohol is
also produced during fermentation with yeast. While it is desirable in beer and wine (neither of which
have a place in primary school) be aware that tiny amounts are
present in real ginger beer. Many soft-drink versions are
carbonated artificially by pumping carbon dioxide into the drink and
do not contain alcohol. The heat used in baking bread evaporates
the alcohol from the dough.
Yoghurt is made using special bacteria that are beneficial to our
digestive systems.
For bread making see Alcohol.
Further references on fermentation
L190 Studying microorganisms in primary schools
PST 29 4-5 But are they all germs
17
4 Chemicals for primary science:
types and details of how to use them
The bulk of this section is organised alphabetically by chemical or topic according to the following
list. For each entry you will find information on the science, safety, storage, use, disposal and some
activities with model risk assessments.
Chemical or topic in this section
Chemical or topic
Other chemicals / substances included
Acids
Cola, lemon juice and other fruit juices, vinegar, citric acid,
ethanoic acid, salad dressings and other foods.
Alcohols and other solvents
Surgical spirit, tincture of iodine, duplicating fluid, after-shave
lotion, IDA, (yeast), propanone (nail varnish remover).
Baking chemicals
Bicarbonate of soda, baking powders, self-raising flour, sherbet
types of flour, instant puddings, baked goods and bath salts.
Balloon gas (Helium)
-
Calcium carbonate
Limestone, marble, chalk; some blackboard chalks.
Cement and concrete
-
Clay and modelling materials
-
Cooking oils and fats
Animal and vegetable oils, butter, dressings, beeswax, other
foods.
Food additives
Glycerine, gelatine, Vitamin C, food colours.
Glues
Solvent-based glues, balsa cement, wallpaper pastes,
superglues, low-temperature glue guns.
Metals
Brass, iron, copper, zinc, iron filings, mercury.
Oils, waxes, and chemicals
derived from oil
North Sea Gas, lighter fuel etc, petrol, paraffin, white spirit,
turpentine, oils, lubricating oil, engine oil, petroleum jelly
(Vaseline), tar, bitumen, wax, candles, tea lights.
Plaster of Paris
Modroc, calcium sulfate.
Plastics
Polystyrene, polythene, polypropylene, perspex, nylon.
Salts
Sodium chloride, Epsom salts, cream of Tartar, waterglass.
Soaps and cleaning products
Soaps, detergents, bleaches, disinfectants, antiseptics,
antibacterials.
Sugar and sweeteners
Sugar, sweeteners, other additives, milk, other beverages.
Soils and gardening products
Compost, potting composts, John Innes, fertilisers, plant foods,
loam.
18
You can also search for an activity or topic using the Activities List below or the references in
section 3. The Chemicals Index (section 5) lists individual chemicals.
Activities List
Topic or activity
Some activities and where to find them
Acids and alkalis
In addition to activities under Acids: cola, lemon juice and vinegar and Baking
chemicals, see also:
Calcium carbonate: chalk and marble: Use calcium carbonate to demonstrate
weathering or tooth decay.
Metals: Use metals to demonstrate that they react with acids.
Baking powders
Baking chemicals: Try baking scones with different proportions of acid and
alkali.
Balloon races
Balloon gas: Use helium for balloon races in work on gases.
Bath bombs
Baking chemicals: Use bicarbonate of soda to make bath bombs.
Bread making
See activities under Alcohol and other solvents and Baking chemicals.
Bubbles, stronger
Food additives: Use glycerine to make stronger, longer-lasting bubbles.
Burning irreversible change
Oils, waxes and chemicals derived from oil: Use wax to demonstrate burning
and irreversible change.
Candles, making
Oils, waxes and chemicals derived from oil: Making candles and exploring
variables.
Candles: tealights as a
Oils, waxes and chemicals derived from oil: Use well-secured tea lights as a
source of heat
source of heat.
Casting
Plaster of Paris: Use plaster of Paris for casting.
Chemical change
In addition to many examples, see Rusting, Plaster of Paris: Use plaster of
Paris to demonstrate permanent change.
Chemical change, edible
See Bread making and Scones.
Cleaning with solvents
Oils, waxes and chemicals derived from oil: Cleaning oily stains and spills.
Comparing different
Soil and gardening products: Use them for comparisons of different soils.
soils
Conduction of heat and
Metals: Use metals to demonstrate electrical and thermal conductivity.
electricity
Plastics: Use polystyrene to demonstrate thermal insulation.
Convection currents
See Dissolving, diffusion and convection currents.
Cooking
Metals: Use aluminium foil for cooking and heating activities.
See also Bread making and Scones.
Crystals, big
Sugars and sweeteners: Use sugar to make big crystals.
Crystals, making
Salts: Use salts to make crystals by dissolving and evaporation.
Density
See Floating and sinking (density).
Detergents
See activities under Soap and cleaning products.
Diffusion
See Dissolving, diffusion and convection currents.
Dissolving
Baking chemicals: Use flour as an example of an insoluble solid.
Sugars and sweeteners: Use sugars to demonstrate and investigate solutions.
Sugars and sweeteners: Use tea to demonstrate that not all solutions are
colourless.
See also Solutions.
19
Dissolving, alternative
Propanone: Use nail-varnish remover to demonstrate dissolving as an
solvent
alternative solvent to water.
Dissolving vs melting
Food additives: Use gelatine to demonstrate melting and dissolving.
Dissolving, diffusion and
convection currents
Food additives: Use food colouring to make water easier to see, eg,
comparing cold and hot water.
Double refraction
Calcium carbonate: chalk and marble: Demonstrate double refraction in calcite.
in calcite
Drainage speed
See Soil, types.
Electrical and thermal
conductivity
See Conduction of heat and electricity.
Electricity from
Acids: cola, lemon juice and vinegar: Make electricity from fruit.
chemicals
Electromagnets
Metals: Use iron rods to make electromagnets.
Evaporation
Alcohols and other solvents: Use surgical spirit or hand-rubs to demonstrate
evaporation.
Salts: Use salts to make crystals by dissolving and evaporation.
Sugars and sweeteners: Use drinks as examples of impure liquids.
Fats in foods
Cooking oils and fats: Use cooking oils to demonstrate fats in foods.
Fertiliser
See Plant growth.
Fire extinguisher
Baking chemicals: Use bicarbonate of soda to demonstrate carbon dioxide gas
as a fire extinguisher.
Floating and sinking
Cooking oils and fats: Using cooking oil to demonstrate that oil floats on water
(density)
and the effect of emulsifiers.
Metals: Use metals for floating and sinking activities (density activities).
Acids: cola, lemon juice and vinegar: Use cola as a challenging example of
floating and sinking.
Friction
See Lubrication.
Healthy eating examples
Food additives: Use foods containing vitamin C as examples of healthy eating.
Heat conduction
See Conduction of heat and electricity.
and insulation
Heat, effect on materials
Plastics: Test the effect of heat on materials.
Oils, waxes and chemicals derived from oil: Use wax to explore the effect of
(moderate) heat on materials, a physical change.
Oils, waxes and chemicals derived from oil: Use wax to demonstrate burning
and irreversible change.
See also Dissolving, diffusion and convection currents.
Heating
Metals: Use aluminium foil for cooking and heating activities.
Heating source
Oils, waxes and chemicals derived from oil: Use well-secured tea lights as a
source of heat.
Indicators
See Acids and alkalis.
Insoluble solids
See Dissolving.
Insulation
See Conduction of heat and electricity.
Irreversible change
See Reversible and irreversible changes.
20
King Kong's Hand
Baking chemicals: Use bicarbonate of soda to inflate balloons and kitchen
gloves with carbon dioxide gas.
Liquid, thick (viscous)
Food additives: Use glycerine to demonstrate a thick liquid.
Liquids
(different from water)
See Alcohols and other solvents, Cooking oils and fats and Oils, waxes and
chemicals derived from oil.
Liquids, impure
See Evaporation.
Lubrication
Cooking oils and fats: Use beeswax to reduce friction by lubrication.
Lubrication
Oils, waxes and chemicals derived from oil: Use petroleum products for
lubrication.
Magnetic fields,
See activities under Metals.
magnetism
Melting
Oils, waxes and chemicals derived from oil: Use wax to demonstrate the effect
of (moderate) heat on materials, a physical change.
Melting vs dissolving
Food additives: Use gelatine to demonstrate melting and dissolving.
Mirrors for light and
Metals: Use aluminium to make mirrors.
reflection
Mixtures, interesting
Soap and cleaning products: Use shaving foam or hair mousse to demonstrate
interesting mixtures.
Model making
In addition to activities under Glues see also
Plaster of Paris: Use plaster of Paris for sheet-modelling landscapes, etc.
Plastics: Use expanded polystyrene for modelling.
Neutralisation
See activities under Acids and Baking chemicals.
Newtonian materials
Baking chemicals: Use cornflour to make a non-Newtonian material.
Observation, burning
candle
In addition to being integral to many activities see Oils, waxes and chemicals
derived from oil: Observe the burning of a tea light closely.
Paints, oil-based
Oils, waxes and chemicals derived from oil: Using oil-based paints.
Papier mache
See Model making.
for modelling
Permanent change
See Reversible and irreversible changes.
pH (acidity/alkalinity)
Baking chemicals: Use bicarbonate of soda to demonstrate pH.
Plant growth
Soil and gardening products: Use fertiliser to show that plants need traces of
chemicals for healthy growth.
Plaster of Paris
See Model making.
Properties of materials
See under individual properties and also Plastics: Use plastics to investigate
other properties of materials.
Purity:
See Evaporation.
pure and impure liquids
Rates of reaction
Baking chemicals:
Use bicarbonate of soda with citric acid to compare rates of reaction.
Sugars and sweeteners:
Use artificial sweetener tablets to investigate rates of reactions.
Food additives: Use fizzy vitamin C tablets to demonstrate rates of reaction.
Recycling examples
Metals: Use metals as an important example of recycling.
Plastics: Use plastics as examples of materials that can be recycled.
21
Resistance, air and
Plastics:
water
Use polystyrene to make shapes to demonstrate air and water resistance.
Reversible and
Clay and modelling materials:
irreversible changes
Use pottery clay to demonstrate reversible and irreversible change.
Plaster of Paris: Use plaster of Paris to demonstrate permanent change.
See also section 3.4.
Rock identification and
hardness
Calcium carbonate: chalk and marble: Use calcium carbonate to demonstrate
identifying rocks and soils, and hardness.
Rocks and soils
In addition to activities under Soil see Clay and modelling materials:
Use clay as an example of everyday uses of products from rocks and soils.
Rusting
Metals: Use steel to demonstrate rusting as an example of chemical change.
Salad dressing
Acids: cola, lemon juice and vinegar:
Use lemon juice or vinegar to make salad dressing.
Scones
Baking chemicals: Making scones.
Slime
Glues: Use PVA glue to make slime.
Soil acidity
Acids: cola, lemon juice and vinegar: Testing soils for acidity.
Soil, types
Soil and gardening products: Use soil to explore speed of drainage.
Solutions
See Dissolving.
Solvents
See Dissolving.
Stomach acidity
Acids: cola, lemon juice and vinegar: Stomach acid.
Strength of materials
Cement and concrete:
Use cement to make concrete to compare the strength of different mixtures.
Surface tension
Soap and cleaning products:
Use detergent to break the surface tension on water.
Taste tests
See activities under Sugars and sweeteners and also
Food additives: Use food colouring in taste tests.
Tooth decay
Acids: cola, lemon juice and vinegar:
Use cola or fruit juice to demonstrate the effects of acid on teeth.
Calcium carbonate: chalk and marble:
Use calcium carbonate to demonstrate weathering or tooth decay.
Translucent material
Oils, waxes and chemicals derived from oil: Wax as a translucent material.
Variables, exploring
In addition to many examples see Rates of reaction and Oils, waxes and
chemicals derived from oil: Making candles and exploring variables.
Viscosity
Cooking oils and fats:
Use cooking oils as examples of liquids and demonstrating viscosity.
Food additives: Use glycerine to demonstrate a thick liquid.
Washing-up and
washing comparisons
Soap and cleaning products: Use safe detergents for washing-up and washing
comparisons.
Waterproofing
Oils, waxes and chemicals derived from oil: Use petroleum jelly for
waterproofing.
Wax, melting
Oils, waxes and chemicals derived from oil: Use wax to demonstrate the effect
of (moderate) heat on materials, a physical change.
Wax-resist
Oils, waxes and chemicals derived from oil: Wax-resist artwork.
Weathering
See Tooth decay.
22
Acids: cola, lemon juice and vinegar
Available from shops in bottles and cans.
What are they? These are all edible dilute acidic mixtures in
water. Strong acids can burn skin; these weak ones tend just to
make our tongues tingle. Acids also react with their chemical
opposites such as alkalis (see Bicarbonate of soda).
Cola is carbonated water containing citric acid and is flavoured
with vegetable extracts. Unless sold as decaffeinated, most cola
drinks also contain caffeine, which is a stimulant. Diet cola
contains artificial sweeteners; non-diet cokes also contain sugar.
Vinegar contains ethanoic
(acetic) acid and other
ingredients. Lemon juice and cola
contain citric acid.
How safe are
they?
A number of foods contain vinegar, eg, salad dresssings and
tomato ketchup. Other edible acids include sour milk, yoghurt
and cream of Tartar. A number of fruit juices contain citric acid.
Cola, lemon juice and vinegar are edible but they may irritate the skin or
eyes as they are weak acids. Avoid splashing on skin or in the eyes. They
should not be consumed in a science context. Vinegar normally contains
5 - 8% ethanoic acid and is low hazard (pure ethanoic acid is CORROSIVE).
Do not provide these in squeezy bottles or plastic ‘lemons’ if children are
likely to squirt them. Citric acid crystals are IRRITATING TO EYES but solutions
below 20% are low hazard.
Hazard label: None.
Suitability: Pupil use: normal supervision unless there is a high risk of splashing into eyes.
Use: Good ventilation when using vinegar. Take care with sensitive skins.
Disposal: Dilute and flush away.
Activities using acids
Use cola as a challenging example of floating and sinking
Unopened cola tins placed in water at least 30 cm deep will sink if
it’s ordinary cola and will float if it’s diet cola. The sugar in cola
gives it a greater density than water. Diet cola has a similar density
to water, so it floats. Put the cans in sideways; the dimple in the
base can hold air that could buoy up the can.
The picture shows cans of diet and non-diet colas in water.
If drinking later, only allow children to drink what they normally would. Maintain good hygiene.
23
Make and use an indicator: a substance that changes colours in acids and alkalis
Make your own indicators. Prepare a solution of coloured
fruits or vegetables. Many are good acid/base indicators:
they change colour depending on how acidic or alkaline
the solution they are in is. Red cabbage and beetroot
need to be boiled; berries might just be crushed. Soak
small pieces of paper towel to make indicator papers or
use drops of the solution. Test fruit juices, other drinks,
bicarbonate of soda and well-diluted washing products.
Red cabbage extract used to test acids
and alkalis. The papers are dry. The
colours look different while wet.
Avoid splashing the eyes. Take care with sensitive skins. Close supervision is needed for heating
activities and if using knives. If using commercial indicator preparations, read the label.
Use cola or fruit juice to demonstrate the effects of acid on teeth
You can put milk teeth into a container of one of these acidic drinks. Donated milk teeth should be
sterilised in a pressure cooker for 15 minutes and cooled before being handled (ask your local
secondary school if you don’t have a pressure cooker). After a day or so the teeth will become
noticeably soft. Luckily we do not immerse our own teeth for hours on end in these drinks but it’s
easy to see the harmful effects of frequent drinks and poor dental hygiene. In addition to the direct
effect of the acid, fruit juices and non-diet colas contain sugar which is converted to acid by plaque
bacteria in the mouth, exacerbating the problem.
See the section on Calcium carbonate for a similar activity using a piece of chalk instead of a tooth.
Use lemon juice or vinegar to make salad dressing
Add salt and sugar to the lemon juice or vinegar, allow them to
dissolve then mix with an equal quantity of cooking oil.
The mixture will separate out quite quickly. This will keep best in
a stoppered bottle. You can see through the sides that the olive
or vegetable oil is floating on top of the vinegar.
Avoid splashing the eyes. Take care with sensitive skins.
24
Make electricity from fruit
Fruit juices or even pieces can be
used to produce electricity, as
shown using the multimeter.
Use ‘copper’ coins and steel nails: galvanised nails contain zinc
and can provide a higher voltage. Clean the coins in lemon juice
or vinegar and rub the nails with sandpaper. Squeeze the fruit
slightly to rupture its cells and release juice, then insert these
‘electrodes’ in the fruit so they are close to each other but not
touching. Connect the circuit with one or more ‘cells’ (individual
fruits with one of each electrodes) in series so the electricity
generated flows around the circuit.
Four fruit cells may produce a high enough voltage but the current is probably too low to light a
small lamp, or even an LED (light-emitting diode), which takes quite a tiny current. Kits for making
various electrical devices are available from educational suppliers. Multimeters are sold in DIY
shops.
Take care with sharp edges. Do not eat the fruit.
Stomach acid
Indigestion tablets contain alkalis to neutralise excess stomach acid.
Remind children that the stomach contents are very acid and that they have tasted this if they have
ever been sick. Incidentally, explain that if they are unlucky enough to be sick, they should clean
their teeth to remove the stomach acids. See also Bicarbonate of soda.
Many foods including citrus fruits are quite acidic but are generally considered to be good for us
because they contain a mixture of many useful substances. See Food additives and supplements.
25
Alcohols and other solvents
Available in many different forms: surgical spirit can be suitable
for primary school science demonstrations.
What is alcohol? ‘Alcohol’ is a name for a family of similar
chemicals, though it commonly refers to ethanol or propan-2-ol
(sometimes called rubbing alcohol). Pure ethanol is a colourless
liquid that mixes with water and burns with a pale blue flame.
Surgical spirit contains mainly
industrial denatured alcohol.
‘Antibacterial’ hand products
often contain propan-2-ol.
Also known as: Ethanol: ethyl alcohol. Most applications use
impure forms, eg, Industrial denatured alcohol (IDA), previously
called Industrial methylated spirit (ethanol + 5% methanol);
mineralised methylated spirit (MMS; the purple, smelly liquid)
methylated spirits, meths. While widely used for DIY activities,
these are not generally suitable for primary school use. Propan2-ol: isopropanol.
Alcohol is contained in: Surgical spirit, tincture of iodine, duplicating fluid, after-shave lotion,
(‘antibacterial’) hand rubs and gels. Note that ‘spirit thermometers’ (sometimes named by colour:
‘red’, ‘blue’ or ‘green’) do not contain alcohol.
Be aware of some cultural objections to activities which use alcohol.
How safe is it?
Ethanol is a HIGHLY FLAMMABLE liquid and HARMFUL IF SWALLOWED.
Industrial denatured alcohol contains impurities to make it undrinkable.
Alcoholic drinks with water and flavourings are also not suitable for pupil use.
Surgical spirit or hand-rubs may contain propan-2-ol. When pure, this is
HIGHLY FLAMMABLE, IRRITATING TO THE SKIN and MAY CAUSE DROWSINESS
AND DIZZINESS. However, in commercial products, it is diluted and normally
low-hazard, so may be used on the skin: see the activity below.
Hazard label: Surgical spirit and hand-rubs containing alcohol are usually low hazard, though
more-concentrated formulations would be HIGHLY FLAMMABLE and possibly carry other hazards.
Suitability: Surgical spirit and hand-rubs: Pupil use: close supervision; Ethanol or propan-2-ol:
Teacher use only.
Storage: Store securely. Keep a log of quantities stored and used and check regularly.
Use: Good ventilation. Take care with sensitive skins.
Disposal: Small quantities may be allowed to evaporate in a well-ventilated area.
Propanone
Available from pharmacies and shops.
What is propanone? A colourless, HIGHLY FLAMMABLE liquid
with a strong and distinctive odour. Propanone is contained in
most nail varnish removers and can dissolve many substances
that are insoluble in water. It is also known as acetone.
Propanone is contained in: nail varnish and nail-varnish remover.
26
How safe is
propanone?
HIGHLY FLAMMABLE. Degreases skin. There is a risk of solvent abuse
(sniffing).
Hazard label: HIGHLY FLAMMABLE.
Suitability: Pupil use: close supervision.
Use: Use only small pieces, with good ventilation. There should be no flame, electric radiant fire, gas
wall heater or other naked flame in the room when propanone is being used. Avoid splashing on skin
or into the eyes. Take care with sensitive skins. Avoid use with children who may drink the liquid or
try to inhale the vapour. Pupil use: close supervision.
Disposal: Allow the solvent to evaporate in a secure, well-ventilated place.
Storage: Secure. Only very small quantities of nail-varnish remover should be kept.
Activities using alcohol
a) Use surgical spirit or hand-rubs to demonstrate evaporation
Ethanol has a lower boiling point than water (78 °C) so evaporates
more quickly at room temperature. The process of evaporation
takes heat from the body. So, for example, after-shave lotion feels
cold. Evaporating water does so too but the effect is more apparent
with alcohol.
b) Use surgical spirit to demonstrate dissolving, as an alternative solvent to water
Water is not the only solvent; alcohol dissolves candle wax and
margarine, which could be shown as a teacher demonstration.
Alcohol is used as an industrial solvent for gums, resins, lacquers
and varnishes; for essential oils in perfumes; and for medical
substances in pharmacy (see also activity using propanone on the
next page).
The picture shows surgical spirit being used to dissolve and wipe
away writing from a ‘permanent’ (non water-soluble) marker.
HIGHLY FLAMMABLE. Teacher use only. Take care with sensitive skins.
Ethanol is produced during bread making by yeast
Fermentation of yeast produces alcohol and carbon dioxide. The
alcohol then evaporates away when heated during baking. See the
bread recipe over the page and suggestions for investigations
under Baking chemicals.
The picture shows yeast which has been fermenting in sugary
warm water for a few minutes.
Usual hygiene precautions for preparation of food. Pupil use: close supervision.
27
Making bread or bread rolls.
Wash your hands and clean surfaces before you begin. See section 2.7 for guidance on hygiene.
Ingredients
200 g plain strong flour
15 g fresh yeast*
25 ml warm vegetable oil
100 ml warm water
1 level teaspoon salt
Milk or water for glazing
1 teaspoon sugar
Method
•
Put the flour and salt through a sieve into a warm (35 - 40 °C) mixing bowl.
•
Mix the warmed (35 - 40 °C) oil with the flour using a wooden spoon.
•
Cream the yeast and sugar with two teaspoons of warm water (35 - 40 °C) in another bowl and
then add the remainder of the water to the creamed yeast.
•
Stir the yeast mixture into the flour mixture to make the dough.
•
Put the dough on to a floured board or tabletop covered by a clean plastic sheet. Knead the
dough (involves stretching it also) until it is really smooth.
•
Cover the dough with ‘Clingfilm’ (wiped with oil to prevent sticking to the dough) and leave to
rise in a warm place (35 - 40 °C) until it has doubled in size (about 20 minutes). Remove the
Clingfilm and knead the dough again for a further 5 minutes.
•
Shape the dough into a loaf or divide the dough to make rolls. Put the loaf into a bread tin or put
the rolls on to a baking sheet.
•
Cover the bread or rolls again and leave to rise until double their original size.
•
Remove the Clingfilm and glaze the tops with milk or water.
•
Bake in a hot oven at 425 °F (220 °C or gas Mark 6 - 7) for 10 minutes (special care is
required). Reduce the temperature to 35 °F (180 °C or gas Mark 4 for a further 30 - 45 minutes
for loaves, 5 - 10 minutes for rolls. NB Rolls may need to be on a lower shelf to prevent burning.
•
Test loaves or rolls by tapping lightly on the under side. They should sound hollow when ready.
Remove bread from the baking tin and leave to cool.
* Fresh yeast can be obtained from bakers and will keep refrigerated for up to 4 days. Alternatively,
dried yeast can be mixed with the sugar and a small quantity of warm water about half an hour
before preparing the dough.
Activity using propanone
Use nail-varnish remover to demonstrate dissolving as an alternative solvent to water
Nail-varnish remover is sometimes suggested as an alternative solvent to water. Clearly it dissolves
nail varnish, which is waterproof. It should only be used in small quantities, under close supervision
and away from naked flames. There is a risk of solvent abuse. Other alternative solvents include
surgical spirit: Some plastics may dissolve in nail-varnish remover.
There should be no flame, electric radiant fire, gas wall heater or other naked flame in the room
when propanone is being used. Avoid splashing on skin or into the eyes. Take care with sensitive
skins. Avoid use with children who may drink the liquid or try to inhale the vapour.
28
Baking chemicals
(a) Bicarbonate of soda
Available from pharmacies and shops.
What is bicarbonate of soda? A white crystalline solid,
bicarbonate of soda is a weak alkali. Do not confuse this with
washing soda (see Cleaning products). Bicarbonate of soda is a
component of baking powder, which also contains cream of tartar
and often wheat products.
Also known as: Sodium bicarbonate, sodium hydrogencarbonate.
Bicarbonate of soda is contained in: baking powders, self-raising flour, sherbet and bath salts
(these may also contain sodium carbonate, which is IRRITATING TO EYES).
How safe is it?
Bicarbonate of soda is a weak alkali. It can irritate the eyes and reacts with
acids to produce carbon dioxide gas. Take care to avoid splashing or rubbing in
the eye. Allow for the (sometimes surprising) volume of gas produced if it reacts
with an acid. Ensure good ventilation when reacting it with acids, to enable
carbon dioxide to diffuse away and be replaced by fresh air.
Hazard label: None.
Suitability: Pupil use: supervision depends on the activity.
Use: Avoid rubbing or splashing into eyes. Good ventilation for reactions with acids. Take care with
sensitive skins.
Disposal: Dissolve in water, dilute and flush away.
(b) Flour
Available from grocers and supermarkets.
What is flour? Generally, ground plant material containing a
high proportion of starches (carbohydrates consisting of long
chains of sugar molecules). Flour may contain some protein
and fat. Starches can be made from grains (eg, wheat, barley,
oats or rye), pulses (eg, gram) or other vegetables or fruits (eg,
corn, banana). Cornflour is a very fine-grained flour made from
maize. Instant mashed potato is another high-starch product.
Flour is contained in: baked goods (breads, cakes, biscuits), puddings, eg, custard powder, instant
whips) and as a thickener or glazing agent in many other food products. Self-raising flour contains
raising agents, similar to baking powder.
How safe are
they?
Low hazard in small-scale use. The fine dust may be a nuisance and some
children may be allergic to certain types, possibly only on ingestion.
Take care to prevent clouds of dust from dry flour. There is a risk of inhalation
and flour can give rise to short term respiratory, nasal and eye symptoms. It
may provoke an asthmatic attack in individuals with pre-existing disease.
29
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Avoid raising dusts. Check for allergies.
Disposal: Wrap and place in normal refuse.
Activities using bicarbonate of soda
Use bicarbonate of soda to demonstrate pH
pH is a measure of how acidic or alkaline a solution is. You can
buy indicators such as litmus or universal indicator as packs of
impregnated paper strips, or you can prepare your own indicator
before the lesson. See Acids for details.
The picture shows books of red and blue litmus paper and that
bicarbonate of soda solution makes red litmus turn blue.
Warn children to avoid splashes or rubbing the solution into their eyes.
Use bicarbonate of soda with citric acid to compare rates of reaction
The mixture in the right-hand
beaker has been stirred and has
finished reacting. The mixture in
the left-hand beaker, which has
not been stirred, is still reacting.
These chemicals react together, producing carbon dioxide (which
makes the mixture fizz) and sodium citrate which dissolves in the
water. Because citric acid crystals are IRRITANT, the teacher or a
TA should prepare a citric acid solution, which is low hazard, by
dissolving about 5 g (1 teaspoon) citric acid crystals in 500 cm3
water. Pupils can then add about 2.5 g (½ teaspoon) of
bicarbonate of soda to about 100 cm3 citric acid solution in a
500 cm3 container and compare the rate at which the mixture
reacts when stirred / left alone and in warm / cold water.
Pupils can, with supervision, add the bicarbonate of soda to citric acid solution. The mixture will fizz
while the chemicals react together. Use a large enough beaker to contain most splashes. Water for
heating should not be above 50 °C. Warn pupils to be careful about splashes and not to rub their
eyes. Wash hands after the activity.
Use bicarbonate of soda to inflate balloons and kitchen gloves with carbon dioxide gas
Make ‘King Kong’s hand’ using a washing-up glove secured over
the neck of a bottle. Put bicarbonate of soda in the fingertips and
vinegar in the bottle. Once the glove is secure, tip the bicarbonate
into the vinegar. Carbon dioxide gas is produced which inflates
the hand.
Teacher use only. Good ventilation. Avoid splashes to the eyes.
30
Use bicarbonate of soda to demonstrate carbon dioxide gas as a fire extinguisher
The mixture froths as carbon
dioxide is produced when vinegar
is added to the bicarbonate of
soda in the jar.
A floating candle is extinguished by carbon dioxide gas. Float a
tea light in a jam jar containing a small amount of water and a
generous amount of bicarbonate of soda. Light the candle with a
long splint: it may help to tip the jar slightly to allow the candle to
float near to the mouth of the jar. Carefully, without dousing the
candle, pour vinegar to the water / bicarbonate mix. The floating
candle is extinguished by carbon dioxide gas, which displaces any
oxygen from air in the jar. You will need to practise this
beforehand to work out how much water, bicarbonate of soda and
vinegar to use.
Teacher demonstration only. Good ventilation. Avoid splashes to the eyes. Care with flames.
Use bicarbonate of soda to make bath bombs
Mix bicarbonate of soda, citric acid and cooking oil with a little
food colouring. Allow the mixture to harden, then add to water for
an ‘explosive’ effect.
Allow plenty of space: use a fairly large container like a sand or
water tray.
Pupil use: close supervision. Warn not to rub eyes and avoid splashes to the eyes. Gloves may help
for those with sensitive skins. Pupils should be far enough away to avoid being splashed when the
‘bomb’ is added to water. The water will become oily and may be slightly acidic or alkaline but can be
drained as usual and washed up with washing-up liquid. It is not advisable to allow pupils to take
these home. You can’t know what will happen to it once it leaves school; younger siblings may eat it
and it can make an unexpected mess.
Use bicarbonate of soda to neutralise the smell of sick.
Because vomit is acidic, once cleared up and disinfected, its smell can be neutralised by washing
splashed surfaces with dilute bicarbonate of soda, which is an alkali.
NOTE: do not use with proprietary packs for clearing up body fluids, which may contain incompatible
substances.
31
Activities using flour
Use flour for bread baking and cooking activities: edible examples of chemical change
Vary the bread by using different types of flour. Make unleavened
(yeast-free, unrisen) breads or Matzot and leavened (risen) bread
and compare the two. Yeast-free risen bread, eg, soda bread can
be made using self-raising flour or plain flour with baking powder.
See under Alcohol for a bread recipe and below for a scone recipe.
Avoid raising dusts. Check for allergies. Take usual care for hygiene and hot items.
Making scones.
Wash your hands and clean surfaces before you begin. (See section 2.7 for guidance on hygiene.)
Ingredients
225 g self-raising flour*
50 g margarine or butter
1 pinch of salt
150 ml milk or water
½ a level, 5 ml spoonful bicarbonate of soda
Method
Heat the oven to 240 °C or gas Mk 8.
Sieve together flour, salt and raising agents (if used). Rub in the fat using fingertips only. Make a well
and pour in most of the milk or water. Stir the fluid so that the flour is gradually mixed in, to make a
light dough, just firm enough to pick up (add more fluid if needed). Turn the dough onto a floured
board and press or roll it until it is 1.5 to 2 cm thick. Cut into shapes and place on a floured baking
tray. Bake near the top of the oven for 8 - 10 minutes until brown.
* You can also use plain flour with 2 level, 5 ml spoonfuls of baking powder, or plain flour with 1 level
5 ml spoonful of Cream of Tartar and ½ a level, 5 ml spoonful bicarbonate of soda.
Use flour as an example of an insoluble solid
Well-mixed, flour and water can make a paste but the flour doesn’t dissolve to make a clear solution.
Over time the suspended particles might settle.
32
Use cornflour to make a non-Newtonian material
Prepare by adding water to a little fine white cornflour (not the other
way round) stirring slowly with a metal spoon. Do not use coarsergrained polenta. The mixture soon begins to thicken. When it is thick
enough you can scoop some out and hold it in your hand. You can
squeeze it into a ball and it will hold the shape for a moment; then it
collapses into liquid, running through your fingers. This behaviour
contrasts with the properties of typical Newtonian liquids (most
everyday examples such as mud). These flow more quickly if more
force is applied to them, eg, they are squeezed.
Add a bit of food colour to this strange mixture and you have what American teachers call ‘Ooblek', a
‘strange material from an unknown planet’.
The paint that comes in solid blocks in a tray is a non-Newtonian material. In the tray it is solid - on
the brush it is a liquid. If you have ever wriggled your feet in the sand on holiday and found the wet
sand turning to jelly under your feet, you have experienced the same sort of thing.
Avoid raising dusts. Check for allergies.
33
Balloon gas (helium)
Helium is contained in: helium balloons.
Available from party suppliers, either for hire in
cylinders or for sale in non-reusable canisters.
What is helium? A colourless, odourless, inert gas
that is less dense than air.
Special balloons with metallic coatings are usually
filled with helium, although ordinary rubber balloons
may be used.
Gas can seep out around the fastening or through tiny pores in the wall of a rubber balloon, causing
the balloon to deflate gradually. Helium particles are smaller than most of the particles in air, so a
rubber balloon filled with helium will deflate more quickly than one filled with air.
Also known as: Balloon gas.
How safe is
it?
Do not inhale helium. It can be fatal if inhaled from a pressurised container and can
be dangerous even from balloons. It is also not good practice to show children
unsafe activities that they may be tempted to copy.
Hazard label: None.
Suitability: Teacher use only.
Use: Store securely. Large cylinders should be transported on a trolley. Ensure that canisters are
stable and follow all instructions carefully.
Disposal: Cylinders should be returned to the hiring company. Empty canisters may be accepted at
your local recycling centre.
Activities using helium
Use helium for balloon races in work on gases
Using toy balloons and lightweight, waterproof labels, it is possible to run a balloon race. Balloons
must be filled by a teacher and should be released when the wind favours good dispersal, avoiding
the risk of drifting at low altitude across a road or rail track. Always use the school address, not
private addresses. Record finds on a large-scale map to chart their travels.
Teacher use only. Keep children at a distance and only fill and release one balloon at a time. Warn
watching children against looking directly at the Sun. This is not a suitable activity in the vicinity of
airfields or other locations where balloons may be a nuisance.
34
Calcium carbonate: chalk and marble
Available from the ground in some places and from
shops and educational suppliers.
What is calcium carbonate? A mineral made of
carbon and oxygen combined with calcium.
Also known as: calcite.
Lumps of chalk.
Calcium carbonate is contained in: limestone, marble, chalk; some blackboard chalks. The White
Cliffs of Dover and other chalk cliffs contain calcium carbonate.
How safe is it?
This chemical, whether used in lumps (marble, limestone or chalk) or
powdered chalk, is low hazard except that the fine dust may be a nuisance.
Heating a lump of limestone to produce quicklime, as suggested in some
texts to demonstrate making concrete, is not a suitable activity in a primary
school. A substantial heat source is required and the quicklime produced is
particularly hazardous to the eyes.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Avoid raising dusts. Take care with sensitive skins.
Disposal: Wrap and place in normal refuse.
Activities using calcium carbonate
Use calcium carbonate to demonstrate identifying rocks and soils, and hardness
Calcium carbonate scratches with a bronze coin but not with a
fingernail. Hardness 3 on Moh’s scale. It fizzes with mild acids
like vinegar. To identify it, add a small piece to some dilute acid.
If fizzing occurs (due to the production of carbon dioxide) then
the sample contains calcium carbonate.
Avoid splashing the eyes. Take care with sensitive skins.
35
Use calcium carbonate to demonstrate weathering or tooth decay
Place a small lump in a beaker of cola drink, lemon juice or
vinegar and observe changes over time (see the picture). If
using blackboard chalk, test it beforehand; some products don’t
contain calcium carbonate. This demonstration can also be done
with teeth, although these contain a different calcium compound
(see Acids for details).
The picture shows a piece of chalk in lemon juice.
Avoid splashing the eyes. Take care with sensitive skins.
Rain tends to be slightly acidic due to dissolved carbon dioxide from the air. It can react with calcium
carbonate in rocks, producing a solution of calcium hydrogencarbonate (which, incidentally, has
some similar properties to bicarbonate of soda). This reaction is reversible and when the solution
evaporates, calcium carbonate is deposited. This is how stalactites are formed on the roofs of
limestone caves; solutions dripping from the tips of stalactites onto the floor of the cave may similarly
form stalagmites.
Demonstrate double refraction in calcite
A lump of calcite will refract light to form two images. Suitable
samples are available from some educational suppliers or
museums / science activity centres.
The picture shows a piece of calcite standing on a printed page.
36
Cement and concrete
Available from DIY shops and builders’ merchants.
What is Portland cement? A powder made by burning a
mixture that includes calcium carbonate and clay. When mixed
appropriately with water and sand or gravel, cement is made into
mortar or concrete.
Concrete is a practical and durable building material.
Portland cement is contained in: concrete, mortar and grouts.
How safe is
it?
The grey powder is so fine that it can be easily blown into the eyes where it can
cause injury as it is strongly alkaline. The powder is an IRRITANT in contact with
eyes, respiratory system and skin. Safety spectacles should be worn while handling
it. Avoid contact with the skin. Ensure a supply of water is close by in case irrigation
is needed.
Pupils can use wet cement but disposable gloves should be worn; eye protection
should also be worn and running water should be available in case irrigation is
needed. Immediately irrigate spills on skin or splashes in the eyes.
Hazard label: Dry powder: IRRITATING TO RESPIRATORY SYSTEM AND SKIN; RISK OF SERIOUS
DAMAGE TO EYES. Wet mixture: IRRITATANT; RISK OF SERIOUS DAMAGE TO EYES.
Suitability: Teacher use only; Mixed cement: Pupil use: normal supervision.
Use: Wear protective gloves and eye protection when handling the dry powder or wet materials.
Avoid contact with the skin.
Disposal: Allow to harden and place in the normal refuse.
Activities using concrete
Use cement to make concrete to compare the strength of different mixtures
Using plastic packaging or cardboard moulds, it is possible to pour and set a range of lintels of
different sizes and shapes. Set these as bridges and test them with weights hung from the centre.
Burying wire in the setting cement simulates reinforced concrete.
Concrete can be made by taking three or four parts of sand and gravel and one part cement, mixing
it to a slurry with water and leaving it to set and dry out in a plastic mould.
Pupil use: close supervision. Secure the lintels well. Place a box of crumpled newspaper in a tray
under the lintel test so that the weights will fall in there, rather than on feet.
37
Clay and modelling materials
Available from educational suppliers and craft shops.
What is clay? Clay is a fine-grained rock. The largest particles are
invisible to the naked eye. When baked (‘fired’), it changes chemically
(fired products are called ceramics). Modelling materials with different
properties are available.
Air-drying clay contains glass fibres that help bind it together. There are
two alternative forms of hardener: one is added to the clay before use and
the other is painted on the finished product.
The pots in the picture are made from clay. The paler one has not been treated and may have only
been fired once. The darker one was made from darker clay. After the first (‘biscuit’) firing, colouring
agents, including some glazes (colours mixed with a substance that becomes glassy when heated)
were applied before it was fired again at a very high temperature. Bricks and roof tiles are also made
from fired clay.
How safe is it?
Small quantities should not pose significant hazards. Avoid raising dusts. Gloves
may be sensible with sensitive skins.
‘Kiln firing’ is a teacher-only activity.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Avoid raising dusts. Take care with sensitive skins.
Disposal: Wrap and place in normal refuse. Clear up spills using a damp cloth or mop to avoid
raising dusts.
Activities using clay
Use pottery clay to demonstrate reversible and irreversible change
Clay is used in a wide range of art and craft activities including
making pottery, modelling and slipware. Investigate the effects of
drying and heating. Clay is changed by gentle heating or drying
into a hard but non-waterproof material and by baking, which
chemically changes it to pottery. Drying can be reversed; baking
cannot. Glazed pottery is usually waterproof.
Take care with sensitive skins.
Use clay as an example of everyday uses of products from rocks and soils
Ask children to count the ‘rocks and soils’ in their bathroom.
Ceramic sinks, toilets and possibly baths, tiles and mirrors all
started out as rocks or soils. You might add talc and pumice.
38
Cooking oils and fats
Available from shops.
What are cooking oils? Greasy, non water-soluble liquids from
vegetable and / or animal sources, eg, soya bean, sunflower seed,
peanut, cottonseed, palm kernel, olive or beef, pork or chicken.
‘Pure’ oils probably come from a single source but technically they
are all mixtures of chemicals that differ slightly. Nutritionally, oils are
classed as fats.
Other oils: Oils from vegetable sources are generally liquids at room temperature (palm kernel and
coconut oils are exceptions). Solid oils, usually called fats, include butter and lard. Note that
beeswax is actually mainly a mixture of heavy oils!
Cooking oil is contained in: a number of foods including dressings.
Be aware of religious and vegetarian / vegan restrictions, if using fats or oils in cooking.
How safe is it?
Some oils may contain allergens. Spilled oils can be slippery. Cooking oils
are, as their name suggests, generally safer than petroleum-based oils but
see Oils, waxes and chemicals derived from oil for safety information on the
disposal of linseed oil.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Do not use oils that may contain an allergen (particularly peanut) in a room with an allergic
individual. Clear up spills promptly and thoroughly.
Disposal: Small quantities may be absorbed onto paper towels, wrapped and placed in the normal
refuse, or add plenty of detergent and flush the mixture away.
Storage: Keep in a cool, dark place and dispose of samples if they do not smell fresh.
Activities using cooking oil
Use cooking oils to demonstrate fats in foods
Oil is a fat that is liquid at room temperature. A drop of oil forms a
translucent ‘window’ on paper. This ‘grease-spot test’ can be used
to show demonstrate which foods contain fats. Rub the food on
absorbent paper, dry and view against fairly strong light.
The picture shows a drop of oil on some filter paper. Even when
dry, the spot will look translucent.
Check for allergens. Clear up spills promptly. Do not eat unless strict hygiene is followed.
39
Use cooking oils as examples of liquids and for demonstrating viscosity
Oils are more viscous than water: they flow more slowly. Objects
released simultaneously into different liquids, eg, water, syrup and
cooking oil, fall at different rates. Try this in a tall container like a
clear plastic measuring cylinder. Attach a thread to the object to
recover it without mess.
The picture shows similar shapes made from modelling-clay
falling through water and cooking oil.
Check for allergens. Clear up spills promptly.
Use cooking oil to demonstrate that oil floats on water and the effect of emulsifiers
Cooking oil floats on vinegar because it is less dense. For any
volume of liquid, the vinegar will weigh more than the same
amount of oil, as you can show by measuring the weight of
samples of the same volume. This can come as a shock. Oil,
after all, is thicker than vinegar and you might expect it to be
denser. Mix the two and the oil will float, as it does on water.
You can see through the sides of the bottle that the olive or
vegetable oil is floating on top of the vinegar.
The pictures show oil and water: washing-up liquid has been shaken with the contents of the right-hand
bottle. The washing-up liquid helps the oil and water to mix and stay together, at least for a while!
Set the children a challenge. You are having a salad for lunch. You would really like just oil from the
bottle - or just vinegar. Oil is easy enough. Tilt the bottle slightly and it will run out. But the vinegar
is a problem. The trick is to put the stopper in, invert the bottle, and then pull the cork just a little,
letting out a jet of vinegar.
Mayonnaise is an emulsion of oil and vinegar. Adding egg yolk (an emulsifier) to the ingredients
enables them to mix.
Check for allergens. Clear up spills promptly.
Use beeswax to reduce friction by lubrication
Oils can lubricate a surface. Oiling dough prevents it sticking to its container while it rises. Beeswax
or mineral oils are suitable for lubricating mechanical parts in models. Demonstrate using a spring
balance to pull waxed and unwaxed blocks along the floor.
Check for allergens. Clear up spills promptly.
40
Food additives
Available from grocers and supermarkets.
What are food additives? We include here a diverse range of
edible substances used in food production. Gelatine is a
colourless, tasteless, transparent, water-soluble protein derived
from animal products containing collagen (eg, bone or horn). It is
used to thicken or ‘set’ liquid foods.
Glycerine is a thick, colourless, odourless, sweetish liquid derived from vegetable or animal oils
and fats. Small quantities of vitamin C are essential to health; it is an antioxidant and it is added to
foods to protect them from deteriorating quickly. Spices are usually plant-derived, though packaged
spices may include other ingredients.
Glycerine is also known as: glycerol or propane-1,2,3-triol.
Vitamin C is also known as: ascorbic acid.
Gelatine is contained in: jellies and many sweets and baked goods. Glycerol is an additive in
many food products, as are food colours. Vitamin C is added to many food products as an
antioxidant.
How safe are
they?
Generally safe, but note that gelatine and glycerol, some jelly cubes and food
colourings may be made with animal products, possibly from pork, making
then unsuitable for use by some religious and ethnic groups. Check the
ingredients. Stains from concentrated food colouring are hard to remove;
avoid staining clothes, skin and surfaces. Some children may be sensitive to
certain food colours. Vitamin C is a mild laxative in large quantities. Do not
use tablets with children that may ingest them.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Check for sensitivities, including religious and cultural issues.
Disposal: Flush liquids away; wrap solids and place in the normal refuse.
Activities using food additives
Use food colouring in taste tests
Use food colour to dye bland foods (milk, instant whip, instant mashed potato) and compare real
and imagined flavours. Who will eat blue mashed potato?
Avoid staining clothes, skin and surfaces. Observe scrupulous hygiene precautions and explain
these to the pupils. Take care over diabetics and children suffering from obesity or sensitivities.
Dispense only the quantities needed. Wash hands and clean surfaces well, before and afterwards.
41
Use gelatine to demonstrate melting and dissolving
Jelly cubes are a gel: a liquid in a solid lattice. They melt when
heated and both melt and dissolve in warm water (drop a cube
into a glass of warm water: see the picture). Jelly cubes offer
manageable variables when dissolving, including water
temperature, size of jelly pieces, stirring and, of course, colour.
Scrupulous hygiene is needed if products are to be eaten. Check for sensitivities, including religious
and cultural issues.
Use glycerine to make strong, longer-lasting bubbles
A few drops of glycerine added to bubble mixture results in bigger,
longer-lasting bubbles. Mix together 10 parts liquid detergent
(washing-up liquid), 85 parts water and 5 parts glycerine.
Avoid splashing the eyes. Take care with skins that might be sensitive to the detergent.
Use glycerine to demonstrate a thick liquid
The slope is set up with a plate to catch drips.
Glycerine, honey, syrup and some food oils are very thick (viscous) liquids. Pour a small quantity
from a spoon or plastic pipette onto a sloping surface and watch it travel downwards. They flow but
relatively slowly. Discuss why they are still considered liquids.
The right hand picture shows small amounts of glycerol (on the left) and water flowing down a
sloping surface. Try comparing the speed of warm and cool samples.
Avoid splashing the eyes. Take care with sensitive skins. Clear up spills immediately.
42
Use food colouring to make water easier to see, eg, comparing cold and hot water
Fill two 2-litre pop bottles with tap water, one hot and
one cold. Leave them to settle. Using a plastic
dropper, add a few drops of food colour to each. Ask
children to observe and record the differences as the
colour swirls and spreads. A sheet of white paper
behind the bottles makes the effect clearer.
The dye in the food colouring dissolves in the water then diffuses until all the water in its bottle is
evenly coloured. In addition, convection currents (movements of water of different temperatures) in
the warm water help the red colouring to rise through the water and spread more quickly.
Long straws were used to insert the
colours near the bottom of these cups. The
warm water rises, carrying the red colour
round more quickly. Alternatively, soak
water-retention granules (used in plant
pots) in food colouring, dry and drop into
water to observe the water currents.
Avoid staining clothes, skin and surfaces. Cap the bottles if leaving them for children to view over
time.
Use foods containing vitamin C as examples of healthy eating
Small quantities of vitamin C are essential to health. Unlike most mammals, humans can’t make
vitamin C. We get it from fresh fruit and vegetables. Carnivores don’t have fruit and vegetables as a
vitamin C source and animals like tigers make their own.
Check children’s food sensitivities. Do not allow children to eat vitamin tablets.
Use fizzy vitamin C tablets to demonstrate rates of reaction
Effervescent tablets contain sodium hydrogencarbonate and citric acid; this is why they ‘fizz’ as
they are mixed with water. Pupils can compare the rate tablets react in cold or warm water or how
quickly whole and broken tablets react.
Dispense only the number needed. Use alternatives with children who might be tempted to ingest
the tablets. Use brown sugar or see Bicarbonate of soda for an alternative rates of reaction activity.
43
Glues
Available from craft and hobby shops, educational suppliers
and DIY outlets.
A synthetic resin and two
water-based glues.
How safe
are they?
What are glues? Materials that hold things together by
surface action, though strictly the word applies to those
derived from animal or plant sources. Solvent-based glues
may be dissolved in water (eg, simple paper glues, wallpaper
pastes and PVA glues) or an organic solvent (these usually
have characteristic smells and include, eg, polystyrene
cement). Synthetic resins often come in two parts: a resin and
a hardener; these have to be mixed to set the glue;
‘superglues’ only need moisture to set the resin. Glue guns
melt the glue, which then sets as it cools.
Always use a lower-hazard glue if a suitable one can be found. For more information
on glues, see Guide L18 Glues and adhesives.
Solvent-based glues: Do not allow near naked flames, electric radiant fire, wall gas
heater etc. Use small quantities and ensure good ventilation. Store solvent-based and
superglues in a locked cupboard. Risk of solvent abuse.
Superglues: IRRITANT.
Balsa cement: HIGHLY FLAMMABLE; risk of solvent abuse.
Low-temperature glue-gun glue: Employers may have safety guidelines on the use
of glue-guns and these MUST be followed. Pupils should not use high-temperature
glue guns. Some manufacturers supply low-temperature melt glue in sticks with an
oval cross section. They cannot be used in hot-melt guns designed for use with sticks
with a circular cross section. Long glue sticks are unwieldy so cut them into
manageable lengths.
If hot glue touches skin, irrigate immediately with cold tap water. (If a sink is not
available, have a bucket or large bowl of water readily accessible but not near enough
so that a gun could fall into the water). Keep the burn under cold water for at least
10 minutes (longer if it still feels hot). If necessary, seek first-aid.
Wallpaper paste: Cellulose and starch based pastes without fungicide are preferable
and can be obtained from school suppliers. These are LOW HAZARD.
Hazard label: Solvent-based glues and balsa cement may be HIGHLY FLAMMABLE or EXTREMELY
FLAMMABLE and IRRITANT.
Suitability:
Superglues: Teacher use only.
Glue guns: Pupil use: close supervision. Use low-temperature glue guns.
Wallpaper paste: pupil use: normal supervision.
Other glues: Pupil use: close supervision. Substitute water-based wood glues whenever possible.
Use: Check the label for hazards and guidance on the use of a product. Do not allow naked flames
or gas or radiant heaters in the room during use. There is a risk of solvent abuse. Wallpaper pastes
may contain fungicides. Wash hands after use. For all glues, take care with sensitive skins.
Disposal: Allow to harden, wrap and place in the normal refuse.
44
Activities using glues
Use glue for general model making
Use water-based glues unless waterproofing is needed, eg, for model boats where water-resistant
PVA can be used. Solvent-based glues may be needed occasionally.
Take care with sensitive skins and check the hazards of the product.
Use low-temperature glue-gun glue for modelling and making joints and to mount electrical
components
Glue guns can be used to mount small, electrical components, eg, bulb holders or motors.
Have cold water available in case of burns. Remind pupils that the glue and the guns become hot.
Use wallpaper paste to make papier mache for modelling
Avoid pastes containing fungicides. Make sure pupils wash their hands after handling wallpaper
paste.
Use PVA glue to make slime
Dilute about 25 cm3 of PVA glue to about 100 cm3 in water and mix well (some types may already
be diluted). Dissolve 1.0 g of borax in 20 cm3 warm water. Mix the solutions and stir vigorously. The
proportions can be varied to produce different qualities of slime and food colours can be added for
effect. See how quickly it slithers down a block!
Borax (sodium tetraborate) is classified as TOXIC with Risk phrase R63 Possible risk of harm to the
unborn child. This appears worrying but at the dilutions used (which are under 8.5%) borax is not
classified as hazardous and this activity has been carried out in schools for many years with no
problems. The main risk arises when making up the solutions. The teacher should wear eye
protection and take care to avoid spills or raising dust. Exposure is then minimal. Make the slime in
a cup lined with cling film and wrap it, or use disposable gloves when handling it. Do not allow
children to take the slime out of the classroom. Dispose of it by wrapping it and placing it in the
normal refuse within a couple of days.
45
Metals
Available from educational suppliers as blocks and sheet. Iron is
also available as filings. Aluminium is available as cooking foil
from shops.
What are metals? Materials that are good conductors of heat
and electricity; they usually reflect light well, are malleable and
are often cold to the touch.
Samples of metals from a
scientific supplier.
How safe are
they?
Metals are contained in: coins, jewellery, vehicles, many items
of furniture, building parts and toys. Aluminium foil is also known
as cooking foil and erroneously as ‘tinfoil’. Note that pencil ‘lead’
is actually graphite (a form of carbon) or a mixture of ceramic
materials, and is therefore not a metal.
Aluminium, brass, iron, copper and zinc blocks, rods and sheets are low
hazard. So is lead - but hands should be washed after use. Avoid use with
children who may put it into their mouths. Beware of sharp edges and
corners.
Iron filings: close supervision is needed. Children may pick these up on
fingers and then rub their eyes causing irritation. Whenever possible, filings
should be kept in closed containers, eg, in sealed, plastic, transparent
wallets.
Nickel and nickel-plated metals: nickel can sensitise susceptible
individuals.
Lead: TOXIC.
Mercury: Mercury is TOXIC. Spilled residues remain for long periods. Though
not life-threatening, it is not eliminated from the body and can accumulate,
leading to long-term effects. Mercury-filled thermometers (the liquid inside
looks silvery) are not suitable for primary school use. Offer any that you find
to a local secondary school. Mercury spills need thorough treatment. Consult
CLEAPSS or a local, secondary science department.
Hazard label: None.
Suitability: Pupil use: blocks and aluminium foil: normal supervision; iron filings: close supervision.
Use: Take care with sharp edges and corners.
Iron filings: Avoid rubbing into eyes. Have eye wash facilities available. Pupils should only use iron
filings in sealed containers.
Nickel and nickel-plated metals: check for allergies; sensitive individuals should avoid contact.
Disposal: Wrap and place in the normal refuse if they can’t be recycled.
46
Activities using metals
Use metals to demonstrate electrical and thermal conductivity
Blocks or rods of metals are useful for these activities.
The picture shows that a metal spoon conducts electricity. The
wires are coated with coloured plastic (the colours are not
significant) and connect the battery, bulb-holder and spoon.
For comparison, use a plastic spoon instead. Break the circuit
by unclipping one connection: this is a simple switch.
Smooth sharp edges. For electrical conductivity, avoid the risk of short circuits: use cheap
disposable batteries, store them carefully and do not allow the poles to be connected with just one
wire or piece of conducting material. For thermal conductivity, see section 2.4 Safety when heating
and cooling.
Use metals to demonstrate that they react with acids
Tomato sauce on a coin.
This aluminium foil was left in a dish of citric acid
solution for a couple of days.
A new coin gradually discolours. Metal at the surface of the coin reacts with gases in air to make
new substances that look less shiny than the metal. Mildly acidic foods like tomato ketchup will
clean tarnished ‘copper’ coins and ‘eat’ into aluminium foil. The acid can react with some of the
impurities and remove them from the surface of a tarnished coin and can also react with the
aluminium foil. Fortunately, jewellery metals (gold and silver) are unreactive. However, it is wise to
avoid prolonged contact with acids, in case the jewellery contains other metals that do react.
Smooth sharp edges. Avoid splashes to the eyes. Wash hands after the activity.
47
Use metal blocks and objects to demonstrate magnetism
Only iron and steel - and a few rarer metals – are magnetic.
The composition of ‘copper’ coins has changed in recent years;
some are now magnetic.
The picture shows objects containing iron or steel being
attracted to a magnet. Some objects have become magnetised
by induction and so are able to attract others to themselves.
The coin is made from copper-plated steel; compare its
behaviour to pure copper, eg, an off-cut of copper piping.
Smooth sharp edges. Avoid the risk of dropping or knocking against parts of the body.
Use iron filings to demonstrate magnetic fields
Iron filings indicating the magnetic
field pattern of a bar magnet which
is under the card.
To demonstrate the magnetic field around a magnet and the
important part played by the poles, sprinkle iron filings on
paper placed over the magnet. Tap the paper lightly to help the
pattern form, and sandwich it with damp tissue; left for a week,
the filings will make a permanent rust pattern on the paper.
Keep magnets in a clear plastic bag, box or wallet to avoid
filings sticking to them in an unwanted ‘beard’. Iron filings stuck
to magnets can be removed with a stiff nail brush or even a
bristle doormat.
Display windows containing iron filings in fluid between two
plastic sheets are available from educational scientific
suppliers. These may have a white background for table
demonstrations or be completely transparent for demonstration
on an overhead projector (if you still have one). A third version
contains the filings in a transparent container with a central
tunnel for a magnet. It resembles a small kitchen roll. Slipping
a bar magnet into the tunnel produces a three-dimensional
field pattern.
A magnet display window.
The bar magnet can be inserted
into the central tube.
Avoid rubbing into eyes. Have eye wash facilities available. Pupils should only use only in sealed
containers.
48
Use iron rods to make electromagnets
Electricity flowing through a coil of wire produces a magnetic field. An
iron core in this field increases its strength. Wind plastic-coated wire
round a large iron nail. Connect the ends of the wire to a battery (use
only the cheap disposable type) to produce a magnetic field. It will
also heat the wire and run down the battery quickly, so only leave the
circuit connected for a few seconds at a time.
Using an iron nail to make
an electromagnet.
Do not use rechargeable batteries.
Use steel to demonstrate rusting as an example of chemical change
Try cooking oil or petroleum jelly for rusting
investigations in class. The paper clips on the left
were coated with petroleum jelly before water
was placed in the dish for a few days; those on
the right were untreated. The coated clips do not
appear to have rusted. Try this out yourself first:
some paper clips are plated (see below).
Rusting is a permanent chemical change due to the oxidation of iron or steel. It takes place in the
presence of air and water (or at least dampness). Water alone does not cause rusting. However,
objects can rust under water due to oxygen dissolved in it. Rust does not ‘leak’ from inside a metal
object; it is a surface effect. Iron pins or nails and steel wool will rust quickly due to their large
surface area. The chemical name for rust is iron(III) oxide. Coating or otherwise treating the iron
reduces and may even prevent rusting. Paint, copper plating, zinc coating and galvanising are used
in everyday life.
Take care with sharp edges. Count pins or nails out and in. If leaving for several days, it is helpful
to cover samples with a paper towel to keep dust and insects out.
Use metals for floating and sinking (density) activities.
Texts will suggest that a floating aluminium can or pie dish can
be crushed to show that aluminium sinks in water but in
practice extreme compression or even hammering is
necessary.
The picture shows items made from different materials in
water: the metal objects have sunk.
Take care with sharp edges.
49
Use aluminium to make mirrors
For light and reflection activities. A smooth sheet of foil reflects an
image. The same amount of light is reflected from a crumpled
sheet but it is sent back in various different directions, so no clear
image is formed.
The picture shows the difference between the reflections of an
object from fairly smooth or scrunched-up, aluminium, cooking foil.
Take care with sharp edges.
Use aluminium foil for cooking and heating activities
See advice on heating (section 2.4, Safe sources of heat and 2.5,
Heating and burning).
The picture shows aluminium foil used to hold samples during a
heating investigation.
Avoid contact with acidic foods, eg, lemon juice, tomatoes, vinegar, etc, which will corrode it.
Use metals as an important example of recycling
Aluminium is the third most common element on Earth but it is hard to get at. Extraction takes a
huge amount of electrical energy and 95% of this energy can be saved if aluminium is recycled
rather than extracted from ore. Iron is relatively cheap to extract but recycling will become more
economically worthwhile as fuel costs rise.
50
Oils, waxes and chemicals derived from oil
What are these substances? They are often referred to as mineral gases and oils. Products
separated from crude oil (petroleum). In this section we will consider a range of products from crude
oil, ranging from gases to solids. Many are chemically similar, although their physical properties
might be very different. We have divided them into three groups: (a) Butane, propane and piped gas;
(b) Mineral oils and (c) Wax.
(a) Butane, propane and piped gas
North Sea gas, used for domestic cooking and heating is
supplied piped by gas companies. Lighter and camping gases
are available from DIY stores and builders’ merchants.
What are they? Mineral gases from petroleum.
Most gas-filled lighters contain butane.
Butane or propane are contained in: Camping gas and lighter fuel. Butane may be a carrier in
aerosols.
Methane is the main constituent of piped gas (eg, North Sea gas), used domestically for cooking
and heating.
How safe is it?
Butane is an extremely flammable gas, stored under pressure as a liquid.
The gas can travel a considerable distance if released and may flash back if
ignited. It has been an abused solvent and can be dangerous if sprayed into
the mouth.
Camping or picnic stoves are not suitable for heating in the classroom. See
section 2.4 for guidance on safe heating methods.
Hazard label: HIGHLY FLAMMABLE.
Suitability: Teacher use for outdoor cooking only. A suitable risk assessment would be needed.
Use: Not for use in a science context. Do not use indoors. Gas cartridges, where used for outdoor
cooking, should only be changed outside, far away from naked flames. An appropriate risk
assessment would be needed.
Storage: For outdoor camping, store gas burners securely in a cool, well-ventilated place away from
combustibles and naked flames.
Disposal: Empty canisters may be accepted by your local recycling centre.
51
(b) Mineral oils
Petroleum jelly, medicinal paraffin, white spirit and
lubricating and engine oils are available from shops
including DIY stores and builders’ merchants.
What are mineral oils? These include petrol, paraffin,
white spirit 4, oils and thick liquids such as lubricating oil,
engine oil, medicinal paraffin, petroleum jelly 5, tar and solids
such as bitumen.
They may be mixtures and include other additives. Petroleum jelly (eg, Vaseline®) is a translucent
semi-solid mixture of oils. It is used as an ointment or lubricant. Lubricating and engine oils may
contain additives.
Mineral oils are also known as: In the USA, petrol is called gasoline, and liquid paraffin (which is
used as a fuel) is called kerosine. Vaseline is a brand of petroleum jelly. Medicinal paraffin is also
called paraffin oil. 3-in-1 and WD40 are brands of lubricating oil. Most of these products include
additives.
Mineral oils are found in: oil-based paints, some cleaning products and other ‘solvent-based’
products.
How safe are
they?
The hazards vary. Generally, the lighter the oil, the more likely it is to be
HIGHLY FLAMMABLE. Some oils have other hazards.
Hazard label: Check the label and see How safe is it? Some liquids are HARMFUL BY INHALATION
or INGESTION.
Suitability: Varies depending on the hazard. For low hazard oils, pupil use with supervision.
Always use a lower-hazard alternative if available.
Use: Take care with sensitive skins: disposable gloves should be worn. Eye protection is needed
when using any oil with a hazard label.
Storage: HIGHLY or EXTREMELY FLAMMABLE liquids require special storage and are unlikely to be
used in schools. For outdoor camping, store gas burners securely in a cool well-ventilated place
away from combustibles and naked flames.
Disposal: Small quantities of oils, medicinal paraffin or petroleum jelly may be mixed with plenty
of detergent (washing-up liquid) and flushed down a drain. Note that over time some oils may
combine with oxygen in air, becoming hot or even igniting. While not a petroleum product, linseed
oil left on rags has been known to ignite. Dampen rags soiled with such oils before bagging them
for disposal.
4
Turpentine is similar but it is derived from wood.
5
Vaseline was patented by Robert Cheeseborough in 1872. He purified residues considered inconvenient waste on
oil rigs but recognised by workers for its healing properties.
52
Activities using mineral oils
Use petroleum jelly for waterproofing
Some materials can be waterproofed (permanently but messily) with petroleum jelly. Spread it, for
example, on rags or paper used to make model umbrellas or roofs. See also Use steel to
demonstrate rusting as an example of chemical change under Metals.
Clear up spills using warm water with washing-up liquid.
Use petroleum products for lubrication
Pupils’ models and syringes used in hydraulic models (when two or more syringes are connected
with tight-fitting, water-filled plastic tube) can be lubricated with petroleum jelly. More delicate
equipment, locks, etc, need lubricating oil. WD40 contains a solvent and should be used by
teachers only.
Take care with sensitive skins.
Using oil-based paints
Small pots of, for example, enamel paints are sometimes used for painting models to give a glossy
finish. The same effect can be achieved using water-based varnish on top of water-based paint. If a
waterproof finish is needed, water-based paints could be used and, the teacher could apply a
waterproof varnish. Acrylic paints are water based and a range of bright colours is available.
See Cleaning oily stains and spills below for advice on cleaning.
Oil-based paints: Close supervision; only use small amounts in suitable containers. Good
ventilation is essential and no naked flames should be in the vicinity. Take care with sensitive skins:
disposable gloves should be worn. Household gloss paints in larger quantities should be teacher
use only.
Cleaning oily stains and spills
Petroleum products do not dissolve in water. Some are
good solvents for cleaning oily stains, eg, oil paints.
Medicinal paraffin can be used by pupils.
Oils and petroleum jelly might be removed from clothes or
skin with plenty of detergent or soap and water.
White spirit is commonly used to clean paintbrushes. This
should only be used by the teacher.
Take care with sensitive skins.
53
(c) Wax
Available as candles and tea lights.
What is wax? A solid oily mixture of animal, vegetable or mineral
origin. Paraffin wax, used for most candles, is a mineral wax.
Different types start to melt above 40 °C or 50 °C. Incidentally,
beeswax (which is not a mineral product) melts above 62 °C.
Wax is contained in: many types of candles and tea lights (‘night lights’).
How safe is it?
The wax is low hazard but when burning candles, or using melted wax, long
hair should be tied back and loose clothing tucked away. Do not carry
burning candles around. Melted wax is hot. It can drip or pour onto skin.
Position candles securely, away from combustible materials such as paper.
Suitable stands are available from educational scientific suppliers, or tea
lights can be placed in metal sand trays.
Hazard label: None.
Suitability: Pupil use: close supervision if heating or burning.
Use: Normal ventilation if heating / burning.
Disposal: Allow to solidify if melted then wrap and place in the normal refuse.
Activities using wax
Use wax to explore the effect of (moderate) heat on materials, a physical change
Wax softens and melts in hot water and can be shaped. This is a physical
change. This characteristic is used in ‘candle-making kits’, although the
wax is melted (gently) in a container without water for making candles or
wax-resist dyeing.
In the picture, melted wax has been reshaped before it cooled.
With care the original shapes could be reformed, demonstrating that these are physical changes.
Compare this to burning (see below) which is a chemical change.
Take care with hot water. Use a kettle and check the temperature is well below 60 °C.
Use wax to demonstrate burning and irreversible change
Tea lights are more stable than domestic candles. Children can
experience a burning candle safely at close range, learn that the candle is
a solid fuel and understand that a burning candle emits both heat and
light. Burning is a permanent, irreversible change; the wax burns away.
Pupil use: close supervision. No loose hair or clothing. Do not carry burning candles around. See
sections 2.5 and 2.6.
54
Observe the burning of a tea light closely
Use vocabulary such as candle, wax, wick, light, flame, burn (and
appropriate colours) and observe and describe the colours in a
candle flame: the bluish, unburned, candle wax gas and the yellow /
orange burning wax (see below for other observations). When a
candle or tea light burns, the exposed wick becomes longer and
begins to smoke. The longer the wick, the larger the flame and the
faster the candle burns away.
Children can observe and describe the black soot produced at the tip of the flame. Hot wax runs
and is liquid. Very hot wax rises and is a gas. Notice how the wick burns away outside the flame 6.
In the picture the tea light is floating in water.
Pupil use: close supervision. No loose hair or clothing. Do not carry candles around.
Use well-secured tea lights as a source of heat
Some science suppliers provide sturdy bent metal stands which
hold a tea light. Materials to heat and melt, eg, chocolate, fats or
wax itself can be put in a metal dish and placed on the shelf above
the flame. See section 2.4 for alternative safe sources of heat.
Pupil use: close supervision. No loose hair or clothing. Do not carry candles around.
Making candles and exploring variables
Properly supervised, pupils could make their own candles using wax granules and moulds. Kits and
supplies are available from educational suppliers, often in the arts or crafts section of the catalogue.
Finished candles can be burned and pupils could compare the burning rates for differently-shaped
candles.
Pupil use: close supervision. Use safe heating sources (see sections 2.5 and 2.6). No loose hair or
clothing. Do not carry candles around. Protect surfaces from heat damage and drips and spills.
6
The longer the wick, the larger the flame and the faster the candle will burn away. Historically, special cutters were
used to trim the wick but in 1825 a monk named Cambacéres invented a wick that bends over: he plaited the wick
tightly, producing a natural curve. The curve is held out straight by the candle wax until the wick is exposed. Burning
the wick accentuates the curve and allows it to poke out of the unburned gas into the air, where the tip burns away.
The black part of the wick inside the candle flame is not exposed to air, so it only chars slowly. In this way, most
modern candles have a self-trimming wick.
55
Wax as a translucent material
A lamp is placed behind a sheet of black paper and shines through the ‘pinhole’ pierced through it.
The pictures show that light is clearly visible through both a disc of wax and a polythene bag but
details of the picture cannot be seen so clearly through the wax. The polythene is transparent; the
wax is translucent.
Pupil use: close supervision. Make sure the paper is well secured and far enough from the light
source to avoid overheating. The lamp used in the photographs had an LED light source that is
cooler than other types, enabling it to be placed closer to the paper.
Wax-resist artwork
Water-based paints and dyes will not ‘take’ to a waxed surface. Use lumps of candle wax or wax
crayons to draw a design on paper then paint over the whole sheet. The waxed areas will remain
uncoloured. For wax-resist dyeing, use low temperature wax substitutes. These are available from
the arts and craft sections of education suppliers’ catalogues.
Pupil use: normal supervision.
56
Plaster of Paris
Available from educational suppliers, builders’ merchants and
craft shops, as a powder or impregnated into bandage (Modroc).
What is plaster of Paris? Anhydrous calcium sulfate. When
mixed with water, a chemical change happens, producing
hydrated calcium sulfate (the solid form), allowing casts to be
taken.
The picture shows an impression of a twig in plaster of Paris.
Plaster of Paris is contained in: Modroc.
How safe is it?
Plaster of Paris reacts exothermically with water, ie, the reaction produces
heat. In bulk, its temperature can reach above 55 °C. So it is important that
children do not attempt to make casts of their fingers or other body
parts by surrounding the part in plaster. It will expand and trap the
finger and simultaneously heat it. To make casts of fingers etc. lay the
finger in a shallow tray of plaster no more than 1 cm deep. This way the
finger can be lifted away as the plaster begins to set. Alternatively make a
cast in soft modelling clay, as described below.
Activities can be very messy. Wear disposable gloves to avoid skin irritation if
using large quantities or the activity is prolonged. Wash hands after use.
Hazard label: None but see How safe is it? above.
Suitability: Pupil use: close supervision.
Use: Take care with sensitive skins: disposable gloves should be worn.
Disposal: Wrap and place in the normal refuse. Do not pour down the sink where it would harden
and could clog the drainage system.
Activities using plaster of Paris
Use plaster of Paris for casting
Children can make casts of fossils, bones and other hard objects
by pressing them into soft modelling clay to make a mould. They
can cast hollow objects directly (shoe prints or animal tracks for
example). Pour liquid plaster of Paris into the mould and allow it
to set. Children can scratch identifying initials into the setting
plaster cast, and paint it with water paint when fully set. It may
take several hours to set completely.
Take care with sensitive skins: disposable gloves should be worn. Moulds of body parts can be
safely made with alginate, a flexible moulding compound sometimes used in dentistry.
57
Use plaster of Paris to demonstrate permanent change
Plaster of Paris is unusual in that it reacts exothermically with water - the reaction produces heat.
Many chemical reactions are endothermic - heating causes or speeds them.
Take care with sensitive skins: use disposable gloves as appropriate.
Use plaster of Paris for sheet-modelling landscapes, etc.
Plaster-impregnated bandage (Modroc) can be used to create a landscape or sculpture over a wire
frame. The strips are dipped in water then applied to the frame or shape and allowed to set.
It is important that children do not attempt to wrap their fingers or other body parts.
Take care with sensitive skins: use disposable gloves as appropriate.
58
Plastics
Plastics are defined as ‘polymers’ by chemists. These are long molecules made from repeating
units. Synthetic fibres are also types of polymer. We have written about polystyrene separately as
there are several activities for which it is particularly useful.
(a) Polystyrene
Available as scrap packing material or from educational
suppliers.
What is polystyrene? A hard type of plastic. Expanded
polystyrene is produced by bubbling air through the liquid
polystyrene before it cools and hardens, making it thicker and
opaque.
The picture shows polystyrene cups. The thick one is made from
expanded polystyrene.
Polystyrene is contained in: Disposable tableware. Thin cups are often made from non-expanded
polystyrene.
How safe is it?
Polystyrene is not chemically hazardous but see Use below.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use: Avoid use with children who may put small pieces into their nostrils and other orifices. Cutting:
Older pupils with good supervision or teacher use only, in well-ventilated areas. Cutting expanded
polystyrene, particularly with a junior hacksaw, produces quite a lot of dust. This mainly consists of
large enough particles to settle but is very messy to clear up. Cutting with hot wire cutters produces
vapours that, while not in harmful quantities if only one or two cutters are operating, have an
unpleasant smell. Ensure the room is well ventilated if using hot-wire cutters. Sanding with glass
paper produces a copious amount of dust. These processes could be carried out on a reasonably
small scale with good ventilation but avoid strong draughts. Samples should not be burned
Disposal: Recycle if possible or place in normal refuse.
Activities using expanded polystyrene
Use it for modelling
The low density of expanded polystyrene makes it useful for making large models that are not too
heavy.
Cutting: Older pupils with good supervision or teacher use only, in well-ventilated areas. Large
pieces of polystyrene are difficult to work: the depth to which they can be cut depends on the size
of the hacksaw or knife, and once cut there is a temptation to allow the rest to break off, producing
a very rough edge and a lot of dust. Cutting with hot wire cutters produces vapours that, while not in
harmful quantities if only one or two cutters are operating, have an unpleasant smell. See guide
L111, Tools and techniques.
Using cut pieces or shapes: Pupil use: not with children that may put pieces in body orifices.
59
Use expanded polystyrene to demonstrate thermal insulation
Expanded polystyrene is a good thermal insulator (poor
conductor of heat). It contains bubbles of trapped air that do not
conduct heat well. Therefore, unlike metals, which conduct heat
well, it doesn’t take heat away from a warm hand to make it feel
cold. Polystyrene feels warm to the touch and even reflects
hand-heat from a short distance.
Use expanded polystyrene to make shapes for testing air and water resistance
Children can make small boats with bows of different shapes from expanded polystyrene. They will
find that ‘streamlined’ shapes are easier to move and can pull each boat through water to compare
streamlining efficiency.
Cutting: Older pupils with good supervision or teacher use only, in well-ventilated areas. Large
pieces of polystyrene are difficult to work: the depth to which they can be cut depends on the size
of the hacksaw or knife, and once cut there is a temptation to allow the rest to break off, producing
a very rough edge and a lot of dust. Cutting with hot wire cutters produces vapours that, while not in
harmful quantities if only one or two cutters are operating, have an unpleasant smell. See guide
L111, Tools and techniques.
Using cut pieces or shapes: Pupil use: not with children who may put pieces in body orifices.
(b) Plastics: other types
Widely available, depending on the type and use.
What are these plastics? A huge range of polymers. Their
properties and therefore their uses vary considerably.
The picture shows objects made from various plastics.
Plastics are contained in: See the table below for names, properties and typical uses.
How safe are
they?
Plastics are not chemically hazardous but see Use below.
Hazard label: None.
Suitability: Pupil use: normal supervision.
Use:
•
Avoid using small pieces with children who may eat them or put them into body orifices.
•
Molten plastic clings to the skin and can result in a bad burn.
•
Several plastics give off hazardous fumes when they burn. Only tiny samples, no larger than a
rice grain should be burned over a metal tray to catch drips. Ensure the room is well ventilated
when heating small samples. Do not burn PVC. Have a supply of water to hand in case of burns
to skin.
•
Some plastics dissolve in certain solvents; check suitability before using with glues.
Disposal: Recycle if possible or place in the normal refuse.
60
Plastics - names, properties and uses
Common name
Other names
Some properties and uses
Nylon
-
Can be quite strong. Clothes, gears, bearings, textiles.
Perspex
Acrylic,
polymethlymethacrylate
Strong and rigid. Glazing.
PET
Polyethylene
terephthalate
Lemonade & similar bottles. Sometimes recycled as the
fibres in fleeces.
Polycarbonate
-
Transparent glazing materials as an alternative to glass
used, eg, for bottles.
Polyester
-
Can be drawn into threads. Textiles, clear resins.
Polypropylene
Polypropene
Containers, laboratory ware, ropes, carpet fibres.
Polystyrene
-
Disposable containers.
Expanded
polystyrene
-
Packing.
Polythene
Polyethylene, polyethane
Can be made into flexible sheets. Containers, pipes, hotmelt glue.
Polyurethane
-
Foam in furniture, insulation, etc.
PVC*
Polyvinyl chloride
Wide range. PVC can be very flexible or quite rigid
depending on how much plasticiser is added. Aprons,
drain pipes & gutters are often made from it.
Teflon*
PTFE,
polytetrafluoroethylene
Non-stick coating, bearings.
Terylene
-
Can be drawn into threads. Textiles.
UPVC*
Unplasticised PVC
Plastic window frames.
* These should not be heated in primary schools.
Activities using plastics
Test the effect of heat on materials
For polythene, polystyrene, polypropylene, perspex or nylon,
use tiny samples no larger than a rice grain and heat them
over a metal tray to catch drips.
Teacher demonstration only; see section 2.5. Do not burn PVC, polyurethane or PTFE (used in
non-stick cookware) as their fumes are particularly hazardous. Molten plastic clings to the skin and
can result in a bad burn. Ensure the room is well ventilated when heating small samples. Have a
supply of water to hand in case of burns or eye injuries.
61
Use plastics to investigate other properties of materials
A number of properties can be investigated and used to compare materials. For example you can
test their:
•
strength by loading plastic bags or testing strips cut from plastic bags,
•
ease of cutting: see guide L111, Tools and techniques for suitable methods,
•
bending samples,
•
floating: polythene and expanded polystyrene float on water; other types sink unless shaped
appropriately (like boats),
•
stretching and twisting strips, loading plastic straws,
•
smoothness of surface using friction activities.
Supervise children to make sure they don’t apply too much force when bending samples. Flexible
or semi-rigid materials such as polythene are suitable; rigid samples that can produce sharp edges
if they break should be avoided. Take usual care with tools and water.
Use plastics as examples of materials that can be recycled
The recycling symbol will be accompanied by a recycling number, eg, 1 for PET, a
common bottle material or 3 for PVC.
62
Salts
Available from pharmacies and shops.
What are salts? Compounds consisting of two types of
substance chemically bound together. There is a huge variety of
salts with widely differing properties. Common salt, whose
chemical name is sodium chloride, is a component of all living
tissues. It is also found in seawater, from which it has been
extracted for centuries. The name of ‘Epsom salts’ derives from a
saline spring in Epsom, Surrey; they are a mild relaxant and
laxative; also added to baths to soothe the skin.
Also known as: Common salt is sodium chloride. Epsom salts is magnesium sulfate. Cream of
Tartar is potassium hydrogen tartrate. Water glass, used in past times as a preservative, is sodium
silicate (and can be used to make crystal gardens). Alum (aluminium potassium sulfate) can be
grown in a crystal garden.
Salts are contained in: foods, soil and composts, cleaning fluids and many other household
products.
How safe are
salts?
Household salts are generally not classified as hazardous but check the label
and avoid spills on the skin or eyes.
Hazard label: Common salt, alum and Epsom salts are low hazard (though common salt can sting
open wounds and Epsom salts is a purgative). Water glass diluted for use is IRRITANT but a
concentrated solution is CORROSIVE.
Suitability: Pupil use: close supervision. Avoid use with children that may eat salts.
Use: Avoid raising dusts. Take care with sensitive skins.
Disposal: Wrap and place in normal refuse or dissolve and flush away.
Activities using salts
Use salts to make crystals by dissolving and evaporation
Make a concentrated solution and allow the water to evaporate
in a low, wide container in a warm, well-ventilated place. The
crystals of different salts have different shapes. See Sugar and
sweeteners for details of making big sugar crystals.
To make a crystal garden, use sodium silicate solution. It may
be easier to purchase a kit.
The picture shows crystals of ammonium dihydrogenphosphate,
a substance similar to Cream of Tartar.
Avoid splashing the eyes. Take care with sensitive skins.
63
Soaps and cleaning products
Available from shops and pharmacies.
What are they? Soaps and detergents are
processed animal, mineral or plant fats. They are
cleaning agents, active on surfaces because their
molecules have a ‘tail’ that penetrates oil or grease
drops, while their ‘heads’ are soluble in water. Dirt is
held in the natural film of grease on hands and other
parts of the body. The ‘tails’ of soap or detergent
molecules become attached to the greasy dirt while
the ‘heads’ are attracted to water.
Groups of these combined particles can clump together, remain in suspension and are washed
away with the dirt. Biological detergents include enzymes that break down specific food
components. Soaps (technically detergents derived from animal or vegetable oils) can also react
with chemicals in hard water to make insoluble substances, producing scum.
Bleaches are chemically active substances that destroy germs and can react with colour
molecules, ‘bleaching’ them. Disinfectants can be used on non-living tissues and remove some
germs; antiseptics do the same job and are safe to use on living tissue.
Soaps and detergents are found in: Washing-up liquids, eg, Fairy™ Liquid, cleaning fluids,
shower gels, tooth pastes, washing powders and dishwasher powders (though this usually includes
CORROSIVE or IRRITANT substances).
Bleaches and disinfectants are found in: Branded products, eg, Dettol, Dettox, Milton’s fluids,
Domestos, Harpic, Vortex, some antibacterial products (though some may contain alcohol instead of
or in addition to an antiseptic). Note that some of these products may contain other additives, eg,
detergents, perfume and something to make them taste nasty.
How safe are
cleaning
products?
Products made for use on the skin should be safe if used as directed, although
some people may be sensitive or have allergies to some components. These
weak alkalis degrease the skin and may affect children with sensitive skins. Avoid
splashing detergent solution in the eyes. Other detergents are not suitable for
pupil use, especially dishwasher and biological detergents.
Bleach is one of the most dangerous household substances and must be handled
with care. NEVER mix bleaches with other cleaners or with acids. Chlorine, a
choking TOXIC gas, may be produced. Bleaches may be based on chlorine or
oxygen. The former contain sodium chlorate(I) [sodium hypochlorite (NaClO)] or
another substance that releases chlorine when dissolved in water. Oxygen-based
bleaches may contain hydrogen peroxide or a substance that releases a
peroxide. Depending on concentration, all these products may be CORROSIVE or
IRRITANT: read the label on the packaging. Disinfectants and antiseptics may
contain a variety of ingredients. Check the label and use as directed.
Bleaches, disinfectants and antiseptics have limited shelf lives, particularly after
dilution. Dilute freshly before each use. Diluted soaps and detergents could also
allow bacterial growth if left for long periods. Viruses and bacterial spores tend to
be less susceptible than most bacteria to these products. Washing with soap (or
detergent) and water removes most germs with the dirt and is good front-line
defence against the spread of infections, unless sterile conditions are needed.
Washing soda [sodium carbonate (Na2CO3)] is IRRITANTATING TO EYES.
64
Hazard label: May be CORROSIVE or IRRITANT and HARMFUL: read the label.
Suitability: Pupil use: Soaps and detergents: normal supervision. Bleaches, disinfectants and
antiseptics: products should be diluted for use then used with close supervision. Note that at the
stated dilution of Milton’s fluid, at least 30 minutes contact time is needed. Washing soda: Teacher
use only.
Use: Avoid splashing eyes. Take care with sensitive skins. See also section 2.7.
Disposal: Dilute and flush away or wrap and place in normal refuse.
Activities using detergents
Use detergent to break the surface tension on water
The pin was lowered carefully
onto the surface of some
coloured water. It appears to be
‘sitting’ on a ‘skin’ on the water,
caused by surface tension.
You can make a metal pin float. Use a very clean bowl (with no
trace of detergent on it), some water, a pin or paperclip and a
small piece of paper towel. Fill the bowl three-quarters full of
water. Put the pin or paperclip on a small piece of paper towel to
act as a ‘raft’. Gently lower the ‘raft’ into the water; the pin will
float as the waterlogged paper sinks. Touching the edge of the
water with a tiny drop of washing up liquid will destroy the
surface tension and the pin will also sink.
Pond-skaters walk on the ‘skin’ of water produced by surface
tension. The demonstration suggests how damaging detergents
can be in the environment.
Avoid splashing the eyes.
Use safe detergents for washing-up and washing comparisons
Compare cold water, hot water, cold water with detergent, and hot water with detergent. How well
does each remove a standard stain from a plate? Similar comparisons can be made using samples
of fabrics to which various stains have been applied.
Avoid splashing the eyes and take care with sensitive skins.
Activities using shaving foam and hair mousse
Use shaving foam or hair mousse to demonstrate interesting mixtures
Shaving foam and hair mousses are liquid-in-gas foams.
Over time, the air bubbles ‘pop’ and the foam ‘flattens’.
Avoid splashing the eyes.
65
Sugars and sweeteners
Sugars are usually sweet-tasting carbohydrates. Common
sugar is sucrose, found in the pith of sugar cane and sugar
beets. Sold as cubes, granulated, caster, icing and brown
sugars.
The simple sugar glucose is available from pharmacies and
health food shops. Fruits contain other sugars, eg, fructose.
Honey contains both glucose and fructose. Golden syrup is
treated cane sugar. It contains a mixture of sugars.
Drinks such as tea and coffee contain caffeine, a stimulant drug. See also Cola.
Saccharin, aspartame, sucralose, neotame and acesulfame potassium are artificial sweeteners,
with much greater sweetening power than equivalent quantities of sugar or corn syrup. Sorbitol and
xylitol are ‘natural’, vegetable-derived sweeteners, though commercial products are probably
produced artificially.
How safe are
they?
Ready-to-eat foods and drinks are generally low hazard but be aware of any
food sensitivities or allergies and keep en eye on children who may be
tempted to eat unsuitable quantities. Use low-caffeine versions if children are
to drink beverages in an activity. Artificial sweetener tablets may be better
avoided with very young children and young children with phenylketonuria
must avoid aspartame.
Some people are sensitive to lactose or allergic to cows’ milk. They may
tolerate milk from other animals (goats, sheep and others) or plant
formulations (soya, rice or oat). Some lactose-intolerant individuals can
tolerate some cheese or yoghurt, or milk treated with the enzyme lactase.
Always check before offering foods or drinks that may contain milk, whey or
lactose.
Hazard label: None. Suitability: Pupil use: supervision level depends on the activity.
Use: Take care with food sensitivities and allergies. If samples are to be eaten, take stringent
hygiene precautions and explain clearly that this is why they may, exceptionally, eat in a science
lesson!
Disposal: With the normal refuse.
Storage: Store as appropriate and dispose of samples if no longer fresh.
66
Activities using sugars
Use sugars to demonstrate and investigate solutions
Icing sugar does not completely dissolve in water as it contains
calcium phosphate to prevent ‘caking’ so produces a cloudy
suspension.
Brown sugars can be preferable for dissolving investigations as
the solution is coloured and therefore more visible in water.
This activity is likely to be messy and leave sticky residues. Be prepared to clear up very thoroughly
and always wash hands well afterwards.
Use sugar to make big crystals
Sugar produces large (though sticky) crystals. Tie a wellshaped starter crystal (either bought from a specialist shop or
produced from sugar solution) on a hair, suspend it in a
saturated solution in a cup and leave it for a week or so in a
place where it won’t be disturbed.
The picture shows commercially-produced sugar crystals:
yours may be less spectacular!
Cover the solution to protect it from dust and insects. This activity is likely to be messy and leave
sticky residues. Clear up very thoroughly and wash hands well afterwards.
Use sugar or sweeteners in taste investigations
Make dilutions of solutions of sugars and sweeteners to compare their taste thresholds.
Observe scrupulous hygiene precautions and explain these to the pupils. Take care over diabetics
and children suffering from obesity or relevant food sensitivities. Dispense only the quantities
needed. Wash hands and clean surfaces well afterwards.
Activities using artificial sweeteners
Use artificial sweetener tablets to investigate rates of reactions
A Year 6 investigation in QCA Unit 6C suggests that you provide children with artificial sweeteners
and tell them that the manufacturer needs to know how long they take to dissolve in chilled water,
water at room temperature, warm and hot water.
Use alternatives with children who may ingest the tablets. Use brown sugar or see Bicarbonate of
soda for alternative rates of reaction activities. Dispense only the number needed. Take care over
diabetics and children suffering from obesity or relevant food sensitivities.
67
Activities using tea or coffee
Use tea to demonstrate that not all solutions are colourless
Showing children a cup of weak black tea both shows an
example of a non-colourless solution and also helps to
challenge the commonly-held misconception that dissolved
solids (like salt and sugar) ‘disappear’ when added to water.
The water is clear (transparent) but coloured brown.
The picture shows that writing can be seen (fairly) clearly
through a cup of tea without milk.
Supervise children to ensure they do not drink the tea.
Use coffee as a bitter taste in taste tests
Dissolve a small amount of decaffeinated coffee in water. Dispense only very small quantities and
show children how to taste a drop without drinking the coffee.
Supervise children to ensure they do not drink the coffee. Note that decaffeinated coffee still
contains a small amount of caffeine.
Use drinks as an example of an impure liquid
(2)
(1)
Allow a small amount of cola or lemonade to evaporate in a warm place and observe the residue.
Fruit juices and other soluble drinks will also show this effect. This is not related to the acidity of the
sample but to the fact that it isn’t pure water. Colourless, non sugar-free lemonade may give even
more convincing evidence that not all clear liquids are pure water, an important lesson when
teaching about safety and unknown substances!
The pictures show (1) that the sugars in cola might leave a syrupy residue when the water
evaporates, and (2) that even colourless diet lemonade isn’t pure (see the slight residue around the
edge of the bowl).
Do not eat or drink the samples. Leave them where they won’t be disturbed and cover them lightly
with a paper towel to keep insects away.
68
Soil and gardening products
Available from the garden or other ground, or bagged as compost. Potting
‘composts’ and other gardening products are available from garden centres
and shops.
What is soil? A mixture of ground rock fragments of different types and
organic matter produced from the decay of animal and plant remains. The
type of soil depends on the relative composition of, eg, clay, sand and
organic material. Technically, compost is plant material that has rotted but
a number of plant growing media based on either compost or other bases
are available for growing plants. Fertilisers and ‘plant foods’ contain
some, or all, of the twenty or so chemical trace elements necessary for
healthy plant growth, and to compensate for poor soil. Brand names
include Baby Bio, Phostrogen, Tomorite®, etc.
The top picture shows London garden soil. The soil in the centre picture is
sandy. The bottom picture shows potting compost, containing a variety of
additives.
Also known as: Potting compost, John Innes, loam.
How safe are soils
and other
gardening
products?
Soil is a natural product in the environment. The main hazards are from
contamination and from some natural organisms found in it. Plant growing
media may have been sterilised during manufacture, although it would not
remain sterile once the pack has been opened.
Some additives for use with soils and some garden products may be
hazardous. Always read the label.
Hazard label: Soil and most plant growing media: none.
Suitability: Pupil use: normal supervision. Products with hazard classifications: Teacher use or
Pupil use: only with close supervision.
Use: Do not use soil samples likely to be contaminated with sharp or other dangerous objects or
with animal urine, faeces or other products. Cover open wounds when handling soil and wash hands
thoroughly with soap and water afterwards. Supervise children to ensure this is done properly.
Foods and drinks should be kept and handled separately from soil.
Storage: Check the label on any products used and store securely. Soils should be stored in a cool,
dark place with some ventilation. Damp, airless conditions encourage mould growth; it may be better
to allow soils to dry out and to add water before use, though some types of compost are more
difficult to reconstitute than others.
Disposal: Products without chemical hazards: wrap and place in normal refuse. Hazardous
chemicals: recently-purchased products: dilute as directed for use and flush away with further
dilution. Old or unidentified products: call CLEAPSS for advice.
69
Activities using soils and fertilisers
Comparisons of different types of soils
Soil texture depends on the size of the grains in the soil. Grains can be made from clay (the
smallest), sand (the largest), or silt (medium sized). Soils are classified as clay, silty or sandy.
Loam soils, a fairly even mix of clay, silt, and sand particles are the best for plant growth. Some
plants prefer acidic or alkaline soils. Some can tolerate high levels of salt. Pupils can observe that
different soils have different structures, test them for acidity and identify why particular soils are
chosen for particular uses. The pictures show salt-tolerant plants on a sandy beach and acid-loving
heather.
Pupil use; normal supervision. Wash hands after use even if gloves are worn. Warn pupils to avoid
rubbing their eyes or put their fingers into their mouth.
Use soil to explore speed of drainage
Plants grow best in soils with drainage rates that best match their needs.
Pouring water through measured samples of soils gives an idea of their
drainage rates and capacities. Poorly draining soils generally retain the most
water while well-drained soils usually allow more water to pass through.
Although sand drains quickly it does not retain enough water for most plants
to grow. Mixed soils suit a wider range of plants, although some plants prefer
desert conditions while others thrive when waterlogged. Remember too, that
the fertility of soil is a key factor in the growth of plants.
Pupil use: normal supervision. Wash hands after use, even if gloves are worn. Warn pupils to avoid
rubbing their eyes or put their fingers into their mouth. Have a supply of water handy in case
irrigation is needed.
70
Testing soils for acidity
Soil testing kits are available from garden centres and
educational suppliers. They test the pH - a measure of how
acidic or alkaline a sample is (see Make and use an indicator
under Acids).
Many plants grow better in acidic or alkaline soils. The type of
plant that thrives in a soil can demonstrate whether it is acidic or
alkaline. Sphagnum moss peat makes soil more acid; some
chalks make soil alkaline.
Follow the instructions carefully. Always supervise children’s hand washing after handling soil, even
if gloves are worn. Hazardous materials should carry a warning symbol: check their suitability in
section 1.3 Chemical hazard warning symbols.
Use fertiliser to demonstrate plants need traces of chemicals for healthy growth
Plants make their own food by photosynthesis using carbon dioxide from the air, water and energy
from sunlight but trace amounts of mineral salts present in most soils and in fertilisers are essential
to healthy growth. (Carnivorous plants growing in poor soils supplement their mineral intake by
trapping insects). The name ‘plant food’ is a misnomer that can lead to confusion. Observing, eg,
geranium cuttings kept in water for a few days, can show that plants get their energy from sunlight.
However, comparing the growth of two sets of seedlings planted together, one with and one without
added fertiliser, can show that plants need these trace nutrients for long-term healthy growth.
Follow the instructions on the container.
71
5 Chemical Index
In this index we list chemical names. We have included the majority of chemicals you might use or
want to use and also some you might find lurking in a corner that you probably should not use. We
have also included alternative names where these are in common use. Where appropriate, safety or
other information is provided in column 3. Also in column 3 are references, in italics, to relevant
topics in section 4 of this guide. Contact CLEAPSS for advice on disposal of any unwanted chemical
with a hazard warning.
Chemical
Alternative name(s)
Brief notes and references to chemicals
in section 4
Acesulfame
-
Sugars and sweeteners.
Acetic acid
Ethanoic acid.
-
Acetone
Propanone.
-
Aftershave
-
Soaps and cleaning products.
Alcohol, denatured
Ethanol.
-
Alka Seltzer®
-
Contain aspirin, bicarbonate of soda (a weak
alkali) and citric acid. See Baking chemicals
for alternatives.
Alum
Aluminium potassium sulfate;
potassium aluminium sulfate.
Other alums exist. Chrome alum and ferric
alum are IRRITANT. Salts.
Aluminium block
-
Metals.
Aluminium foil
Cooking foil.
Metals.
Aluminium potassium
sulfate
Alum.
-
Anhydrous
-
Refers to a dehydrated form of a chemical, not
a chemical in its own right. Look under the
main entry for the chemical.
Antibacterial cleaner
-
Soaps and cleaning products.
Antibacterial hand
rub
-
Soaps and cleaning products.
Antiseptic
-
Soaps and cleaning products.
Aspartame
-
Sugars and Sweeteners.
Baby Bio
-
Soils and gardening products.
Baking powder
-
Contains bicarbonate of soda (a weak alkali)
with cream of Tartar and/or other additives,
possibly derived from wheat. Baking
chemicals.
Baking soda
Sodium hydrogencarbonate.
-
Balsa cement
-
Look under ‘Cement, balsa’.
Bath bombs
-
Contain a weak alkali. Baking chemicals.
Bicarbonate of Soda
Sodium hydrogencarbonate.
-
72
Bitumen
-
Not suitable for use in primary science. Oils,
waxes and chemicals derived from oil.
Bleach
May contain sodium
chlorate(I).
May be an alkali. Neat bleaches may be
CORROSIVE and are not suitable for use by
primary pupils.
Borax
Sodium tetraborate.
-
Bottled gas
Camping gas; butane or
propane.
-
Brass
-
Metals.
Butane
Bottled gas, lighter fuel.
EXTREMELY FLAMMABLE. Oils, waxes and
chemicals derived from oil.
Calcite
Calcium carbonate.
-
Calcium carbonate
Limestone; marble chips;
some blackboard chalks;
calcite.
Calcium carbonate.
Calcium sulfate
-
Plaster of Paris.
Candles
Oils, waxes and chemicals derived from oil.
Caustic soda
Sodium hydroxide.
-
Cellulose paste
Starch-based paste;
wallpaper paste.
Use fungicide-free versions. Glues.
Cement, balsa
Balsa cement.
The word ‘cement’ is sometimes used for
other adhesives. Glues.
Cement, Portland
-
IRRITANT. A strong alkali. Cement and
concrete.
Chalk, blackboard
-
Calcium carbonate.
Charcoal
Drawing charcoal is impure carbon.
Citric acid
2-hydroxypropane-1,2,3tricarboxylic acid.
A weak acid. Crystals and solutions 20% and
above are IRRITANT. Acids.
Clay
-
Clay and modelling materials.
Coca Cola
-
Look under ‘Cola drink’.
Coffee, instant
-
Contains caffeine (even decaffeinated
versions contain a small amount). Sugars and
sweeteners.
Cola drink
-
A weak acid. Acids.
Compost
-
Soils and gardening products.
Concrete, dry,
ready-mix
Contains Cement, Portland.
-
Cooking foil
Aluminium foil.
-
Cooking oil
-
Cooking oils and fats.
Copper, block
-
Metals.
Cornflour
-
Baking chemicals.
73
Cream of Tartar
Potassium hydrogentartrate.
-
Crude oil
Petroleum.
TOXIC. Banned for school use. Oils, waxes and
chemicals derived from oil.
Detergents
Washing-up liquids; washing
powders.
May be alkalis. Soaps and cleaning products.
Dishwasher
detergent
-
Contains strong alkali. Not suitable for use by
primary pupils.
Disinfectant
-
Soaps and cleaning products.
Duplicating fluid
Ethanol, denatured or
methanol.
HIGHLY FLAMMABLE and may be HARMFUL or
TOXIC. Contact CLEAPSS for advice on
disposal.
Engine oil
-
May be HARMFUL. Teacher use only. Oils,
waxes and chemicals derived from oil.
Epsom salts
Magnesium sulfate.
-
Ethanoic acid
Acetic acid; found in vinegar.
A weak acid. Concentrated ethanoic acid and
solutions above 25% are CORROSIVE.
Solutions 10-25% (at least 0.8 M) are
IRRITANT. Use more dilute solutions eg,
vinegar. Acids.
Ethanol
Impure forms include
Industrial Denatured Alcohol;
IDA, methylated spirits; meths
[used to be called Industrial
Methylated Spirits (IMS)].
HIGHLY FLAMMABLE and HARMFUL. Contained
Fertilisers
Plant ‘foods’ eg, Baby Bio;
Tomorite; Phostrogen.
Soils and gardening products.
Flour
-
Baking chemicals.
Food colours
-
Food additives.
Fructose
-
Sugars and sweeteners.
Fruit juice
-
Acids.
Gas, bottled
Butane or propane.
EXTREMELY FLAMMABLE. Oils, waxes and
in surgical spirit and some hand rubs, which
may be low hazard. Alcohols and other
solvents. Ethanol outside these products is not
suitable for primary school use. May be in
duplicating fluids. Contact CLEAPSS for
advice on disposal.
chemicals derived from oil.
Gas, North Sea
Heating / cooking gas; mainly
methane.
EXTREMELY FLAMMABLE. Oils, waxes and
Gasoline
Petrol.
-
Gelatine
-
Food additives.
Glucose
-
Sugars and sweeteners.
Glue, glue gun
-
Glues.
Glue, solvent-based
-
May be HIGHLY FLAMMABLE. Glues.
Glue, water-based
-
Glues.
Glycerine
Glycerol.
Food additives.
74
chemicals derived from oil.
Hand rub / gel
May contain ethanol or
propan-1,2-ol.
-
Helium
-
Helium.
Hydrochloric acid
-
CORROSIVE above 25%; IRRITANT 10-25%
(may be labelled 2 M). Contact CLEAPSS for
advice on use or disposal.
Icing sugar
Sucrose.
Sugars and sweeteners.
IDA / IMS
Industrial Denatured Alcohol.
-
Indigestion tablets
and other medicines
-
Some contain aspirin. Look under ‘Alka
Seltzer’ for more details.
Industrial Denatured
Alcohol (IDA)
Industrial Methylated Spirits;
IMS.
An impure form of ethanol sold for non-edible
use. Not suitable for use by primary pupils.
Look under ‘Ethanol’.
Industrial Methylated
Spirits (IMS)
Industrial Denatured Alcohol.
-
Instant mashed
potato
-
Baking chemicals.
Instant puddings
-
Baking chemicals.
Iodine, tincture of
-
Contains ethanol. May be HIGHLY
FLAMMABLE. Not suitable for use by primary
pupils. Alcohols and other solvents.
Iron filings
-
Metals.
Iron rod / nails
-
Metals.
Iron(III) oxide
Rust.
Metals.
Isopropanol
Propan-2-ol.
-
Jelly cubes or
crystals
-
Food additives.
John Innes
No 1, 2 & 3
Potting Compost.
Soils and gardening products.
Kerosene
Paraffin.
-
Lead block
-
TOXIC. Metals.
Lemon juice
Contains dilute citric acid.
Acids.
Lighter fuel
Butane or propane.
-
Linseed oil
-
A mixture of oils derived from flax seed, but
see the note on disposal in Oils, waxes and
chemicals derived from oil.
Litmus
-
An acid-alkali indictor. Acids.
Loam
-
Soils and gardening products.
Lubricating oil
-
May be HARMFUL. If so, not suitable for use by
primary pupils. Oils, waxes and chemicals
derived from oil.
75
Magnesium sulfate
Epsom salts.
Not classified as hazardous but it is a laxative.
Salts.
Marble
Contains calcium carbonate.
-
Medicinal paraffin
Paraffin, liquid.
-
Mercury
-
TOXIC. Mercury thermometers are not suitable
for primary schools. If spilled, consult
CLEAPSS.
Methane
-
Look under ‘Gas, North Sea’.
Methanol
-
HIGHLY FLAMMABLE and TOXIC. A component
of IDA. Was used as a duplicating fluid.
Contact CLEAPSS for advice on disposal.
Miltons
-
Diluted sodium chlorate(I) with other additives.
Soap and cleaning products.
Mineralised
methylated spirit
-
HIGHLY FLAMMABLE and HARMFUL. A more
Modroc
Contains plaster of Paris.
-
Nail varnish
May contain propanone.
-
Nail varnish remover
May contain propanone.
-
Nails, iron or steel
Iron, steel.
Metals.
Neotame
-
Look under ‘Sweeteners’.
Nickel
-
HARMFUL. Metals.
Nylon
-
Plastics.
Oils, for cooking
Cooking oil.
Cooking oils and fats.
Oils, mineral
Paraffin oils.
Oils, waxes and chemicals derived from oil.
Paraffin
Kerosene.
FLAMMABLE. Oils, waxes and chemicals
impure form of ethanol than Industrial
Denatured Alcohol. Not suitable for use by
primary pupils.
derived from oil.
Paraffin, liquid
Medicinal paraffin.
Do not confuse with paraffin (kerosene), which
is sometimes confusingly labelled ‘paraffin oil’.
Oils, waxes and chemicals derived from oil.
Pastes
-
Look under ‘Cellulose paste’.
Pepsi Cola
Cola drink.
-
Perspex
Polymethylmethacrylate.
Plastics.
Petrol
Gasoline.
EXTREMELY FLAMMABLE and HARMFUL. For
use only in internal combustion engines. See
Oils, waxes and chemicals derived from oil.
Petroleum
Crude oil.
-
Petroleum jelly
Vaseline.
Oils, waxes and chemicals derived from oil.
Phostrogen
-
Soils and gardening products.
Plain flour
-
Baking chemicals.
76
Plaster of Paris
Anhydrous calcium sulfate.
Plaster of Paris.
Plastic
-
There are many types. Plastics.
Polycel
Cellulose paste.
-
Polypropylene
Polypropene.
Plastics.
Polystyrene,
expanded
-
Plastics.
Polythene
Polyethene.
Plastics.
Portland cement
-
Look under ‘Cement, Portland’.
Potassium aluminium
sulfate
Alum.
-
Potassium
hydrogentartrate
Cream of Tartar.
A weak acid. Used in baking powder. Salts.
Potting compost
Compost.
Soils and gardening products.
Propan-2-ol
Isopropanol.
HIGHLY FLAMMABLE and IRRITANT. Hand rubs
may contain a dilute mixture and be low
hazard. Alcohols and other solvents.
Propane
Bottled gas; lighter fuel.
EXTREMELY FLAMMABLE. Oils, waxes and
chemicals derived from oil.
Propanone
Acetone.
HIGHLY FLAMMABLE and IRRITANT. Often
contained in nail varnish and nail-varnish
remover. Alcohols and other solvents.
Rust
Iron(III) oxide; hydrated
iron(III) oxide; ferric oxide.
Metals.
Saccharin tablets
-
Sweeteners.
Salad dressings
-
Look under ‘Ethanoic acid’.
Salt, common
Sodium chloride.
Salts.
Sand
-
Cement and concrete.
Self-raising flour
-
Baking chemicals.
Sherbet
-
Contains citric acid and bicarbonate of soda (a
weak alkali). Baking chemicals.
Soap
-
Soap and cleaning products.
Soda, baking
Bicarbonate of soda.
A weak alkali. Baking chemicals.
Soda, caustic
Sodium hydroxide.
-
Soda, washing
Sodium carbonate.
Soaps and cleaning products.
Sodium
hydrogencarbonate
Bicarbonate of soda; baking
soda, sodium bicarbonate.
-
Sodium bicarbonate
Bicarbonate of soda.
-
Sodium chlorate(I)
Sodium hypochlorite; used in
many bleaches.
Solutions above 10% available chlorine are
CORROSIVE; between 5% and 10% they are
IRRITANT. See section 2.7.
Sodium chloride
Common salt.
Salts.
77
Sodium
hydrogencarbonate
Bicarbonate of soda; baking
soda; sodium bicarbonate.
A weak alkali. Baking chemicals.
Sodium hydroxide
Caustic soda.
A strong alkali. CORROSIVE unless very dilute
[below 0.5% (0.05 M)]; it is IRRITANT between
0.5-5%). Use more suitable alternatives and
contact CLEAPSS for advice on disposal.
Sodium hypochlorite
Sodium chlorate(I).
-
Sodium silicate
Waterglass.
An alkali. Solutions above 5% are IRRITANT.
Salts.
Sodium tetraborate
Borax.
An alkali. TOXIC. See Glues.
Soil
-
Soils and gardening products.
Starch-based paste
Cellulose paste.
-
Sucralose
-
Look under ‘Sweeteners’.
Sucrose
Sugar (common).
Sugars and sweeteners.
Sugar, common
Sucrose.
Sugars and sweeteners.
Sulfuric acid
Sulphuric acid.
CORROSIVE above 15%; IRRITANT above 5%
(may be labelled 0.5 M). Contact CLEAPSS
for advice on use or disposal. See Acids for
suitable alternatives.
Surgical spirit
-
Contains ethanol. Alcohols and other solvents.
Sweeteners
-
Aspartame contains phenylalanine. Sugars
and sweeteners.
Tartar, cream of
Potassium hydrogentartrate.
Tea lights
-
Oils, waxes and chemicals derived from oil
Tomorite
-
Soils and gardening products.
Turpentine
-
FLAMMABLE and HARMFUL. Oils, waxes and
chemicals derived from oil.
Vaseline
Petroleum jelly.
Vinegar
Dilute ethanoic acid.
Acids.
Vitamin C
Ascorbic acid.
Food additives.
Wallpaper paste
Cellulose paste.
-
Washing-up liquids,
washing powders
Detergent.
-
Waterglass
Sodium silicate.
Look under ‘sodium silicate’.
Wax
-
Oils, waxes and chemicals derived from oil.
White spirit
-
FLAMMABLE and HARMFUL. Oils, waxes and
chemicals derived from oil.
Wire wool
Steel
Metals.
Yeast
Saccharomyces cerevisiae.
A microorganism. Alcohols and other solvents.
Zinc block
-
Metals.
78