AN SW E R S: CH EM I S T RY I N A C TI O N
ANSWERS
Unit 1a
Substances
Elements (i)
Everything in the world is made from about one hundred elements. Each one
has a name and a symbol that consists of one or two letters. The first letter
is always a capital letter (upper case) and the second letter is always lower
case (a small letter), e.g. the symbol for carbon is C but the symbol for
calcium is Ca. The symbol for some elements is based on the Latin name,
e.g. the symbol for potassium (kalium) is K and the symbol for sodium
(natrium) is Na.
Chemists have arranged elements
in the Periodic Table.
Most elements are solid at room temperature, e.g. carbon and copper. The
two elements that are liquid at room temperature are bromine and mercury.
Some elements are gases at room temperature, e.g. oxygen and hydrogen.*
Elements can be classified as metals and non-metals.
There are many more metals than non-metals.
The metals are found to the left side of the zig-zag line in the Periodic Table.
Some elements, including gold, silver and copper have been known for a
long time. The most recently discovered elements have been made by
scientists. These elements are found after uranium at the bottom of the
Periodic Table.
* (Many other examples of solids and gases are acce ptable.)
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Elements (ii)
Elements in the same group of the Periodic Table show
similar chemical properties, e.g.
sodium, lithium and
potassium are all stored under
oil because they are very
reactive.
.
Elements are used for many things.
Some examples of everyday uses of elements are shown in the table. *
Element
Use
Aluminium
Double-glazing frames, etc.
Chlorine
As a disinfectant in swimming pools.
Zinc
Battery cases, etc.
Carbon
As graphite in pencils, etc.
Iron
Nails, etc.
Argon
The gas in light bulbs, etc.
* (Other uses of the elements are acceptable. )
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Compounds and mixtures
A compound is a substance that is made up of two or more elements joined
together, e.g.

+
iron
sulphur
iron sulphide
Compounds with a name ending in ‘ -ide’ contain the two elements indicated,
e.g. the compound that contains calcium and oxygen is called
calcium oxide.
Similarly, sodium chloride contains
sodium and chlorine.
The name ending ‘-ite’ or ‘-ate’ indicates the additional element oxygen in
the compound, e.g. potassium sulphite and potassium sulphate both contain
potassium, sulphur and oxygen.
When two or more substances come together without reacting, a
mixture is formed. Air is a mixture of gases, approximately 80% nitrogen
and 20% oxygen.
The test for oxygen is that it relights a glowing splint.
A glowing splint does not relight in air because there is not enough oxygen.
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Solutions
A solution is formed when a substance dissolves in a liquid.

+
copper
sulphate
water
copper
sulphate
solution
A substance that dissolves in a liquid is soluble; a substance which does not
dissolve is insoluble.
A solution is diluted if more liquid is added to it.
A dilute solution has a lower concentration of dissolved substance than a
concentrated solution.
A saturated solution is one in which no more substance can be dissolved.
The gas which is dissolved in some drinks to make them fizzy is
carbon dioxide. The test for carbon dioxide is that it turns lime water milky.
The substance that dissolves in the liquid can be a solid, a liquid or a gas, e.g.
sugar is a solid that dissolves in water, alcohol is a liquid that dissolves in
water and sulphur dioxide is a gas that dissolves in water.
In some places, to kill bacteria, chlorine is
added to our drinking water. To prevent
tooth decay, sodium fluoride is added.
Compounds of lead, which can get into
drinking water from old pipes, can be
harmful to health.
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Hazards (i)
Regulations on the use of chemicals exist to ensure a safe working
environment for everyone who comes into contact with chemicals at work.
Simple hazard warning symbols, which can be easily recognised, are used to
identify the potential dangers of all chemicals.
Hazard symbols are on road tankers
to indicate dangers in the event of
accidents.
This shows that the chemical is toxic (a poison).
Taking or eating these chemicals would make you feel
very unwell and may even cause death.
This shows that the chemical is corrosive (sometimes
called caustic).
These chemicals can cause severe burns to the skin, as
well as holes in some metal objects.
This shows that the chemical is flammable (sometimes
called inflammable, which is the same thing).
Flammable chemicals catch fire and burn very easily.
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Hazards (ii)
This shows that the chemical is an irritant or harmful
chemical.
Chemicals with this warning symbol can make you
feel very unwell by affecting your skin or organs.
In many cases your lungs or breathing system can be
badly damaged by these chemicals.
This shows that the chemical is explosive.
As you might expect chemicals with this warning
symbol can explode!
This shows that the chemical is radioactive.
Exposure to radiation can be harmful and may lead to
cancer. This is why hospital staff in the
x-ray department will wear special (and very heavy)
clothes, or they will stand behind a protective screen.
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Unit 1b
Chemical reactions
Identification (i)
All chemical reactions involve the formation of one or more new substances.
Chemical reactions can be identified by changes in the appearance of
substances, including changes in colour.
Chemical reactions can also be identified by a gas being given off or a solid
(precipitate) forming on mixing two solutions.
Some examples of changes that can be observed during chemical reactions
are shown in the table.
Chemical reaction
Evidence of a reaction taking place
Making toast
It changes colour/goes black.
Magnesium with acid
A gas is evolved.
Iron rusting
A new substance is made.
Chemical reactions can also be identified by temperature changes that take place,
e.g. when an alkali reacts with an acid, nothing is seen but the test -tube becomes
hot because energy is produced, showing that a chemical reaction is taking place.
Identification (ii)
Some examples of the wide variety of chemical reactions that occur in the
world around us are shown in the table.*
Everyday chemical reactions
Frying an egg
A car rusting
Milk turning sour
Petrol burning
Toasting bread
A leaf rotting away
* (Other examples are acceptable. )
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Speed of reactions
The speed of a chemical reaction both in the laboratory and in our everyday life can
be affected by changes in particle size, temperature of reactants and concentration
of reactants.
Decreasing the particle size increases the speed of reaction; decreasing the
concentration decreases the speed of reaction; increasing the temperature increases
the speed of reaction.
A substance which speeds up a reaction but is not used up by the reaction is called
a catalyst. One example of an everyday use of a catalyst is shown in the table.
Catalyst
Everyday use
Transition metals in
catalytic converters
In car exhausts to convert harmful gases into
harmless gases.
Catalysts which affect reactions in living things are called enzymes.
They are used in everyday life.
Some examples of everyday uses of enzymes are shown in the table.*
Enzyme
Everyday use
Protease
In washing powders to help remove stains.
Zymase
To ferment sugars into alcohol.
Cellulase
To make jeans look more faded.
* (Other examples: Nickel for manufacturing margarine, Peroxides to make
plastics.)
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Word equations
In a chemical reaction, the starting substances are called the reactants and the
new substances that are formed are called the products.
A short-hand way of representing a chemical reaction is by a word
equation.
Consider, for example, the reaction of paraffin with oxygen to form water and
carbon dioxide.
The reactants are paraffin and oxygen.
The products are water and carbon dioxide.
The word equation for the reaction of sodium with water to form hydrogen
and sodium hydroxide is:
sodium + water

hydrogen + sodium hydroxide
Another word equation is:
ammonia + oxygen  nitrogen + water
This word equation describes the reaction between ammonia and oxygen to
form nitrogen and water.
In a word equation:
• the + (plus) sign means and
• the  (arrow) means changes into
• the reactants are always written to the left side of the arrow and the
products are always on the right side of the arrow.
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Unit 1c
Bonding
Molecules and ions (i)
Every element is made up of very small particl es called atoms.
An element is a substance that is made up of atoms of only one kind.
A silver ring contains millions of
atoms that are all the same.
iron
nail
silver
ring
Every atom in an iron nail is an atom of iron
and all atoms of iron are the same.
But an iron atom is different in size and mass from a silver atom.
Each element in the Periodic Table contains a different kind of atom. As well
as its own name, each element has its own number, called the atomic number.
The atomic number for potassium is 19 and the element with the atomic
number of 92 is called uranium.
When scientists make new elements, they make new kinds of atoms, i.e.
atoms with a different atomic number from all the rest.
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Molecules and ions (ii)
A molecule is a group of atoms (two or more) joined together.
The joins between the atoms are called bonds.
Some elements and compounds are made up of molecules.
strong bonds inside
the molecule
weak bonds between
the molecule
e.g. iodine is an element
made up of molecules
strong bonds inside
the molecule
weak bonds between
the molecule
and water (hydrogen oxide)
is a compound
made up of molecules.
The bonds inside the molecules are strong bonds.
The bonds between the molecules are weak bonds.
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Molecules and ions (iii)
Ions are atoms that have a charge.
There are two types of ion, one with a positive charge and the other with a
negative charge.
The bonds holding the oppositely charged ions together are strong.
Some compounds are made up of
ions, e.g. common
salt (sodium chloride).
The sodium ion (symbol Na + ) has a positive charge.
The chloride ion (symbol Cl – ) has a negative charge.
Substances like sodium chloride that are made up of ions are
called ionic compounds.
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Formulae – using models
The chemical formula indicates the number of atoms of each element in a
molecule of the substance, e.g. the chemical formu la O 2 shows that there are
two oxygen atoms in the molecule, the chemical formula CH 4 shows that
there is one carbon atom and four hydrogen atoms in the molecule.
One way of working out the chemical formula for a substance is by looking
at models or pictures of molecules.*
has the chemical formula C 2 H 6 O
has the chemical formula C 2 H 2 O 4
This compound
has the chemical formula CH 3 Cl
while
has the chemical formula C 2 H 4 O 2
* (Variations on the order of the elements in the formul ae are acceptable, e.g.
C 2 H 5 OH, C 2 OH 6 , etc.)
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Formulae – using prefixes
Some compounds have a prefix at the start of the name that enables us to
write the chemical formula directly from the name.
Prefix
Meaning
Name
Formula
Mono
1
Carbon monoxide
CO
Di
2
Carbon dioxide
CO 2
Tri
3
Sulphur trioxide
SO 3
Tetra
4
Silicon tetrachloride
SiCl 4
So
will have the chemical formula PH 3
phosphorus trihydride
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Unit 1d
Acids and alkalis
The pH scale
The pH scale is used to measure the acidity (or alkalinity) of a chemical.
The chemical must be dissolved in water, i.e. it must be a
solution for the pH to be measured.
The pH of a solution is usually measured using pH
paper or universal indicator.
The pH is found by comparing the colour of the
paper or indicator with a colour chart.
A pH meter can be used to find the pH of a solution
without the need to match with a colour chart.
The pH scale ranges from pH number 0 up to pH
number 14. Solutions that have a pH of below 7 are
acids; solutions that have a pH above 7 are alkalis.
The pH of water and neutral solutions is 7.
The lower the pH of an acid, the greater the acidity;
a solution with a pH of 2 is more acid than a solution
with a pH of 6.
The higher the pH of an alkali, the greater the alkalinity; a solution with a pH
of 14 is more alkaline than a solution with a pH of 10.
Solutions are diluted by the addition of water.
As an acid solution is diluted, the acidity of the solution decreases and the
pH increases. As an alkaline solution is diluted, the alkalinity of the solution
decreases and the pH decreases.
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Common acids and alkalis
hydrochloric
acid
sodium hydroxide
lemonade
oven cleaner
solution
Acids and alkalis are used in the home, in industry and in school.
Common laboratory acids include hydrochloric acid, sulphuric acid and
nitric acid.
Common laboratory alkalis include sodium hydroxide solution, lime water
and ammonia solution.
Common household acids include vinegar, lemonade and soda water.
Common household alkalis include baking soda, oven cleaner, dishwashing
powder, bleach and soaps.
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Neutralisation (i)
Acids have a pH of less than 7; alkalis have a pH of
more than 7. When an alkali is added to an acid, the reaction that takes place
raises the pH of the acid.
When an acid is added to an alkali, the reaction that takes place lowers the
pH of the alkali.
When an acid reacts with an alkali the pH of both solutions moves towards 7.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Since a solution with a pH of 7 is neutral, the type of reaction which takes
place is called neutralisation. A neutral solution is produced because the
acid and the alkali react to form water. The other product of the reaction is
called a salt.
The general word equation for an acid/alkali reaction is:
an acid
+ an alkali

a salt + water
The name of the salt comes from the acid and the alkali.
The first part of the name comes from the metal of the alkali,
e.g. sodium hydroxide forms sodium salts and potassium hydroxide forms
potassium salts.
The second part of the name comes from the acid, as shown in the table
below.
Name of acid
Name of salt formed
Hydrochloric
A type of chloride
Sulphuric
A type of sulphate
Nitric
A type of nitrate
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Neutralisation (ii)
The names of some salts formed in acid/alkali reactions are shown in the
table below.
Name of alkali
Name of acid
Name of salt formed
Sodium hydroxide
Hydrochloric
Sodium chloride
Lithium hydroxide
Nitric
Lithium nitrate
Potassium hydroxide
Sulphuric
Potassium sulphate
So the word equation for the reaction of sodium hydroxide with sulphuric
acid is:
Sodium hydroxide + sulphuric acid


Sodium sulphate + water
Carbon dioxide gas is produced in the
reaction of an acid with a metal
carbonate.
The gas can be identified because it turns
lime water
milky. The other two products of this
acid
metal carbonate
type of reaction are a salt
and water.
Since water is formed in the reaction of an acid with a metal carbonat e,
the type of reaction is again called neutralisation.
The general word equation for an acid/metal carbonate reaction is:
acid + metal carbonate

a salt + water + carbon dioxide
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So the word equation for the reaction of iron carbonate with hydrochloric
acid is:
iron carbonate + hydrochloric acid
 

iron chloride + water + carbon dioxide
Copper sulphate can be made by the reaction
of copper carbonate with
sulphuric acid.
The unreacted solid copper carbonate can be
removed from the solution by
filtering.
excess
copper
carbonate
copper
sulphate
solution
evaporating
basin
A solid sample of the salt can be obtained
by heating the solution with a bunsen
burner to evaporate the water.
tripod
gentle heat
Treatment of acid indigestion is an everyday example of neutralisation. The
indigestion tablet contains a chemical that increases the pH of the acid in the
stomach. Other everyday examples of neutralisation involve the use of
chemicals to reduce the pH of the soil and lakes.
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Acid rain
When carbon and sulphur burn, they react with oxygen to form gases. Carbon
reacts to form carbon dioxide; sulphur reacts to form sulphur dioxide, a gas
with a very unpleasant smell.
Although nitrogen does not burn in the same way as carbon and sulphur, the
gas does react with oxygen to form the brown gas called nitrogen dioxide.
Carbon, sulphur and nitrogen are all non-metal elements.
The gases produced all dissolve in water to form acidic solutions.
Sulphur dioxide is
produced in the air when
the sulphur
that is found in some
fossil fuels also burns.
The sparking of air in car
engines forms nitrogen
dioxide. Sulphur dioxide and
nitrogen dioxide dissolve in
water in the atmosphere to
produce acid rain.
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Acid rain is destroying trees.
Acid rain has increased the acidity of water in rivers and lochs.
Some examples of the damaging effect of acid rain on structures made of
carbonate rock and iron or steel, soils, and plant and animal life are shown in
the table below.
Effect on:
Damaging effect
Carbonate rock
Reacts with acid rain and dissolves.
Iron and steel
Rusts very fast and becomes weakened.
Soil
Becomes acidic. Aluminium leached out.
Plant life
Can die if soil is too acidic.
Animal life
Pond/lake animals die if water too acidic.
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UNIT 2
Unit 2a
Metals
Uses (i)
Metallic elements are to the left side of the zig-zag line in the Periodic Table.
A few metals, including gold, silver and copper, are found in the Earth’s
crust.
Most metals are found combined with other elements.
Most metals have to be extracted from their ores before they can be used.
Some metals, including iron, are extracted from their ores by heating with
carbon. Iron is extracted from its ore in a blast furnace. Some metals,
including aluminium, are extracted from their ores using electricity.
All metal elements are conductors of electricity.
Elements that are non-metals do not conduct electricity; carbon in the form
of graphite is an exception.
The use that we make of a metal depends on its specific properties.
Property
What it means
Thermal conductivity
How well a metal conducts heat
Electrical conductivity
How well a metal conducts electricity
Strength
How strong a metal is
Density
How heavy a certain volume of metal is
Maleability
How easily a metal can be shaped
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Uses (ii)
Some examples of how the …………………… of metals are related to their
properties are shown in the table below.
Metal
Use
Property
Iron
Vehicle parts
High strength
Aluminium
Aircraft parts
Low density
Copper
Electrical wiring
Good electrical
conductor
An alloy is a mixture of metals. Brass, solder and stainless steel are
examples of alloys.
Some examples of the uses of alloys are shown in the table below.*
Alloy
Use
Cupro-nickel
To make coins.
Solder
To join electrical connections.
‘Stainless’ steel
To make cutlery.
* (Other metals and uses/properties are acceptable – these possibilities refer
to the pictures given. )
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Reactions (i)
Metals take part in some important chemical reactions.
Metal oxides are produced in the reactions of metals with oxygen, e.g.
magnesium reacts with oxygen to form magnesium oxide.
Lithium, sodium and potassium are all kept under oil to protect them from
the atmosphere.
These metals react slowly with the oxygen of the air.
metal
safety screen
However, these metals react
violently with water.
The speed of the reaction of calcium metal
with water is suitable for the collection of the gas produced.
The gas produced when a metal reacts with water is called
hydrogen gas.
The test for hydrogen is that it burns with a pop.
Metals that react with acids also produce hydrogen gas.
A salt that takes its name from the metal and the acid is also formed, e.g. zinc
reacts with hydrochloric acid to produce
zinc chloride and hydrogen, magnesium reacts with sulphuric acid to
produce magnesium sulphate and hydrogen.
Some metals, including copper, silver and gold, do not react with dilute acid.
Differences in the reactions of metals with oxygen, water and acid give an
indication of the reactivity of the metals. This is shown on page 6 of the data
booklet.
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water
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Reactions* (ii)
Iron is less reactive than aluminium;
zinc is more reactive than copper.
An example of a metal that reacts with oxygen is magnesium;
an example of a metal that does not react with oxygen is gold.
An example of a metal that reacts with water is sodium;
an example of a metal that does not react with water is copper.
An example of a metal that reacts with acid is magnesium;
an example of a metal that does not react with acid is copper.
* (Other examples of metals reacting – or not reacting – with oxygen, water
and acids are possible. )
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Corrosion (i)
When some metals are left in the open air, they tend to break up at the
surface. The metal object gradually disappears as the oxide layer flakes off.
This process is called corrosion and in the special case of iron it is called
rusting. Rusting results in the iron losing its strength.
Iron does not rust in a test
tube of dry air showing
that water
is required for rusting
to take place.
Iron does not rust in water
that has been boiled showing
that oxygen (from the air) is
stopper
cotton
wool
oil film
drying
agent
boiled
water
required for rusting.
Iron rusts in moist air because both water and oxygen are present.
When iron rusts, the surface of the metal changes from an element to a
compound. The iron atoms in the element react to form iron ions in the
compound. A rust indicator can be used to detect iron ions and hence
measure the amount of rusting that takes place. The more blue colour, the
more rusting there is.
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moist
air
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Corrosion (ii)
tap water
+
rust indicator
acid rain
+
rust indicator
salt water
+
rust indicator
In the above experiment, there is more blue colour around the nail in the acid
rain than the nail in the tap water. This shows that iron rusts quicker in acid
rain. Because of the higher levels of acid rain, cars in city areas usually rust
quicker than cars in country areas.
There is more blue colour around the nail in the salt water than around the
nail in the tap water. This shows that iron rusts quicker in salt water.
Putting winter salt on the roads increases the speed of rusting of a car. Also,
car owners who live near the sea should wash their cars mor e than owners
who live inland to remove the salt.
Iron can be protected from rusting by making a surface barrier that prevents
water and oxygen from coming into contact with the iron. There are several
relatively inexpensive ways of doing this, e.g. painting, greasing and coating
with plastic.
When iron is galvanised, it is dipped into molten zinc to coat the iron with
that metal, e.g. for dustbins.
In electroplating, electricity is used to cover iron with a thin layer of a new
metal, e.g. chrome on bicycles.
Cans containing food are tin-plated to prevent corrosion.
Iron can also be protected by attaching the iron to certain other metals. This
method of protection is very different from providing a surface barrier.
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Corrosion (iii)
iron nail in
magnesium
zinc attached
tin attached
rust indicator
attached to
iron nail
to iron nail
to iron nail
There is no blue colour around the nails attached to magnesium and zinc
showing that the nails are not rusting. The metals that protect iron in this
way are all more reactive than the iron itself.
Since zinc is more reactive than iron, galvanising (coating iron with zinc)
provides this kind of protection as well as providing a surface barrier.
Bags of scrap magnesium (a more reactive metal than iron) are attached to
underground iron and steel pipes to protect the iron in this way.
Aluminium is a more reactive metal than iron and yet it does not appear to
corrode. Aluminium tends to be slow to react because it is usually covered
by a thin layer of aluminium oxide. The process of using electricity to
increase the thickness of the oxide layer, providing increased protection
against corrosion, is called anodising.
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Batteries
When a battery is in use the chemicals in
the battery react to make electricity.
Chemical energy is changed to electrical
energy.
When all the chemicals are used up by the
chemical reaction, the battery can no
longer make electricity, i.e. the battery is ‘dead’
and it has to be replaced.
Batteries that can be recharged are able to be used over and over again, e.g.
the lead-acid battery that is used in cars and the nickel-cadmium battery.
Electricity can be produced by connecting two different metals together to
make a cell.
voltmeter
metal 2
filter paper soaked in ion
solution
magnesium
A solution containing ions is needed to complete the circuit between the
metals. The voltage is related to the difference in the reactivity of the metals.
Magnesium joined to silver will produce a larger voltage than magnesium
joined to copper.
Zinc joined to iron will produce a lower voltage than zinc joined to tin.
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Unit 2b
Personal needs
Keeping clean
When cleaning hair, skin and clothes, it is difficult to remove oil and grease
by washing with water.
They are difficult to remove because they are insoluble in water. Cleaning
chemicals enable oil and grease to mix with the water. These chemicals
break up the oil and grease into tiny droplets.
This happens because the cleaning chemicals are soluble in both oil and
grease and water.
oil
water
oil droplets in water
Examples of manufactured products that contain cleaning chemicals include
soaps, detergents, shampoos and washing-up liquids and powders.
Hard water contains certain dissolved compounds that are not found in soft
water. Soaps that form a lather in soft water can form a scum with hard
water.
As a result, soapless detergents are used to produce a lather with hard water.
Dry cleaning uses special solvents that are particularly
good at dissolving oil and grease stains.
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Clothing
Clothing fabrics are made from thin strands called fibres.
Fibres are made up of long-chain molecules called polymers. Fibres can be
classified as natural (made from plants or animals) or synthetic (made by the
chemical industry).
Examples of natural fibres include silk, wool and cotton.
woollen jumper
Examples of synthetic fibres include nylon and polyesters, e.g. Terylene.
Terylene trousers
Fibres that are synthetic can be designed to have the specific properties
needed for a particular use.
Dyes are coloured compounds that are used to produce brigh tly coloured
fabrics. Most dyes require the use of a compound to ‘fix’ the dye to the
fabric and make the colour permanent.
Sometimes fabrics can be treated with chemicals to improve their properties,
e.g. flame proofing a fabric for children’s clothes.
Fibres that form strong bonds with water molecules are hard to drip-dry but
they do not feel ‘sweaty’ to wear because they soak -up perspiration.
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Unit 2c
Fuels
Fire (i)
A fuel is a chemical that is burned to produce energy. When a substance
burns it reacts with oxygen.
Combustion is another word for burning.
As well as a fuel, a fire needs oxygen (usually from the air) and a
temperature high enough to start the fire and keep it going. This is shown in
the fire triangle.
Perhaps the most frequent way to fight a fire is to pour water on to the flames
of the fire, e.g. a bonfire. However, water must not be used with oil, petrol
and electrical fires.
A fire blanket can be put over the flames or carbon dioxide gas or foam from
a cylinder can be used both in the lab and at home, e.g. for a chip -pan fire.
In the lab there will also be a bucket of sand for fighting fires.
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Fire (ii)
Fire-fighting methods try to remove any one of what is at the three sides of
the fire triangle. When this happens the fire goes out.
Fire-fighting method
What is removed
Covering burning oil with a towel
Oxygen
Spraying water on a bonfire
Heat
Controlled burning of trees in the path of a
Fuel
forest fire
Spraying carbon dioxide on a burning car
Oxygen
Pouring sand on burning magnesium
Oxygen
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Finite resources (i)
Most of the fuels that we use today are made from the remains of plants and
animals. Over many millions of years, the pressures and temperatures under
the ground change the remains to produce the fuels. The fuels formed in this
way are known as fossil fuels.
Examples of fossil fuels include coal, oil, natural gas and peat.
Fossil fuels are a finite resource, i.e. they cannot be replaced when they have
been used. Over-use of fossil fuels could lead to a fuel crisis, i.e. there could
be a shortage of fuels or the supply could even run out. To conserve our
supplies of fossil fuels, energy should be saved whenever possible, e.g. by
turning out lights and not overheating rooms.
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Finite resources (ii)
Fossil fuels have to be transported by oil tankers around the world to where
they are most needed. This can lead to oil spillages at sea. When this
happens serious damage can be caused to marine life, e.g. oil o n the feathers
of birds, and to the sea-side environment in general, e.g. oil on sandy
beaches.
The chemical compounds found in fossil fuels are mainly hydrocarbons. A
hydrocarbon is a compound that contains hydrogen and carbon only, e.g.
butane, C 4 H 10 , is a hydrocarbon but acetone, C 2 H 6 O, is not.
When a hydrocarbon burns in a plentiful supply of air, the hydrogen and
carbon atoms in the compound both react with oxygen. The two products of
the reaction are carbon dioxide and water.
Carbon dioxide can be identified because it turns lime water milky while
water can be identified by its boiling point of 100°C.
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Renewable resources
New fuels that are renewable sources of energy, i.e. able to be replaced, can
be used instead of fossil fuels.
Biogas can be generated by the decomposition of waste plant material. The
main renewable source of energy in biogas is methane.
The renewable source of energy that can be obtained from sugar cane
is ethanol. This can be mixed with petrol to make a fuel
for cars.
Hydrogen, a renewable source of energy obtained from water, is a likely fuel
for the future.
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Important processes (i)
A mixture of liquids can be separated by using the difference in boiling
points, e.g. alcohol and water are separated in the manufacture of whisky in a
distillery.
This type of separation process is called distillation.
Distillation of liquid air is used in industry to separate oxygen and nitrogen.
The process of distillation involves heating a liquid until it boils to form
a gas and then cooling the gas somewhere else to make it condense into a
liquid.
The boiling point is related to the mass of the molecules in the liquid.
bottled gas & chemicals
4 carbon atoms
Crude oil is a mixture of chemical
compounds, mainly hydrocarbons.
Before it can be used, the many
petrol, chemicals & solvents
5 to 10 carbon atoms
different liquids and dissolved
solids and gases in it have to be
separated into fractions that
contain compounds of roughly the
same boiling point.
This process is called
fractional distillation.
The largest molecules are found
in the fraction with the highest
boiling point; the smallest
molecules found in the fraction
with the lowest boiling point.
kerosene & paraffin
10 to 16 carbon atoms
diesel and heating oil
14 to 20 carbon atoms
crude
oil in
lubricating oil & greases
20+ carbon atoms
heater
bitumen residue
The fractional distillation of crude oil produces many useful fuels.
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Important processes (ii)
A use for each of the fractions is shown in the table below.
Name of fraction
Use
Gas
Bottled gas for heating/cooking.
Petrol
Fuel for cars.
Diesel
Fuel for trains, lorries, cars.
Kerosene
Fuel for jet aircraft.
Lubricating oil
For engines.
Bitumen
For roads and roofing.
The process of fractional distillation can be simulated in the laboratory.
The uses of the fractions are related to the boiling point ranges, ease of
evaporation, flammability and viscosity (thickness) of the fractions.
Gas
Petrol
Diesel
Kerosene
(Paraffin)
Lubricating
oil
Bitumen
-------- Lighter / darker in colour -------------------------------------------->
--------- Increase / decrease in boiling point ----------------------------->
--------- Increase / decrease in ease of evaporation ------------------>
---------- Increase / decrease in viscosity ----------------------------------->
---------- Increase / decrease in molecular size ------------------------->
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Important processes (iii)
Fractional distillation produces more molecules that are large in size than are
needed that for present-day industrial purposes.
Fuel gas
Petrol
Naphtha Kerosene
Diesel
Fuel oil
oil
and bitumen
Name of fractions
These less popular molecules can be broken up to produce more of the
smaller molecules that are more useful.
This process is called cracking.
The cracking of the hydrocarbon with the chemical formula C 12 H 26 can
produce the hydrocarbon products shown in the table below.
Reaction
Reactant
Formulae of molecules produced
1
C 12 H 26
C 10 H 22 + C 2 H 4
2
C 12 H 26
C 8 H 16 + C 4 H 10
3
C 12 H 26
C 5 H 12 + C 2 H 4 + C 5 H 10
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Pollution problems (i)
Air pollution is a result of impurities in the air. Most of these pollutants
come from the burning of hydrocarbon fuels such as oil and petrol. Air
pollution is therefore more of a problem in industrial areas.
When a hydrocarbon fuel burns in a good supply of oxygen, the carbon reacts
with oxygen in the air to form carbon dioxide.
When there is a poor oxygen supply, e.g. in a car engine,
carbon monoxide is also produced. Carbon monoxide is dangerous because it
is a poisonous gas. This gas reacts with haemoglobin in the blood, stopping
it carrying oxygen to the brain and other parts of the body. In Tokyo, traffic
police wear face masks at the rush-hours to protect them from carbon
monoxide pollution.
Carbon is also a product of burning hydrocarbons in a poor supply of oxygen
and soot particles produced by the burning of diesel are also potentially
harmful.
Compounds of lead that are added to petrol cause pollution. In this country
nearly all cars run on unleaded petrol. However, different hydrocarbons are
used to make unleaded petrol and the benzene fumes in unleaded petrol are
toxic.
Since crude oil contains small amounts of sulphur, the burning of fuels
obtained from crude oil produces sulphur dioxide. This gas dissolves in rain
water to form acid rain, which attacks iron and the stonework of buildings as
well as plants and trees. To reduce air pollution sulphur compounds can be
removed from petrol and used to manufacture sulphuric acid.
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Pollution problems (ii)
Nitrogen and oxygen in the air do not normally react but the spark that ignites
the petrol can provide the energy to produce a reaction. As a result, oxides of
nitrogen, which are also poisonous gases, are found in car exhaust fumes as
well.
Special exhaust systems with catalytic converters speed
up the conversion of pollutant gases to harmless gases. These systems
contain transition metals (metals in the rows in the middle of the Periodic
Table), which act as catalysts for these reactions.
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Unit 2d
Plastics
Uses
Plastics are not natural materials like wood and stone.
They are synthetic materials, i.e. made by the chemical industry.
Most plastics are made from crude oil.
Examples of plastics include polythene, polystyrene,
perspex, nylon, kevlar, silicones, bakelite and formica.
The everyday uses of plastics are related to their properties.
Plastic
Property
Use
Polythene*
Strong
Carrier bags
Perspex
Transparent
Substitute for glass
Silicone
Waterproof
Frame sealants
* (Other polymers are possible, e.g. kevlar is tough and used to make mountain
bike tyres/bulletproof vests; and PVC is waterproof and used to make garden
hoses/window frames.)
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Advantages and disadvantages (i)
Many natural and synthetic materials are used for the same purpose.
Materials like wood, glass, metals and paper can now be replaced by plastics.
Some advantages of natural materials and plastics are shown in the tables.
Natural material
Use
Advantage
Wood
Floors/joists
Strong
Cotton
T-shirts etc.
Cool in hot weather
Slate
Roofing tiles
Long lasting
Plastics
Uses
Advantage
Formica
Kitchen worktops
Heat resistant
scratch resistant
PVC
Drainpipes and
Maintenance free
replacement windows
Expanded polystyrene
Packaging
Light
Plastics are quite cheap, light and can be easily moulded into different shapes.
However, the durability and lightness of plastics can cause problems.
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Advantages and disadvantages (ii)
The leaves from the trees are biodegradable, i.e. able to be broken down by
bacteria and weather. ‘Bio’ refers to living things and degradable means
‘able to rot away’.
Since plastics are not
biodegradable this leads to an
unsightly environment that
can be dangerous to animals.
To help with the disposal of plastic
waste, chemists are investigating
the development of
biodegradable plastics.
plastic litter is unsightly
Further problems can arise with the burning of plastics, e.g. fires involving
plastics are extremely dangerous.
Carbon monoxide, a poisonous gas can
be given off from just about any burning plastic.
Other gases produced depend on the elements
in the plastic, e.g. PVC contains chlorine and
so burning PVC can produce hydrogen
chloride.
Options for the disposal of plastics include incineration, recycling and
burying. With incineration, the heat generated can be used as a source of
energy but there are problems with emissions.
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Since plastics are made from
crude oil, which is a
finite resource, recycling
is to be encouraged and special
containers are available in
many places for this purpose.
However, recycling can be
difficult because of
the many different kinds of
plastic waste
plastics in common use.
To conserve oil supplies, chemists are looking for ways of making plastics
from renewable sources.
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Thermoplastics/thermosetting plastics (i)
Plastics can be classified according to what happens to them when
they are heated.
Plastics that soften on heating
are known as thermoplastics
(thermosoftening plastics).
This enables them to be
reshaped over and over
again.
Examples of thermoplastics
include nylon and polythene.*
thermoplastics
Plastics that harden on heating are
known as thermosetting plastics.
They cannot be reshaped because
they do not melt on reheating.
Examples of thermosetting plastics
include urea formaldehyde and
melamine formaldehyde.
thermosetting plastics
The uses of thermosetting plastics depend on their two main properties, i.e.
they do not soften on heating and they do not conduct electricity. Electrical
plugs and sockets and kitchen worktops are made from thermosetting
plastics.
* (Other examples of thermoplastics are acceptable, e.g. polyesters.)
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Thermoplastic/thermosetting plastics (ii)
Plastics are made of very long molecules containing hundreds of carbon
atoms linked together to make a chain.
The large molecule is called a polymer.
Polymers are made by the joining together of small molecules. The small
molecule is called a monomer.
The process of making a polymer from monomer units is called
polymerisation.
The names of polymers are related to the names of the monomers from which
they are made, as shown in the table below.
Name of monomer
Name of polymer
Ethene
Poly(ethene)
Styrene
Polystyrene
Propene
Poly(propene)
Chloroethene
Poly(chloroethene)
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UNIT 3
Unit 3a
Photosynthesis and respiration
Photosynthesis
Plants make their own food by taking in substances from the environment.
This process is called photosynthesis.
Plants use carbon dioxide from the air to make glucose.
This gas is absorbed through the leaves of plants.
The other reactant is water, which is taken in from the soil through the roots of
plants.
As well as glucose, a gas which relights a glowing splint is also formed. This
is oxygen and it is released into the air through the leaves of the plants.
The ‘photo’ part of photosynthesis indicates that light energy is required for
the process to take place. The chlorophyll in the leaves absorbs the light
energy required for photosynthesis. Chlorophyll is the che mical that gives
plants their green colour.
The word equation for the photosynthesis reaction is:
carbon dioxide + water  glucose + oxygen
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Respiration
Animals can obtain energy by a process called respiration.
The reactants are glucose and oxygen.
Animals obtain glucose by eating food that has come from plants.
When exhaled air is blown into lime water, the lime water turns
milky. This shows that carbon dioxide is one of the products of respiration.
Also produced in respiration is water.
The energy produced in the process is used in a wide variety of ways,
e.g. for warmth and movement.
The word equation for the respiration reaction is:
glucose + oxygen  carbon dioxide + water.
Respiration is the reverse of photosynthesis.
The processes of photosynthesis and respiration maintain constant amounts of
oxygen and carbon dioxide in the air. The oxygen used up in respiration is
produced by photosynthesis; the carbon dioxide produced by respiration is
used up by photosynthesis.
energy
out
respiration
glucose
oxygen
carbon dioxide
water
photosynthesis
energy
in
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The greenhouse effect (i)
Carbon dioxide in the atmosphere is one of the main causes of the greenhouse
effect. The greenhouse effect is important because it prevents tempera tures on
the Earth becoming too cold for normal life to exist.
Sun
carbon dioxide layer
Earth
Carbon dioxide is removed from the atmosphere by the process known as
photosynthesis. Extensive clearing of forests reduces the amount of carbon
dioxide removed in this way.
The combustion of fossil fuels produces carbon dioxide. Increased levels of
carbon dioxide in the atmosphere may also be due to an increase in the
combustion of such fuels.
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The greenhouse effect (ii)
Sun
carbon dioxide layer
Earth
An increase in the level of carbon dioxide in the atmosphere could cause the
atmosphere to retain more of the Sun’s energy as heat. This process is known
as global warming.
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Unit 3b
The effect of chemicals on the growth of plants
Using chemicals to save plants
Farmers and gardeners use chemicals to try to ensure a good crop yield.
Pesticides are used to control
pests; pests eat the crops.
Fungicides are used to prevent
diseases that are caused by
bacteria and fungi; diseases lead to
poor growth of plants.
Herbicides are used to kill weeds;
weeds can inhibit the growth of plants
by using up essential chemicals in the soil.
fungicide
herbicide
pesticide
Pesticides, fungicides and herbicides are toxic and so must be used with great
care.
Natural predators (animals that eat other animals) can also be used to safely
control pests, e.g. birds in the garden eat a wide variety of insects.
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Fertilisers (i)
Nitrogen (symbol N), phosphorus (P) and potassium (K) are essential elements
for healthy plant growth.
These elements are taken in from
the soil through the roots
of plants.
The elements are taken in as
compounds and not as the
soil
free elements.
To be taken in by plants, the
compounds are dissolved in
water, i.e. in solution.
nitrogen
compounds
phosphorus
compounds
potassium
compounds
In areas of natural vegetation, e.g. woodland, the decay of plant and animal
remains returns all essential elements to the soil.
However, where crops are harvested and the essential elements removed,
fertilisers must be added to the soil to restore the elements required f or healthy
growth of plants. Fertilisers are known as NPK compounds as they contain
nitrogen, phosphorus, and potassium.
Natural fertilisers are produced by the natural breakdown of plant and animal
remains. Examples of natural fertilisers are compost and manure. Fertilisers
that are made by the chemical industry are said to be artificial.
The increase in the demand for food production has resulted in greater use of
artificial fertilisers. The major artificial fertilisers are potassium, nitrate,
phosphate and potassium compounds.
Type of compound
Essential element in it
Ammonium
Nitrogen
Nitrate
Nitrogen
Potassium
Potassium
Phosphate
Phosphorus
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Fertilisers (ii)
Potassium nitrate can be made by the reaction of an acid with an alkali.
The word equation for the reaction is:
nitric acid + potassium hydroxide

potassium nitrate + water
To be effective, the compounds in
fertilisers must be soluble in
water.
However, the extensive use of
artificial fertilisers has increased
the levels of nitrate compounds in
some rivers and lochs.
The presence of large quantities of
nitrate compounds can leave the
water lifeless.
Some plants have root nodules in
which nitrogen from the air is
converted into nitrates. These
compounds include clover, beans
and peas.
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Unit 3c
Food and diet
Elements in the body
A variety of different foods
are needed to supply the
different chemical elements
and compounds required
by the body.
A balanced diet has a good
mix of the different types of food
and is therefore a healthy
diet.
Essential compounds include
carbohydrates, fats and proteins.
More than 60% of body weight is made up of water.
The main elements in the compounds in the body are
oxygen, carbon, hydrogen and nitrogen. These elements are present in the
body as compounds and not as free elements.
Minerals supply the body with calcium, which is
required for strong bones and teeth, and
iron, which is important for healthy blood.
Elements that are only needed in very minute quantiti es are called trace
elements. These elements are also supplied by minerals.
Some trace elements if taken in too large quantities are toxic, i.e. they act as a
poison.
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Different carbohydrates
Carbohydrates form an important class
of food made by plants.
Carbohydrates are needed by the body
to provide energy.
Foods rich in carbohydrates include
bread, rice and potatoes.*
Carbohydrates are compounds that
contain the elements carbon, hydrogen and oxygen.
Carbohydrates can be divided into sugars and starches.
Examples of sugars include sucrose (table sugar), glucose, fructose and
maltose.
Most sugars can be detected by Benedict’s solution.
The sugar that is an exception is sucrose. When the result of a test for a sugar
is positive, the solution, on heating, turns from a blue colour to an orange-red
colour.
Iodine solution is used to test for starch. When the result of a test for starch is
positive the solution turns from a wine -red colour to a blue-black colour.
Sugars have a sweet taste and are very soluble in water.
Starch does not have a sweet taste and does not dissolve in water.
* (Other examples of carbohydrates are acceptable. )
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Reactions of carbohydrates
Sugars dissolve in water; they are made up of molecules that a re small in size.
Starch does not dissolve in water; starch is made up of very long chain
molecules.
Very long-chain molecules, like starch, are examples of polymers.
The small molecules that join together to make starch are examples
of monomers.
Starch is made by the joining together of molecules of glucose.
Plants convert the glucose into starch for storing energy.
During the digestion of starchy foods, the starch is broken down into glucose.
Glucose is transported round the body in the blood(stream). Body cells pick
up the glucose and use it for the process called respiration.
Starch is broken down in the body by enzymes (biological catalysts).
Body enzymes work best at body temperature ( 37°C).
At higher temperatures, body enzymes are destroyed.
In the lab, starch can be broken down by acid as well as by enzymes.
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Fats and oils
Fats and oils form an important class of
food obtained from both plants and
animals.
Fats and oils are much more concentrated
sources of energy than carbohydrates.
Fats and oils can be detected by a special test using filter paper. The fat or oil
leaves a grease stain on the paper.
Saturates are compounds that are made up of
molecules that are said to be
saturated; unsaturates are
compounds that are made up of molecules
that are said to be unsaturated.
Compounds that are made up of long chain
molecules (polymers) that are said
to be unsaturated are known as polyunsaturates.
Saturates are believed to increase the cholesterol level in the bloodstream.
Medical opinion suggests that total fat consumption should be reduced and,
where possible, foods with polyunsaturates should be eaten. Foods containing
polyunsaturates are considered less likely to cause heart disease.
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Proteins
Proteins form an important class of food
obtained from both plants and
animals.
Foods rich in proteins include
meat and cheese.*
Proteins provide material for body
growth and repair, e.g. growth of hair and nails.*
Proteins can be detected by heating with soda lime and testing for an alkaline
gas, i.e. a gas that turns pH paper a blue colour.
Proteins are chemical compounds made up of the elements carbon, hydrogen,
oxygen and nitrogen.
Very large long-chain molecules, like proteins, are examples of polymers. The
small molecules that join together to make proteins are examples of monomers.
The monomer molecules that join together
to make proteins are amino acid
molecules.
The process of making proteins from amino
acids is called polymerisation.
During digestion, proteins in foods
are broken down to amino acids.
The amino acids required to make animal proteins can be obtained from foods
that come from both animal and vegetables. A vegetarian diet must include a
wide variety of foods to supply all the necessary amino acids. The amino acids
are then used by animals to make proteins for specific purposes, e.g. human
hair, wool on sheep.
* (Other examples of protein foods are acceptable, as are other examples of
protein materials, e.g. skin, musc le.)
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Fibres, vitamins and food additives
Fibre is an essential part of a
balanced diet.
Foods rich in fibre include
cereals and vegetables.
Fibre absorbs water and
swells up.
The swollen fibre provides bulk for the
muscles to work on as food is squeezed along the gut.
This keeps the gut working well and helps to prevent constipation.
Vitamins are a collection of complex compounds all containing the element
carbon. They are needed to keep the body healthy.
Food additives are added to foods for a variety of reasons.
Vitamins and minerals are added to enhance the nutritional value of food.
Food preservatives enable
food to be kept for
longer.
Food colourings are used to
improve the appearance
of food.
Food flavourings add to the flavour of food.
Food additives can be used only if they have been tested and approved.
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Unit 3d
Drugs
Alcohol (i)
A drug is a substance that alters the way the body works.
Alcohol is a drug; if taken in excess, alcohol can have harmful effects on
health and affect lifestyle.
In the body, alcohol can cause particular damage to the liver and a transplant
may be needed in extreme cases. Alcohol can also affect the brain, e.g. the
time for a driver of a car to react is longer after drinking alcohol.
The level of alcohol in alcoholic drinks can be stated in units.
A bottle of alcopop or a pint of beer
contains approximately
2 units of alcohol.
A pub measure of spirit or a glass of
wine contain approximately
1 unit of alcohol.
Alcohol is broken down by the body at
about 1 unit per hour.
Alcohol for alcoholic drinks can be made from starch and sugars present in
fruit and vegetables. The type of alcoholic drink varies with the plant source
of the carbohydrate.
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Alcohol (ii)
The production of alcoholic drinks from carbohydrates occurs by a process
called fermentation. The carbohydrate that reacts is glucose. Yeast provides
the enzymes that act as a catalyst for the reaction. The alcohol produced by
fermentation is called ethanol.
During fermentation, carbon dioxide gas is also produced.
The word equation for the reaction is:
glucose  ethanol + carbon dioxide
Water and alcohol can be partially separated because they have different
boiling points. This process is called distillation.
It is a method of increasing the alcohol concentration of alcoholic drinks .
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Other drugs
Some drugs are legal, other drugs are illegal.
Drug
Legal or illegal
Alcohol
Legal
Caffeine
Legal
Cannabis
Illegal
Ecstasy
Illegal
Nicotine
Legal
LSD
Illegal
Being unable to manage without a drug is known as
addiction.
Methanol, another alcohol, is very toxic.
Drinking methanol can cause blindness and even
death.
Methylated spirits (meths) contains methanol.
It has both a colour and a bad tasting substance
added to it to deter people from drinking it.
The drugs that doctors use to try to cure illnesses are found in medicines.
These drugs help to maintain the important chemical reactions that are going
on all the time in our bodies. Diseases and infections can be caused by microorganisms interfering with these chemical reactions.
Some drugs, including antibiotics, can fight the
micro-organisms. Medicines may be made of several
chemicals but only the active ingredients work
on the body.
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