Bubbling Chemistry 1.0eng
Heureka, The Finnish Science Centre, www.heureka.fi
Kati Tyystjärvi kati.tyystjarvi@heureka.fi
1. General
Bubbling chemistry is generally the first laboratory activity for elementary school
groups. The purpose of the activity is to provide even the youngest of students the
opportunity to try laboratory experimentation using the correct tools and materials, as
well as to provide their first exposure to the field of chemical research by learning
about substances and their properties and reactions.
2. Chemistry and the chemist
Chemistry is a natural science, which studies substances and their properties and
structures. Substances are comprised of elements, of which there are a total of 109
including synthetic elements.
An element is a substance whose atoms all have the same nuclear charge and atomic
number (periodic table). Elements cannot be separated chemically into simpler
substances. Each element has a chemical symbol, which is generally derived from its
Latin name. The names of the elements have their own histories: the names are often
based on a property of the element or are named after famous chemists or their
domiciles.
Chemists work in the fields of food manufacturing, cosmetics and explosives, as well
as in pharmaceutical plants, metal works, hospitals and criminal investigation
laboratories, to name a few. A chemist may also be an inventor who invents new
compounds.
3. The states of matter
The state of matter changes when the temperature changes. The transition temperature
is different for different types of matter.
One familiar example for children is a snowman. A snowman is made of snow, which
is actually frozen water. Once the temperature drops below zero, the water freezes, or
solidifies, into solid matter, ice. When the temperature rises above zero, the ice, or
solid matter, melts and changes into a liquid, in this case, water.
When the temperature of water rises to 100 degrees Celcius, the liquid evaporates and
changes into a gas. The water vapour rises into the air, where, as the temperature
drops, it condenses into water or sublimes directly into solid matter, meaning snow.
The process of a solid substance changing directly into a gas is known as sublimation.
4. Properties of substances and acidity/alkalinity
Elements and their compounds all have their own properties. The factors that affect
the properties of a substance include the bonds that hold the structural units together,
the size of the structural units and the shape of the molecules.
Aqueous solutions of substances may be acidic, alkaline (basic) or neutral. Acidity
can be demonstrated using acid-base indicators. The indicators are weak acids or
bases, whose acidic and alkaline form are differently coloured. For each indicator, the
colour change occurs within a specific pH range.
The acidity of lemon juice is caused by citric acid, HOOC-CH2-COHCOOH-CH2COOH. Citric acid is a crystalline hydroxycarboxylic acid, which dissolves well in
water. Citric acid is particularly found in lemons, currants, rowanberries,
lingonberries and cherries. Citric acid and its salts, citrates, are used in the soft drink,
food and pharmaceutical industries.
Baking soda, sodium bicarbonate (NaHCO3), is an alkaline substance.
In this activity, we will use litmus as the acid-base indicator. The pH range for colour
changes in litmus is approx. 4.5 - 8.3. In an alkaline solution, the litmus is blue-violet,
and in an acidic solution, it is red. Natural indicators that can be used like litmus are
red cabbage (Colourful chemistry) and blueberries.
Litmus is a mixture of colourful, organic components which can be separated from
various lichens, the most common of which are Lecanora tartarea and Roccella
tinctoria. The lichens are ground, treated with K2CO3 and ammonia and left to
ferment. The achieved substance is mixed again with colourless components such as
limestone and gypsum. The active components of litmus are erythrolitmin,
spaniolitmin and erythrolein, all heterocyclic derivatives of phenoxazine.
The indicator strips, which are also used, for example, in determining acidity in
Heureka's Water analysis, are strips of paper that have been saturated with a particular
indicator solution.
The acidity of the solution, or its pH value, is determined by the concentration of free
hydrogen ions (H+) in the solution. The higher the concentration, the lower the pH
value. An acid releases H+ easily, and a base easily accepts it. A strong acid is not
strong in concentration, but refers to an acid that protonates in water, such as HCl.
The conjugated base (A-) of a strong acid (HA) is weak. Correspondingly, the
stronger the base is, the weaker its conjugated acid. (NaOH)
5. Chemical reactions between substances
We are constantly surrounded by chemical reactions. Chemical reactions are highly
diverse and occur in different ways; some happen very slowly, while others occur
with explosive speed.
A tale of substances
"Substances are like third grade children. Some are good friends with each
other and these types of substances form compounds. Others do not get along
with each other at all and they easily come into conflict. The conflict between
substances may even result in an explosion."
When baking soda is added to water and then mixed with lemon juice, a chemical
reaction occurs. The chemical reaction creates a new substance, which is in a different
state from the original substance. A gas called carbon dioxide is created.
2 NaHCO3 --> CO2 + H2O + Na2CO3
In a gaseous state, the structural units of the substances – atoms, molecules and ions –
move almost completely freely, because they have weak interactions with one
another. The result of this is that the amount of gas is not in a concrete shape or
volume, but strives, rather, to continually expand. This creates pressure. In a closed
environment, such as inside a film can, the pressure builds up and causes the top of
the can to pop open.
6. Aqueous solutions and dry ice
The task of a chemist may concern the production of substances and mixtures of
them. The production of food and other perishables is chemistry at its best.
In the Bubbling chemistry activity at Heureka, guests produce Science Centre
Lemonade. The Finnish encyclopaedia, Facta 2001, provides the following
information regarding soft drinks, or lemonades:
Soft drink is a general name given to mineral waters or drinks meant simply for
enjoyment, but not including juices. Mineral waters come from either natural
mineral water sources or they are produced by adding mineral salts to purified
water. Mineral water salts are primarily alkali and alkaline earth metal chlorides,
carbonates, sulphates and citrates. In addition to carbon dioxide released from
carbonates, carbon dioxide in gas form is usually added to mineral waters during
the bottling phase. Sweet soft drinks are produced from a combination of water,
sugar or other sweetener and fruit juice or aromatic preparation. Benzoic and
sorbic acid are used as preservatives in sweet soft drinks. The tart or sour flavour
in sweet soft drinks is created by adding fruit acid, typically citric acid and
carbon dioxide that is added to carbonated drinks. Many soft drinks have colour
additives such as food colouring, sugar colours, carotenoids or anthocyanins, in
addition to containing artificial colourings. Artificial aromas may only be used to
flavour soft drinks that are sold as lemonade. For example, citrus fruit drinks
(‘jaffa’) and cola drinks are not considered lemonade-type soft drinks. The flavour
of cola drinks comes from the cola nut and other plant extracts. They generally
also contain caffeine. In Anglo-Saxon countries, in particular, drinks that are
flavoured with natural aromas and aromatic bitters, such as quinine, are quite
popular (e.g. tonic and bitter lemon).
The ingredients of our Science Centre Lemonade are water, sugar, food aromas, food
colourings and dry ice.
The dry ice used by Heureka is supplied by Oy Aga Ab. Information about dry ice is
available at the company's website www.aga.com.
Carbon dioxide (CO2) is an anhydride of carbonic acid (H2CO3); the density is
1.9768 kg / m3 (NTP), m.p. 216K (-57 ºC) (assuming a pressure of 516.8 kPa) and
b.p. 194.6 K (-78.5 ºC). Carbon dioxide can be condensed into a liquid at 293 K (or
20 ºC) and a pressure of 5.725 MPa. This liquid has a density of 766 kg / m3. As the
pressure decreases, the liquid evaporates quickly and removes enough heat for the
remaining part of the liquid to 'freeze' into a solid so-called carbon dioxide snow.
White dry ice is produced by pressing the snow under pressure. The dry ice then
sublimes and vigorously takes energy from its surroundings. CO2 causes suffocation
if its percentage in the air is higher than 8 per cent.
In laboratories, dry ice is produced from marble and hydrochloric acid. Carbonic acid
is an unstable, weak acid that is formed in solution when carbon dioxide dissolves in
water. The amount of carbonic acid in the solution corresponds to 0.1 % of the
amount of the dissolved carbon dioxide. Carbonic acid forms normal carbonate salts.
Acids release the carbonic acid from its salts, and it breaks down into carbon dioxide
and water.
Before talking about carbon dioxide, tell the children about the primary three states of
matter.
All matter can be in the form of a gas, liquid or solid. Gas condenses into a liquid,
which solidifies and turns into a solid. The solid then melts back into a liquid and
sublimes into gas, which, in turn, changes back into a solid. The circle is complete.
We refer to a certain state as the NTP, normal temperature and pressure. This state has
a temperature of 0 ºC or 273.15 K and a pressure of 101.325 kPa. Each substance,
however, has a specific 'normal' state; in other words, not all the substances appear in
all forms under these conditions.
When you show the dry ice, make sure to circulate past all of the tables, because it's
very fascinating to see. The relevance of the name 'dry ice' can be demonstrated by
holding the ice on a piece of paper towel; the paper towel does not get wet. Tell the
children about freezer burn and remind them that dry ice should not be handled with
bare hands.
When dry ice is place in water, the water will start to bubble. These bubbles are
carbon dioxide gas subliming from the ice. There are also water crystals moving
inside the bubbles.
You can also present dry ice using the following methods:
Option 1: Stretch a balloon over the opening of a soft drink glass, so that the carbon
dioxide gas and frozen water crystals fill the balloon and make it heavy.
Option 2: Do not use the balloon at all, but show the formation of carbonic acid using
litmus (litmus + water + dry ice). Allow the children to try to figure out what the
white bubbling substance is. It runs down because it is cold and heavy frozen water.
Water vapour, on the other hand, is hot and rises. This is a familiar concept to anyone
who has boiled water or has slept in a bunk bed. The white bubbling substance is
definitely not smoke, because nothing is burning.
Frozen water in this form is an exciting and astonishing sight, and, as a matter of fact,
it's also a sight that we admire almost daily --> clouds.
Option 3: The formation of carbonic acid can also be observed using only a balloon.
Once you have let carbon dioxide gas and water crystals flow into the balloon, insert
an indicator into the balloon. Then observe the changed colour of the indicator as it
exits the balloon.
7. Tools and ingredients required
Each pair of participants is given a kit containing the following tools and ingredients:
– 100 ml lemon juice bottle (dilution in water 1:1)
– 100 ml litmus bottle (1g litmus / 1 l water)
– 100 ml aroma bottle
– food colouring, 3 containers (yellow, red and blue)
– sugar jar (granulated sugar)
– baking soda
– spatula for mixing the ingredients
– one large and one small plastic measuring spoon.
The following items should be placed on the wire rack in the centre of the table for
each pair:
– test tube holder with two test tubes (preferably of the same length)
– 250 ml Erlenmeyer flask, which contains water, and two plastic pipettes
– 250 ml glass decanter
The instructor also has
– film cans
– effervescent tablets.
8. The process
1. Enquire and tell briefly about the object of research in chemistry (substances) and
the work of chemists (to study the properties of the substances and their reactions).
2. Describe the different states of substances, using the snowman-puddle-water
vapour example.
3. First study acidity. Ask whether the children can think of any acid substances and if
they know what the opposite of acidic is. Ask them to take the test tube holder in front
of them and to turn the test tubes the right way up.
4. Ask the children to open their kits and remove the first item; a bottle with a yellow
dot on the cap. This bottle contains lemon juice. We pour about two centimetres of the
juice into one of the empty test tubes until it reaches the middle level (show the
correct amount). Ask the children to replace the bottle cap and place the bottle back
into the correct place in the kit. NOTE! Remember them to do this each time they use
something from the kit.
5. Ask the children to remove the container with the red lid (containing baking soda)
and the smaller of the two measuring spoons from the kit. Measure out one spoonful
of the baking soda from the container and place it in the empty test tube.
6. Ask the children to remove the flask containing water (the world's most important
substance!) and the two pipettes from the wire rack. Demonstrate how the pipette
works: the end of the pipette is submerged in the water and the bulbous end is pressed
flat. Then, while keeping the end under the water, release the bulb. This sucks water
into the pipette. Lift the pipette out of the dish and squeeze the water into the test tube
containing the baking soda. This can be done two times (so that each partner gets a
chance) or so that the amount of water is at least as much as the lemon juice.
7. The next step is to figure out the acidity of the substances in the tubes. Ask the
participants to take out the litmus bottle, whose cap is marked with a blue dot. Briefly
talk about litmus and other indicator substances. Add 5-10 drops of litmus straight
from the bottle into each of the test tubes. Ask the children to tell what happened and
to figure out which of the substances is acidic. Litmus turns red when mixed with
lemon juice, therefore the lemon juice is acidic. When mixed with a mixture of water
and baking soda, litmus does not change colour.
8. Tell the children that they are going to produce a substance in the next experiment,
and they will also study what happens when an acidic and an alkaline substance are
mixed together (neutralization). Ask the participants to pour all of the lemon juice in
the test tube into the test tube containing the baking soda. The baking soda tube can
first be carefully shaken to ensure that the baking soda mixes well with the water.
After adding the lemon juice, bubbles appear and the solution changes colour. The
solution is no longer acidic, but is neutralized and turns blue-violet. The bubbles
contain carbon dioxide gas. Why does the surface of the substance rise in the tube as
the bubbles are being created? The reason is that gas has no distinct shape or volume
and it strives to continually expand.
9. A film can rocket can be made now or at the end of the activity. Tell the children
that we want to send up a rocket using gas. Put two pipettes of water into the film can.
Add one half of the effervescent tablet and shut the film can carefully (and quickly!).
Place the film can onto the plastic dish with the lid facing down. Step back and begin
the countdown. Gas forms inside the can and as the gas expands, the pressure builds
up. If the pressure increases enough, the can will pop open and the ‘rocket’ will shoot
up in the air.
10. The final stage of the activity is to make Science Centre Lemonade. Ask the
children what ingredients belong in soft drinks. Write the ingredients on the board;
they include water, sugar, colouring, flavouring, carbon dioxide bubbles and carbonic
acid. Tell the children to take out the large measuring glass (glass decanter) to hold
the soft drink and the metal spatula for mixing.
- Take 150 ml of warm water from the tap.
- Add 1 tsp of sugar (the larger plastic spoon).
- Add 5 drops of aroma straight from the bottle.
- Food colouring: Ask the children to place the blue, red and yellow food colourings
on the table. The children can decide what colour lemonade they want to make. The
colours may also be mixed. Colouring is added to the drink in small portions and
mixed at the same time until the colour is clearly visible.
At the end, the instructor takes out the dry ice and places a small piece of it in the
glasses of each couple. NOTE! Tell the children that they may not place their fingers
in the glass--the ice may not be touched--and the glasses must remain on the table.