Credit: Techniquest Teacher Workshop (Dr Clare Coombes and Dr Sue Cavell)
British Council
Hong Kong Science Museum
Techniquest
1

There are a host of chemical principles that can be simply demonstrated using items commonly found in the home, most especially in the kitchen. We have focused on 3 areas that are commonly studied and have selected some simple experiments that can broadly be placed into one of these groups. In addition, we have also included two longer investigations, which require a more focused approach and the application of some basic chemical principles to solve a particular problem.
2

Materials
Experiments 1: Slime
Experiments 2: PVA Potty Putty
Experiments 3: ‘Gunge’ Ball
Experiments 4: Super Soakers
Experiments 5: Plastic from Milk
Simple Chemical Reactions
Experiments 1: A Simple Reaction
Experiments 2: Blast Off!
Experiments 3: Ghostly Graffiti
Experiments 4: Ink from Tea
Experiments 5: Yeast Balloons
Properties of Liquids
Experiments 1: Egg Colouring
Experiments 2: The Floating Golf Ball
Experiments 3: Lava Lamp
Experiments 4: Milk on the Move
Longer Investigations
Investigation 1: Use it Again
Investigation 2: The Mystery
Bibliography
page
4
6
8
10
12
14
16
17
18
19
28
30
31
20
22
24
26
3

You will need: Cornflour
Water
Container
Stirrer
Simply add water to the cornflour, never the other way round. Aim to produce mixture with a runny consistency.
Investigate stirring the mixture slowly at first and then more quickly. Try hitting the slime with your fingers. How does it feel? Repeat the hitting process, but this time in slow motion.
4

Every time the mixture is stirred, hit or rolled, no matter how hard or gently, a force is being applied. Cornflour and water is an example of a mixture that behaves differently on how suddenly or slowly this force is being applied. The cornflour powder does not dissolve in the water but remains as tiny little grains of solid suspended in the water. When there is just the right amount of water, these grains are closely packed together but there is a thin layer of water between them that allows them to flow past each other, even if the mixture is stirred or poked gently (i.e. the force is applied slowly). This makes the mixture runny…like a liquid. However, fast stirring or hard hitting (i.e. a sudden force) causes the solid particles to push together, squeezing the water, the grains find it difficult to push past each other making the mixture thicker and more like a solid.
5

You will need: PVA glue
Borax solution (CAUTION: Borax is harmful if swallowed)
Paper cup
Stirrer
Mix 20 cm
3 of the PVA glue with 20 cm
3
of water in a paper cup. Add food colouring if required and then 5 cm3 of borax solution. Stir, remove from cup and knead between fingers.
Investigate the properties of your potty putty. Try pulling gently and then pulling it quickly. Roll some into a ball and drop it on the floor. What happens if it is left undisturbed on the work surface for awhile? Take a small piece of it and hit it with a hammer. Take another piece and press it with your thumb.
Further Investigations
The behaviour of your potty putty can also be compared with plasticine or blu-tack.
Commercial potty putty can be bought in toyshops and a comparison of the properties of commercial and homemade potty putty can also be made.
6

Like the cornflour slime, the potty putty is different to ‘normal’ fluids. We can imagine it to be made up of long particles that are firmly linked to each other. Potty putty is a polymer made by a chemical reaction. A polymer is a substance that consists of long chains of repeating units. When PVA (polyvinyl acetate) and Borax are combined, the polyvinyl acetate chains are linked together in a 3-dimensional arrangement by borate ions to produce a thick, sticky polymer.
How the putty behaves depends upon the force applied to it. When dropped onto the floor, the sudden force causes the particles to bend and then spring back, i.e. the putty will bounce. If a strong force is applied, such as being hit with a hammer, some of the particles separate and the putty shatters.
If a force is applied slowly, as in stretching, the particles separate more and form new links, so that the putty flows.
Although commercial potty putty has very similar properties to home-made putty it is not a polyvingl acetate polymer but a silicon (Si) polymer. It was discovered by accident in the 1940’s during attempts to make synthetic rubber. Although no engineering application could be found for it, it was marketed as a toy because its such fun (and safe) to play with!
7

You will need: Powder, e.g. Baby powder
Oil-free moisturizer
PVA glue
Saturated Borax solution
Water
Food colours
Paper cup
Stirrer
Measure out one level teaspoon of talcum powder and place it in the cup. And 10 cm
3
of moisturizing lotion, 10 cm
3
of PVA glue and 10 cm
3 of water. Stir well to mix the ingredients. Add a couple of drops of food colour and stir. Add 5 cm3 of borax solution and stir. Remove the ‘gunge’ from the cup.
Investigate the properties of the ‘gunge’ ball.
8

Cornflour becomes thicker when it is stirred, but some liquids can behave quite differently. Tomato sauce, which has a high starch content, will not flow easily from an upturned bottle. When the bottle is tapped the loose forces binding the starch can part and the sauce flows like any liquid, after which the forces reform.
Other examples include butter and margarine.
Although initially firm, a knife sliding over the surface will soften the butter, which will then immediately harden again. The process is repeated when spreading onto bread.
Similarly, a ball-point pen contains ink which will not flow when the pen is inverted. When we write, the small rolling-ball applies a sideways force to the ink, causing it to flow onto the paper.
Without this force the ink becomes thicker on the paper and hopefully will not smudge!
9

You will need: Ultra absorbent nappy
Scissors
Plastic bag
Paper cup
Stirrer
Water
Carefully take the nappy apart; pull or cut the internal cotton into smaller pieces.
Place these in a plastic bag, seal and shake well. Discard the cotton and collect the super-absorbent powder, which collects at the bottom of the bag.
Safety: The super-absorbent material may be a mild skin irritant. Please wash hands after using this material.
Investigate how much powder was collected and how much water the powder can absorb.
10

The inner layer of the nappy contains small super-absorbent polymer crystals of sodium polyacrylate. The ultra-absorbent powders were originally intended for use in off-shore oil drilling operations. These synthetic drilling fluids could absorb up to
2,000 times their weight of water. It’s a little less for the material in the nappies, but something of 80 times its weight in liquid is fairly typical. However, there is a downside to the invention of the super-absorbent nappy-whilst undoubtedly more comfortable for the baby and more convenient for parents they are causing environmental problems. As used nappies cannot be recycled, they are disposed of in landfill sites and as they are not biodegradable the space required to bury them is ever increasing!
11

You will need: Milk
Paper cup
Stirrer
Vinegar
Kitchen roll or coffee filter paper
Pour about 1/4 of a cup of warm milk into a paper cup. Add a tablespoon of vinegar and stir. When the solid curds separate, filter using a paper towel or coffee filter.
Pull the curds from the paper and gently squeeze the excess whey into the cup.
Leave the solid to dry and compare with a fresh sample.
Further Investigation
Finding the best conditions for production with different dilutions of milk, quantities of vinegar or temperatures would make an ideal class investigation.
The curds can be changed very easily into a simple white glue. Just add a pinch of sodium bicarbonate to the solid and stir well.
Try sticking various surfaces together to see how well the glue performs (allow 6 hours for the glue to dry completely)
12

Milk contains water, fats and a protein called casein. The protein is usually dissolved, but when vinegar is added, a chemical change takes place and the casein molecules clump together. This process of chemically changing a protein into a solid is called ‘denaturing’ a protein and is used to turn milk into cottage cheese and cheese. By treating this product with formalin, a hard plastic can be produced from casein to form casein to form buttons and knitting needles!
If sodium bicarbonate is added to the curds, any remaining acid (vinegar) is neutralised and the casein will act as a glue as these large molecules will stick to each other and to the surfaces being glued.
13

You will need: A teaspoon of sodium bicarbonate
Vinegar (white is best as the colour doesn’t mask the colour of the indicator)
Red cabbage juice indicator
A few drops of dishwashing liquid
Water
Clear plastic cup
Place the sodium bicarbonate in the clear plastic cup.
Add a slight amount of water to dissolve some of the powder and then add a few drops of indicator to see the colour of the indicator in the basic solution. Add a few drops of washing up liquid to this mixture.
Add a few drops of indicator to the vinegar.
Add the vinegar to the sodium bicarbonate.
14

The reaction between sodium bicarbonate (NaHCO3) and Vinegar (CH3COOH) is the standard reaction between a carbonate and an acid with the production of a salt, water and carbon dioxide gas being the net result. If a simple homemade indicator is added then the neutralization reaction can be followed by the changes in colour of the indicator. The production of CO2 gas is also visible as the reaction fizzes as it progresses (the washing-up liquid is added so that a more visible foam is produced by the gas generated).
Sodium bicarbonate is a common ingredient used mainly in the banking of cakes.
When added to a cake mixture, the heat from the oven causes the sodium bicarbonate to break down releasing carbon dioxide gas. The gas trying to escape forces its way through the mixture of sodium bicarbonate and cream of tartar (tartaric acid), which in the presence of moisture react together to again liberate carbon dioxide.
However, this liberation of gas from this reaction can be used to much more effect in the following adaptation of this experiment.
15

You will need: Empty film canister with lid
Antacid tablet CAUTION: These may contain aspirin or other pharmaceuticals which children under 16 must not ingest – careful adult supervision required)
Vinegar
Take an empty film canister and half fill it with vinegar. Place on a hard surface.
Take half an antacid tablet and hold it under the lid whilst quickly popping the lid firmly on the canister. The tablet will drop into the vinegar.
Stand well back and watch the lid fly off the canister (you may have to wait for a result so don’t return to the canister if nothing has happened after a few minutes).
The main ingredient of an antacid is base, usually sodium bicarbonate. Adding vinegar causes the neutralization reaction to occur leading to the release of carbon dioxide gas. The build up of gas causes the pressure in the canister to increase until it is great enough to force the lid off the container!
Antacids are used to help relieve ingestion, which is caused by a build up of acid in the stomach. The sodium bicarbonate in the tablet neutralizes this excess acid.
However, carbon dioxide gas is also produced as part of this neutralization reaction in the stomach, hence the unfortunate side effect of taking an antacid!
16

You will need: Paper
Lemon juice
Cotton bud
Desk lamp
Write a message on the paper using the cotton bud dipped in the lemon juice and leave to dry.
Hold the paper up to the light bulb (making sure that the bulb has had sufficient time to get hot) and watch the message slowly appear!
This simple demonstration illustrates two types of chemical reaction, thermal decomposition and oxidation. Lemon juice contains amongst other things, citric acid, which is sometimes used as a preservative in food. In lemon juice, the citric acid stops some of the other substances in the juice from oxidizing and turning brown.
However, citric acid is decomposed very easily when heated. The heat from a light bulb is sufficient to decompose the citric acid in the lemon juice and so the writing starts to appear as the oxidation of the other ingredients stats to happen.
This oxidation can also been seen when some fruits such as apples, pears etc (i.e. non citrus fruits) are cut open and left exposed to the air. An ages old remedy for stopping the browning of such fruit is to sprinkle it with lemon juice.
17

You will need: 2 Iron Tablets (iron 50mg as iron(II) sulphate)
CAUTION – extremely toxic if swallowed in excess
2 Teabags
Hot water
Drinking straws
Heatproof beaker
Paintbrush
If the iron is in the form of capsules then break open both capsules and place in a heatproof breaker. If the iron is in solid tablet from then crush both before placing in the beaker. Add two tea bags.
Carefully add about an inch of boiling water (CAUTION) and leave to cool for about
5 minutes. Observe what happens as the water is added. THIS SOLUTION MUST
NOT BE DRUNK!
In the meantime, take a plastic drinking straw and fashion a pen from it by cutting one end into a sharp, tapered point.
When the ink has cooled, remove the teabags and write with your ‘teabag’ ink using your ‘pen’. If this proves too difficult to use, write with the paintbrush instead.
CARE: THIS INK CAN PERMANENTLY STAIN CLOTHING!
18

A reaction occurs between the tannic acid (from the teabags) and the iron, resulting in a substance, which is black and so finely divided that it says suspended in the water.
The straw pen works by drawing up small amounts of ink by a process called capillary action and then transferring some of the ink to the paper through the fine point and as the water dries, the black substance is left behind on the paper.
19

You will need: A plastic drinks bottle with lid
Balloon
Active dry yeast
Water
Teaspoon measure
Fill the bottle 1/3 full with warm (not hot) water.
Add about 3 teaspoons of sugar.
Add 2 teaspoons of yeast.
Screw the lid on the bottle and shake well to mix and dissolve the yeast and sugar.
Remove the lid and stretch the mouth of the balloon over the mouth of the bottle.
The balloon should start to inflate and foam should be produced in the bottle. The reaction that is taking place inside the bottle is FERMENTATION. The yeast, which are tiny living organisms, break down the sugar into alcohol and carbon dioxide gas.
This gas produced then inflates the balloon and creates the foam.
Fermentation is a reaction that has been used for centuries is the production of foods such as bread and alcoholic drinks such as beer.
20

You will need: 4 eggs
Water
Vinegar
Salt
Sugar
Food colouring
Water
Sticky labels
4 clear plastic pint glasses
Jug
3 stirrers
Teaspoon measure
Tablespoon measure
Take the 4 clear plastic pint glasses and label as follows: water only, vinegar, vinegar and salt, vinegar and sugar.
In a jug mix 2 teaspoons of food colouring with 500ml of water and then pour 1/4 of this mixture into each of the four glasses.
Add 1 tablespoon of vinegar to each ‘vinegar’ bowl and 1 tablespoon of salt and 1 tablespoon of sugar to the appropriate glasses. Stir to mix.
Place one egg in each of the glasses, making sure the egg is completely covered in the solution.
Leave for ten minutes before carefully removing each egg and rinsing 4 times with water. Leave to dry, noting which egg was in which solution.
21

The amount each egg was dyed by the food colouring depended on the solution it was in. The presence of charged particles (ions) in the solution has an effect n how much food colouring is taken up by the eggshell.
A thin layer of protein molecules called the cuticle covers the surface of an eggshell.
This layer is neutrally charged and remains so when placed in a neutral solution such as water. If however, an acid (vinegar) is added, the protein molecules of the cuticle become positively charged.
Food colouring molecules generally from negatively-charged ions in solution and so are much more attracted to the positively-charged eggshell formed in an acidic solution, (meaning that the egg takes up more of the dye) than to the neutral eggshell in water only.
If, however salt is also added to a water/vinegar solution, the egg does not become so coloured. This is because the negative chloride ions produced when salt (NaCI) dissolves in water are also attracted to the positively charged eggshell and so interfere with the food colouring ions binding to the surface. The presence of sugar on the other hand, has no effect as it does not interfere with the attraction between the egg surface and the food colouring.
22

You will need: A tall, clear container
Golf ball
Salt
Water
Food colouring
Mixing beaker
Jug
Fill the cylinder half full with water and then pour this into the mixing beaker. Drop the golf ball in the water (it should sink)
Now add enough salt to the water in the beaker so that the golf ball will float. Remove the ball and now put in the cylinder. Pour the salty water back into the cylinder.
Fill a jug with water and add a few drops of food colouring. Carefully, pour this coloured water into the cylinder taking care not to disturb the salty water. Fill to the top of the cylinder.
Mark off on the side of the cylinder the position of the golf ball and observe over a few days.
23

This is all to do with differing densities. Salty water is much dense than fresh water will sink to the bottom of the cylinder whilst the fresh water will form a layer on top.
The golf ball is denser than fresh water but less dense than salty water and so will float somewhere the two layers meet. After a few days however, the fresh and salty waters will gradually mix (due to diffusion), leaving a solution with an overall density less than that of the golf ball which will eventually sink.
This concept is also illustrated well in how a can of diet coke and a can of regular coke behave when immersed in a tank of water. The diet coke will float much higher than the regular coke and as the volume of the two cans is identical, the density of the liquid inside the cans much account for this observation. The difference in density of the diet drink and the regular drink is explained by the difference in mass is due to the amount of sugar that is contained in the regular coke compared to the mass of artificial sweetener in the diet drink. This can be shown by firstly weighing the can of regular coke. The diet coke is then weighed and sugar is added to the scales until the weight reads the same as for the regular coke. The mound of sugar is how much there is in the regular drink and also illustrates the sweetening power of artificial sweeteners compared to sugar.
24

You will need: A clear plastic pint glass
Vegetable oil
Water
Salt
Food colouring
Fill the glass about 2/3 full of water. Add vegetable oil to a depth of about 5cm.
Add a few drops of food colouring and observe what happens to the drop.
Now sprinkle salt liberally on top of the oil and watch what happens.
Add more salt to keep the action going.
The oil and water don’t mix – they are immiscible – and as the oil is less dense than water it floats on the top. The food colouring is also not soluble in oil and so stays in globules on the surface of the oil.
Salt is also insoluble in oil but because it is more dense than the oil, gravity pulls it down to the bottom of the glass and as it does so, it drags some of the oil with it.
When the salt reaches the water layer it starts to dissolve and the oil blobs are free to rise up again to join the oil layer at the top. The food colouring is also eventually dragged down by the salt, changing the colour of the water layer as it dissolves.
Lava lamps work in a similar way. In the lamp there are two coloured liquids which are immiscible but close in density. As the blobs of one liquid are heated up by the lamp at the bottom, they become less dense and so rise up to the top. Once at the top, they cool down, become more dense and so sink until the process starts all over again.
25

It may also be beneficial to show a simple experiment at this point on how detergents and soaps work. Simply take two jars or plastic bottles with lids and fill both with a layer of water followed by a layer of vegetable oil. To one bottle only, add a few drops of washing-up liquid. Replace the caps and shake each bottle the same number of time before setting down and observing what happens.
Obviously, in the bottle with no detergent the water and oil will eventually settle out into two separate layers again with no mixing having occurred. In the bottle containing detergent, oil droplet, oil droplets remain suspended in the water.
The ability of liquids to mix (their miscibility) depends on the shape and electrical charge of the liquids’ molecules. Liquids that are similar will mix well and those that are very different will not.
Water molecules are small and polar (on part of the molecule has a positive charge and another part has a negative charge) and mix very well with liquids of similar characteristics, for example alcohols. Oils on the other hand, are larger and non-polar
(are neutrally charged all over) and so don not dissolve in liquids such as water. This makes it difficult to wash away grease and oils.
Detergents are able to increase the compatibility between water and oil. This is because detergent molecules contain a small polar water-loving head (hydrophilic) on a long non-polar water-hating (hydrophobic) tail. These water-hating tails surround an oil droplet with their water-loving heads pointing outwards facing the water; to form a unit micelle. In effect the detergent forms a kind of shell around the oil droplet, disguising it and making it more attractive to the water. The micelles are suspended in water enabling the oil to be washed away.
26

You will need: Full fat milk
Skimmed milk
Cream
Food colouring
Washing-up liquid
Cotton buds
3 paper or polystyrene disposable bowls
Sticky labels
Disposable plastic dropper
Label three bowls with the three types of milk and pour the corresponding milk into each to a depth of about 5cm.
Carefully add 2 drops of food colouring to the centre of each bowl taking care not disturb the milk.
Observe the way the food colouring looks in each bowl taking care not to disturb the milk.
Dip a cotton bud in the washing-up liquid and carefully touch the centre of each food colouring drop observing the way the food colouring moves in each type of milk.
27

Milk is mostly made up of water and then equal parts of water and then equal parts of protein, fats and sugar. These days most milk is HOMOGENIZED which means that the fat has been broken up and spread throughout the milk in tiny globules. However, raw milk is UNHOMOGENIZED and has a layer of fat rich milk floating on top of the rest. The milk has to be shaken before it is served otherwise the first sip is of heavy cream.
However, different types of milk differ in how much fat (and therefore water) they contain with cream containing the most fat whilst skimmed contains the least. They way the food colouring spreads on the surface of the different milks acts an indication of how much fat there is. Food colouring is water but not fat-soluble and so the more fat present, the less it will spread.
Adding the detergent has a dramatic effect on the surface of the milk. When in contact with detergent, the fat globules break up and expand across the surface of the milk.
This creates movement in the previously still surface of the milk. Usually this can’t be seen but the presence of the food colouring shows how the ‘skin’ of the milk moves and changes in response to the detergent.
28

The properties of 5 white powders commonly found in the kitchen are investigated and the results used to deduce the identity of a mystery sample of one of those powders.
You will need: Powdered white sugar
Flour
Powdered classroom white chalk
Sodium bicarbonate
Cream of tartar
Vinegar
Tincture of iodine solution
Red cabbage indicator
Water
Ice cube tray
Mystery white powder
Can you devise a series of tests that will distinguish one white powder from another and apply your results to identify what the mystery powder sample is?
29

Kids and Chemistry, Hands-on Activities and demonstrations, The American
Chemical Society
Experiencing Chemistry, Museum Manuals 1 and 2, Oregon Museum of Science and
Industry, 1997
The Science Year Website at www.scienceyear.org.uk
30