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I distinctly remember, as a rather curious four year old, spending an overly long time on tip-toes at the bathroom basin, mixing together my mother’s foundation, perfume and concentrated tooth powder. I wanted to see what would happen.
I imagine many children have had the same sort of early adventures in chemistry. As teachers of science, we can capture this inquisitive spirit and give our children permission to do what is normally unthinkable. Let’s mix it up and, like George, ‘touch the edge of a magic world’ with just a few kitchen cupboard ingredients.
This is a science experience based on trial and error and having a go, with close observation and recording. There is, of course, a lot to be learnt about how materials behave along the way, but the end result is flexible. Most of these activities can be made more or less challenging depending on the age of the children or how much emphasis you place on accurately measuring and recording.
George’s medicine for his gran is a liquid so let’s start there. We can talk about what makes a liquid liquid, how it is different from a solid, and whether all liquids are the same.
Not all of them mix together completely. Give children a range of typical kitchen liquids, including cooking oil and water. Oil is less dense than water so will always float on top.
Ask children to pour some oil into a plastic tumbler half full of water. What do they notice? Drop a few beads of food colouring onto the top of the oil. What happens?
Push the drops further into the oil. What happens when they reach the water? Food colouring is water based so will not mix with oil; it will stay in coloured droplets until it is in contact with the water where it will mix completely.
I love the magic of seeing colours change in a science experiment. Making natural indicators (chemicals that change colour when mixed with acids or alkalis) provides a host of opportunities to investigate this. For a ‘wow’ starter activity, you’ll need some liquid universal indicator.
You can get this online or from your local secondary school. Mixed in water with an acid such as lemon juice, the indicator turns red. It will be green if the solution is neutral and blue if alkaline. Start with a lemon juice solution (red) then add some commercial anti-indigestion medication. Swirl it around and watch the rainbow of changes as the alkaline medication gradually neutralises the acid.
Red cabbage makes a fabulous homemade acid indicator. It contains anthocyanin, a pigment that changes depending on whether it is in an alkaline or acid solution.
Chop up some fresh red cabbage and steep it in hot water for about half an hour or until the water turns dark purple. Adding this indicator to an alkali such as bicarbonate of soda turns it green, while an acid such as vinegar will turn it a deep pink.
Experiment with cream of tartar, sodium bicarbonate, soap, dishwasher powder (under close supervision as it is quite strong), lemon juice or white vinegar. Stay safe – avoid kitchen cleaners and bleach! Challenge yourself – what colour do you think the indicator will show when mixed with egg whites?
You can also use cabbage indicator for a type of ‘magic painting’. Make a ‘wash’ with the cabbage water over some heavy white paper and allow it to dry slightly. Now paint a design using lemon juice. This will turn the pale purple paper a shocking pink. Rubbing a wet paintbrush over a dishwasher tablet and using this as paint will create a vibrant jade green.
When an acid like vinegar is mixed with bicarbonate of soda or other alkalis, there is a chemical reaction.
This is a bit like the chemical equivalent of an anagram, with atoms moving around like letters in a word. The molecules (particles) mix together and swap atoms around to make different molecules – in this case producing three different substances where there were originally two, one being the gas carbon dioxide.
You can capture this gas by mixing the chemicals in a narrow-necked bottle and quickly covering the bottle opening with a balloon.
As the gas is produced by the chemical reaction, it will inflate the balloon – just as George’s original medicine blew his Grandma up.
You could draw Grandma Kranky’s face in pen on your balloon and watch it grow as the balloon inflates. Who can make the biggest granny?
George couldn’t remember how to make his first medicine again because he didn’t write anything down. How will we remember all of our various concoctions? Can we be systematic in our recording? What happens if we increase the amount of acid, or increase the amount of alkali? What is the mixture that makes the most gas?
Another sort of fizz is that produced by yeast as it grows. Try mixing dried yeast with different proportions of warm water and sugar. What combination produces most growth in this living organism? If you mix your yeast, sugar and water in a measuring cylinder, it becomes easy to compare how far the yeasty foam has travelled up the scaled container.
Now we’ve experimented with all of these marvellous changing materials, it’s time for a challenge. Here are a few suggestions – create a medicine that has three layers, one of which needs to fizz; a medicine that changes colour when stirred; a concoction where two liquids added together makes a liquid and a solid; a potion that turns egg whites green. Above all – have fun finding out!
Foaming Fizzy Potion
What you’ll need:
• Bicarbonate of soda
• Washing-up liquid
• Lemon juice
• Food colouring (optional)
• A plastic cup or mug
Inspired by Roald Dahl’s terrific tale, try a class experiment from new book George’s Marvellous Experiments (£7.99, Puffin).
Deborah Herridge is an author of Pearson’s new ‘Science Bug’ programme and ‘Progress and Assess’ assessment tasks. She is also a partner in Primarily Science, delivering primary science CPD nationally and internationally.
You can find even more free Roald Dahl resources here.
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