Imaginative Teaching Resources & Inspirational Career Ideas from the Chilled Food Industry
Most cabbage is green. Right? Wrong! We can change the colour of cabbage using water, vinegar or washing powder. Just don’t eat it after you’ve experimented with it!
You’ll need: red cabbage, vinegar and some washing powder.
Put three or four large red cabbage leaves in a blender half filled with water. Blend until purple.
Pour the liquid into three glasses or jars (sieve out the chunks!).
Line up the jars against a white background. Label one as the colour reference and don’t add anything to it (so you can compare the results).
Pour vinegar (acid) into one glass and give it a stir – what colour does it go? It will go red.
Add a spoonful of washing powder (alkali) to the second glass and stir – what colour does it go? It’s gone green.
Why the colourful results?
The purple cabbage water reacts differently, depending on whether you add an acidic substance or alkaline one. Acids and alkalis are measured on something called pH scale. Acids have low pH and alkalis have high pH.
The cabbage is neutral when you start so adding acid or alkali moves it along the pH scale and the pigment (the colour) changes to match.
The pH scale is a fascinating scale that identifies how close something is to an acid or alkali and can be used to test the pH of all types of liquids.
See how something tastes and can you then test its pH – what is lemon juice?
Here comes the science…
The red cabbage contains a water soluble pigment called anthocyanin that changes colour when its mixed with acid or alkali substances – the pigment turns red in acidic environments with a pH of less than 7 and blueish green in alkaline environments greater than pH 7.
How about a trip back in time to the 1970s? Who remembers lava lamps? Let’s make our own.
All you need is a clean jam jar, food colouring, oil and salt
Fill the jam jar with water till ¾ full. Add a few drops of food colouring
Add about 2 tablespoons of oil – can you see the oil floating on the top of the water – shake it – does it mix?
Let it settle and then sprinkle salt until the oil bubbles start to sink and then watch as they rise to the surface again – like a lava lamp!
Tell me about the science….
Oil and water are immiscible liquids – they don’t mix together – no matter how hard you shake them! Add salt, it clings to the oil, taking it to the bottom, as it falls the salt dissolves in the water, the oil is now lighter than the water floats back to the surface.
Think of your salad dressing. The oil and vinegar separates out and you shake the bottle to mix it up. It’s the same reaction.