Changing colour with cabbage
Create a colour-changing liquid and gorgeous artworks with some cabbage and simple household items while learning about acids, bases and pH.
Red cabbage and some other plants contain a pigment called anthocyanin that gives our cabbage it’s colour. This pigment has the ability to change colour and is an example of a pH indicator- something that can detect acids and bases. Armed with a variety of kitchen ingredients you’ll soon be amazed by the gorgeous colours cabbage juice can create and learn which things in your home are acidic or basic.
For this activity you’ll need about 4 red cabbage leaves, some water, a blender, smoothie maker or stick blender, some white vinegar or lemon juice and bicarbonate of soda, glasses or small white bowls, and a variety of other kitchen items for testing such as lemonade, juices and soap.
- Set up an area to work where you can be a bit messy and wear clothes where it’s ok to splash some colour on.
- Ask an adult to help you with taking your cabbage leaves and putting them in a blender with about two cups of water.
- Blend the mixture until you have purple cabbage juice.
- Pour it through a strainer to filter out all of the big chunks of cabbage, saving the liquid but throwing out the solids.
- Pour a little cabbage juice into 3 glasses or small dishes.
- Add a spoonful of your vinegar or lemon juice to one glass and observe what happens.
- Add half a teaspoon of bicarb soda to another glass. What colour do you have now? Compare both of these to your glass of plain cabbage juice.
Vinegar, otherwise known as acetic acid is an example of an acid. Other acids can be much stronger or even weaker. At the opposite end we get substances that are alkaline (otherwise known as bases) such as bicarbonate of soda. The pH of a substance is measured on a scale of 0-14, with acids measured closer to 0 and bases towards 14. If our substance is neither acidic or alkaline and has a pH of about 7 we say it has a neutral pH. Tap water is usually pretty close to neutral.
Our cabbage juice is indicating if something is acidic, neutral or basic by changing colour. Other indicators may tell us the same thing but with a different variety of colours. There are also electronic pH indicators that give us more accurate results but aren’t nearly as much fun to look at. Knowing the pH of something is very useful as it can affect many parts of our lives including how plants grow in soil, how to clean our houses and how to keep our teeth healthy.
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