Red cabbage juice is a natural pH indicator and is one of the most popular chemistry experiments for children. The indicator changes from purple to bright pink in acids (e.g. lemon juice or vinegar) to blue or yellow-green in bases (detergent, soap). Students can use this pH indicator to classify a variety of safe household chemicals including vinegar, laundry powder and lemonade.
Acids and alkalis
Acids have a sour taste, like vinegar (which contains ethanoic acid) and lemons (which contain citric acid).
Alkalis are substances bitter and soapy substances that react with acids and neutralise them. Soap and washing powder are alkaline.
Acids and alkalis are found in a surprising number of places. Some are edible and are found in foods. Others are very strong and can be harmful, such as the acid in car batteries and the alkali in oven cleaners.
Acids and bases – this experiment uses acids and bases
Natural chemicals – this experiment can be used to introduce the concept that chemicals found in nature can be of use to humans (i.e. as pH indicators). Reactions of acidic and basic substances with an indicator involved colour changes. This experiment can be used to illustrate chemical reactions, which would usually involve colour changes.
Make an indicator: Do you know that Sydney water doe up to 70 tests on your water to make sure it is safe?
An indicator is a chemical that changes colour in acidic, basic or neutral substances. Here is a fun way to compare substances in your home by making a natural indicator using red cabbage.
SAFETY: Adult supervision is needed for preparing the cabbage water. Follow the safety precautions on household substances before testing them.
WHAT YOU and HOW to make the indicator: Powerpower point: red_cabbage_indicator