Red cabbage indicator is a purple-coloured solution that is used to test whether substances are acid or base. Red cabbage that is often found in homes can be used to prepare a solution that acts as a pH indicator. The cabbage basically contains a pigment molecule called flavin or anthocyanin that changes colour depending on the acidity of the solution.
Normally, the purple solution turns red in colour when it combines with something acidic and it turns bluishg-green in colour when it combines with a base. If the substance does not cause the colour to change then it is mostly neutral.
Red Cabbage Indicator pH Colours
Below are the different pH levels and the colours that are obtained during the red cabbage indicator test.
| pH | 2 | 4 | 6 | 8 | 10 | 12 |
| Colour | Red | Purple | Violet | Blue | Blue-Green | Greenish Yellow |
Let us conduct an experiment and observe the results.
Aim
To determine which chemicals are bases and which are acids.
Apparatus Required
- Water
- Red cabbage leaves
- Colanders
- Vinegar
- Lemon juice
- Soda(baking soda)
- Detergent
- Glass jars of a similar size
Procedure
- Cut the cabbage leaves into small pieces.
- Boil separate cups of water as they will be required to submerge your pieces later on.
- Place the cabbage pieces into a bowl and pour the water in the bowl. Keep it for several minutes so that the cabbage pieces get soaked. You can also use a mixer to grind the leaves and obtain a solution.
- If you are not using the mixture then separate the juice from the leaves.
- Take glass jars and place them about two inches apart. Pour every chemical (lemon juice, vinegar, detergent and soda) into each jar.
- Now to determine whether the substance is a base or an acid pour the cabbage juice into each jar. Here, if the mixture turns pink or red the chemical is an acid and if it turns bluish-green the chemical is usually a base.
This experiment can easily be conducted even in the house and can be used to test different substances which are easily available.
Safety Tips
- Since the chemical indicator is used to test acids and bases it is always advised to use safety goggles and gloves especially while dealing with strong or concentrated chemicals.
- Chemicals can be washed down the drain safely with water.
- A neutralisation experiment can also be done along with the test.
Making pH Paper
In addition to the solution, pH paper strips can also be created using red cabbage using the steps given below:
1. Firstly, use a filter paper (or coffee filter) and dip it in the concentrated solution obtained from red cabbage.
2. Soak it for some time and later take the paper and dry it.
3. Once it is dried, cut the paper into small strips and they are ready to be used for testing the pH of different solutions.
4. Pour a drop of liquid on the test strip and see what colour is obtained. The strip also turns either red or green depending on whether it is acidic or basic.
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