Red Cabbage Indicator

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Red Cabbage Indicator - Practicals Experiment

Indicators are chemical compounds that can be added to a solution to determine whether the solution is acidic, basic or neutral. A red cabbage pH indicator is a purple-coloured solution that is often found in homes and can be used to prepare a solution that is used to test whether substances are acid or base.

The cabbage contains a pigment molecule called flavin or anthocyanin which changes the colour depending on the acidity of the solution. Now let’s conduct a red cabbage indicator experiment to observe the results.


Aim

To determine the chemicals are acids or bases.


Theory

  • Acids are sour in taste, Eg: vinegar  (Ethanoic acid) and lemons (Citric acid).

  • Alkalis are substances chemicals that react with acids and neutralize them. Eg: Soap and washing powder are alkaline.

Acids and alkalis are found in a number of substances, Some are edible and can be found in foods. Some are very strong and can be harmful, such as the acid used in car batteries and the alkali used in oven cleaners.


Apparatus Required

  • Water

  • Red cabbage leaves

  • Lemon juice

  • Vinegar

  • baking soda

  • Colanders

  • Detergent

  • Glass jars of the same size


Procedure

  • Cut the cabbage leaves into small pieces, boil a cup of water separately.

  • Place the cabbage pieces in a bowl and pour the water into the bowl. Keep it for several minutes so that the cabbage pieces get soaked.

  • Take glass jars and place them apart. Pour every chemical (lemon juice, vinegar, detergent, and soda) in each jar.

  • Now to determine whether the substance is a base or an acid pour the cabbage juice indicator into each jar. If the mixture turns pink or red the chemical is an acid and if it turns blue or green the chemical is a base.


The Red Cabbage pH Scale

Different red cabbage ph levels and the colours obtained during the red cabbage juice indicator are given below:

(Image to be added soon)

pH

2

4

6

8

10

12

Colour

Red

Purple

Violet

Blue

Green

Greenish-yellow


Did You Know?

Apart from the solution, pH paper strips can also be made using red cabbage. We can use filter paper and dip it in the concentrated solution obtained from red cabbage. Soak it for some time and then take the paper to dry it. Once it is dried, cut the paper into small strips and they are ready to be used. Pour a drop of liquid on the test strip and check the colour obtained. The strip also turns red or green depending on whether it is acidic or basic.


FAQs (Frequently Asked Questions)

1. What is the pH of red cabbage juice?

The pH of red cabbage is around 7. It contains a chemical called anthocyanin which changes colour depending on the acidity of its environment.

2. Is red cabbage a natural indicator?

Red cabbage juice contains a natural pH indicator that changes colours depending on the acidity of the solution. The pigment in red cabbage that causes the red colour change is called flavin.

3. How long can we keep the red cabbage indicator?

Unused red cabbage indicator solution can be stored in a stoppered flask and refrigerated for one week.