How to Make pH Indicator?

red cabbage

pH paper is filter paper that is used as pH indicators. Technically, pH papers or litmus papers are made using water soluble dye from lichens. pH indicators are used for testing the acidity of liquids. You can buy litmus papers from your nearby chemical suppliers. But, how to make pH indicator at home? In this activity we will be making cabbage pH papers at home.

Try it yourself

You need:

  1. Red cabbage – 1
  2. Water
  3. Paper cards
  4. Knife
  5. Pot
  6. Glass bowl
  7. Sieve
  8. Scissors
  9. Heater
  10. Lemon juice
  11. Vinegar
  12. Flat paper surface

What next?

The experiment involves the usage of knife and so require an adult administration and necessary safety requirements.

Step 1: Slice the cabbage into thin slices and add them into the pot.

Step 2: Add water to cover the cabbage in the pot and boil it over the heater.

Step 3: Strain the boiled water using a sieve to the glass bowl and let the water cool. The water will have a deep violet color.

Step 4: Once cold, add paper cards to the water and let the cards soak.

Step 5: Allow the cards get dry. Once dry, your cabbage pH papers are ready. We will use these cabbage pH papers to test the acidity of liquids. Click here to see that experiment.

Step 6: Pour a few drops of cabbage juice on the flat paper surface. Pour a few more drops on another place on the same paper surface.

Step 7: Pour a drop of vinegar on one part of the cabbage juice on the flat paper surface. Observe the color changes, if there is any.

Step 8: Pour a drop of lemon juice on the other part of the cabbage juice on the flat paper surface. Observe the color changes, if there is any.

Note your observations.

Logic:

Cabbage juice (the red one) contains anthocyanin. Anthocyanin can be used as a pH indicator. Lemon juice and vinegar both are acids. If you try with baking soda, it would give a different result as baking soda is base. There are also alternatives to cabbage for making pH indicators. You can see about how to make pH indicator without red cabbage in our upcoming posts. 

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