Making Indicators

Aim: To make acid-base indicators using everyday substances. 

Equipment: Red cabbage, tea, beetroot, turmeric, cranberry juice, beaker, 100ml hot water, tripod, Bunsen burner, gauze mat, 1.0 moI L -1 HCI and 1.0 moI L -1 Na-OH. 

(We don't have Bunsen burners in the science room so we boiled hot water.)

Method: 

For Cabbage and Beetroot - Chop the cabbage into small pieces until you have enough to fill 2 cups. Place the cabbage in a large beaker and add water to cover the cabbage. Boil over a Bunsen burner for at least ten minutes for the colour to leach out of the cabbage. Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is about pH 7. (The exact colour you get depends on the pH of the water.) Place in a small beaker and leave to the side. Repeat this method for beetroot. 

For the tea - Put 100 ml of water in a beaker and boil. Turn off the Bunsen burner and put three bags in the beaker. Remove tea bags when the tea is very strong. Place in a small beaker and leave to the side. 

For the cranberry juice - Pour into a beaker and leave to one side. 

For the turmeric - Mix 1 teaspoon turmeric in 100 ml cup of alcohol, place in beaker and leave to the side. 

Task Two:

1. You now have five beakers, each containing a different indicator. 

2. Using a pipette, place 5 ml of the cabbage indicator into two test tubes. 

3. Add 5 ml of HCI (acid) to one test tube and 5 ml of NaOH (alkali) to the other test tube. 

4. Record the colour change on the table below. 

5. Clean the test tubes and repeat for beetroot, tea, cranberry and turmeric indicators. 

Results: