1. MAKING A pH INDICATOR
INTRODUCTION
A pH indicator is a substance which has one colour when added to
an acidic solution and a different colour when added to an alkaline
solution. By determining the pH of a solution we can tell if the
solution is harmful to the environment.
PROBLEM OR QUESTION
What would be the colour change of an acidic solution?
What would be the colour change of an alkaline solution?
Can we use any other fruit or vegetable to measure pH?
HYPOTHESIS
We think that the colour change is not going to be very significant if
we just use red cabbage. Maybe, we need to add something else to
see a colour change.
MATERIALS
Each working group will require:
• Beaker (250 cm3)
• Bunsen burner
• Tripod
• Gauze
• Heat resistant mat
• Test-tubes, 3 (see note 1)
• Test-tube rack
• Dropping pipette
• Several pieces of red cabbage or beetroot
• Dilute hydrochloric acid, 0.01 mol dm-3 (Low hazard at this
concentration)
• Sodium hydroxide solution 0.01 mol dm-3 (Low hazard at this
concentration)

2. • De-ionised or distilled water
PROCEDURE
SAFETY: Wear eye protection throughout. Consider clamping the
beaker.
a. Boil about 50 cm3 of water in a beaker.
b. Add 3 or 4 small (5 cm) pieces of red cabbage to the
boiling water.
c. Continue to boil the red cabbage in the water for about 5
minutes. The water should turn blue or green.
d. Turn off the Bunsen burner and allow the beaker to cool for
about 15 minutes.
e. Place 3 test-tubes in a test-tube rack. Half-fill one of the
test-tubes with acid, one with alkali, and one with distilled or
de-ionised water. Label the test-tubes.
f. Use a dropper pipette to add a few drops of the cabbage
solution to each test-tube. Note the colour of the cabbage
solution in each of the three test-tubes.

3. OBSERVATIONS
After the cooling process we added about 5 cc of each solution into
each of the three test tubes using separate pipettes. To each test
tube, we added about 3 cc of the red cabbage solution. The colour
change was immediate. The first test tube with the acid solution
turned bright yellow. The second test tube with the alkaline solution
turned pink. The third test tube with distilled water turned light
purple, just like the red cabbage solution.
Test tube 1 Test tube 2
Test tube 3
Acid solution Alkaline solution
Neutral solution
CONCLUSION
The experiment was very simple and easy to understand. It worked!
The solution did change colour with the red cabbage solution that
was added. This is an easy way to determine if a particular solution
is acidic or alkaline. We can use this experiment to test for acid rain,
to test the drinking water, or the water that comes from the faucet.
Also, if the water in a river or a lake is acidic we can conclude that
there has been acid rain or that it has been contaminated from
something in the soil. Knowing if a natural solution is too acidic, it
will let us know if the animals in the area are in danger.

4. It would be interesting to know if other natural products can be used
as pH indicators, besides red cabbage and beetroot.