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WATER BECOMES PINK AND COLOURLESS AGAIN:
It is the best demonstration of pH indicator.
Definition of p indicator:
A pH indicator is a chemical compound added to a solution to know acidic /basic nature of the solution visually.
In this experiment, phenolphthalein is used as a pH indicator. It turns colourless in acidic solution and pink in basic solution.
Apparatus: Conical flask, straw, beaker
Chemicals: sodium carbonate solution phenolphthalein indicator
Procedure and observations:
1. Take about 50 ml water in a beaker
2. Add approximately 2-3 drops of phenolphthalein indicator in this water
3. Observe the colour of the solution: It is colourless
4. Add 3-4 drops the sodium carbonate solution to the bottom of empty conical flask
5. Add water containing Phenolphthalein indicator to this glass. Observe the colour of the solution. It turns to pink. It is due to Sodium carbonate present in the flask
6. How will you make it colourless again? Just use the straw and blow air for some time in this pink solution. It will become colourless.
When phenolphthalein comes in contact with Sodium carbonate, it became pink as sodium carbonate is a base. When we blow air in this solution Carbon dioxide in the air reacts with water to form Carbonic acid. Addition of carbonic acid makes the solution neutral and then acidic in nature and indicator turns colourless again
Chemical reaction: Co2 (g) H20 (l) —–x H2CO3 (aq)