Question

Boojho, paheli and their friend Golu were provided with a test tube each containing china rose solution which was in colour. Boojho added two drops of the solution ‘A’ in his test tube and got a dark colour. Paheli added 2 drops of solution ‘B’ to her test tube and got green colour. Golu added 2 drops of solution ‘C’ but could not get any change in colour. Suggest the possible cause for the variation in the results.

Answer 1

Indicators:

• Indicators are chemical compounds that change the colour of a substance to indicate whether it is basic or acidic. Indicators change colour when added to either an acidic or basic solution, and the colour shift for acids and bases is distinct.
• Thus, the indicator aids us in determining if a particular solution is basic or acidic in nature.
• Indicators derived from plants are referred to as natural indicators.
• Examples: Turmeric compound is an acid-base indicator; when acid or neutral solutions are added, the colour will remain as yellow. If sodium hydroxide, is added to it, it gives a pinkish colour.
• China rose changes the colour of acidic solutions to dark pink, basic solutions to a greenish colour, and neutral solutions remain colourless.

Observation of colour change:

• Solution A is acidic since it changes the colour of China rose to a dark pink hue. Solution B is a basic solution because it changes the colour of China rose to green. Solution C is a neutral solution because it did not alter the colour of the china rose solution.