Question
What are indicators? Name four acid-base indicators and mention their colour change.
Solution
Indicators are chemical substances which give different colours in acidic or basic solutions.
(i) Methyl orange gives pink colour with acid solution and yellow colour with base solution.
(ii) Phenolphthalein is colourless in acid solution while it turns into pink colour in base solution.
(iii) Litmus solution turns red in acid solution and blue in base solution.
(iv) Bromothymol blue is blue in base solution and is yellow in acid solution.
