The substances that show different colours in different mediums or the substances that are used to distinguish between an acid and base are called indicators.
1. Natural Indicators: The indicators obtained from plants are called natural indicators.
2. Synthetic Indicators: These indicators are manufactured in laboratories.
(a) Methyl Orange
3. Olfactory Indicators: These indicators change their smell when dipped in acid and base.
(a) Onion Extracts
(b) Vanilla Extracts
Ques. What is an indicator?
Ans. An indicator is a dye that changes colour when it is put into an acid or a base. An indicator tells us whether a given substance is an acid or a base by change in its colour.
Ques. What is a universal indicator?
Ans. Universal indicator is a solution, which undergoes several colour, changes over a wide range of pH. The colour is used to ‘indicate’ pH directly. Universal indicators are usually mixtures of several indicators.
Ques. Name the common indicators used to test acid, bases and salts?
Ans. The three common indicators to test for acids and bases are
Ques.What are olfactory indicators. Give examples?
Ans. Those substances whose smell or odour changes in acidic or basic solution are called olfactory indicators.
Example: Onion and Vanilla extract
Ques. What is the colour of Phenolphthalein in acidic and basic medium?
Ans. It remains colourless in acids and turns pink in basic medium.