The acidic and basic nature of the compounds can also be indicated by some natural as well as chemical substances. They are known as indicators.
i. There are many natural substances such as rose petals, turmeric, beet root, etc that can be used as indicators. They are called natural indicators.
ii. Some chemical substances such as phenolphthalein, methyl orange, eosin are synthetic indicators.
iii. Olfactory indicators: Substances whose odour changes in acidic or basic solution are called olfactory indicator. An olfactory indicator works on the principle that when an acid or base is added to it, then its odour cannot be detected. Examples: onion and clove extract.
iv. Universal indicators: Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.
v. Uses of indicators: The acidic or basic nature of a compound can be judged. It is used in agriculture to determine the pH of the soil.
