Choose the olfactory indicators and give their characteristics: red cabbage extract, onion, vanilla extract, litmus, clove oil.
Olfactory indicators: Onion, vanilla extract, clove.
Characteristics: An olfactory indicator works on the principle that when an acid or base is added, then its characteristic smell can be detected.
(i) Onion has a characteristic smell. When a base (like NaOH) is added to a cloth strip treated with onion extract—then the smell is destroyed. An acid solution (HCl) does not destroy the smell of onion.
(ii) Vanilla extract has a characteristic pleasant smell. If a basic solution like sodium hydroxide solution is added to vanilla extract, then we cannot detect the pleasant smell of vanilla. An acidic solution does not affect the smell of vanilla.
(iii) Similarly odour of clove oil is not affected in acidic solutions.
