Question

Which one of the following can be used as an acid-base indicator by a visually impaired student? Justify your answer.
(a) Litmus
(b) Turmeric
(c) Vanilla essence
(d) Phenolphthalein

Answer 1

Vanilla essence is an olfactory indicator and it has a characteristic pleasant odour. If vanilla extract is added to a basic solution, the characteristic odour of vanilla extract is lost. On the other hand, an acidic solution, does not destroy the odour of vanilla extract.
So, an olfactory indicator exhibiting such behaviour (different odours) in different medium can be used by a visually impaired student. Hence, option (c) is the correct answer.