question_answer 50)

    Which one of the following can be used as an acid-base indicator by a visually impared student?             (a) Litmus                                (b) Turmeric                       (c) Vanilla essence           (d) Petunia leaves              

Answer:

  (c) Vanilla essence is an olfactory indicator. So, its smell is different in acid and basic media which can be detected easily by a visually impared student. 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 characteristic smell of vanilla extract. An acidic solution like hydrochloric acid, however, does not destroy the smell of vanilla extract.