Question

What is one method of qualitatively analyzing a given salt for presence of ammonia?

(a) Solution turns blue litmus red

(b) Heating the salt causing decrepitation

(c) Using a reagent to obtain dirty brown precipitate

(d) Addition of NaOH causing white gelatinous precipitate

I had been asked this question in examination.

This intriguing question originated from P-Block Elements in portion P-Block Elements of Chemistry – Class 12

Answer 1

The correct option is (c) Using a reagent to obtain dirty brown precipitate

For explanation I would say: Typically, Nessler’s reagent is used to test for ammonia. Nessler’s reagent is an alkaline solution of potassium tetraiodomercurate (II). When it combines with ammonia it gives dirty brown precipitate due to the formation of [OHg2.NH2]I. Another method is to add a strong base and heat the mixture. The gas given off is pungent and turns red litmus blue.