Question

In the test for nitrogen, the sodium fusion extract is acidified with which of the following?

(a) Dilute sulphuric acid

(b) Dilute hydrochloric acid

(c) Concentrated hydrochloric acid

(d) Concentrated sulphuric acid

This question was posed to me during a job interview.

Enquiry is from Qualitative Analysis of Organic Compounds in section Organic Chemistry – Basic Principles and Technique of Chemistry – Class 11

Answer 1

Right answer is (d) Concentrated sulphuric acid

For explanation I would say: In the test for nitrogen, sodium cyanide first reacts with iron (III) sulphate and forms sodium hexacyanoferrate (II). On heating with concentrated sulphuric acid, some iron (II) ions are oxidized to iron (III)ions which react with sodium hexacyanoferrate (II) to produce iron (III) hexacyanoferrate (II), which is Prussian blue in color. Moreover, nitrogen atoms are soluble in concentrated sulphuric acid.