Question

A salt, which is heated with conc. sulfuric acid​ gives violet vapours, is
A. Iodide
B. Nitrate
C. Sulphate
D. Bromide

Answer 1

Hint: Iodine gas is violet in colour. The sulphate of iodine on reaction with iodine salt concentrate sulfuric acid produces iodine gas.

Complete Step by Step Answer:
Concentrate sulfuric acid on reaction with iodine salt that is potassium iodide gives potassium bisulfate along with hydrogen iodide. This hydrogen iodide in reaction with concentrated sulfuric acid produces iodine gas which gives the violet colour along with water and sulphur dioxide gas.’

Thus the reaction is given as follows:
$KI+{{H}_{2}}S{{O}_{4}}\to KHS{{O}_{4}}+HI$
$2HI+{{H}_{2}}S{{O}_{4}}\to 2{{H}_{2}}O+{{I}_{2}}+SO{}_{2}$
Thus the correct option is A.

Additional Information: Iodine is a halogen element. It has the symbol of $I$. It generally exists as a gas. It has the colour of violet blue. Iodine is generally obtained from seaweed. Starch generally acts as an indicator in titration reactions to determine the end point of a titration. Iodine gas reacts with starch, an indicator gives blue colour.

Note: Sulfuric acid is a strong acid and a strong oxidising agent. Thus it reduces potassium iodide to iodine gas and itself oxidises.