Reaction of concentrated sulphuric acid and sodium chloride

Question

2004 CE Chemistry Paper 1 Q2a:

Suggest a chemical test to distinguish table salt (sodium chloride) and white sugar (sucrose).

Here is what the suggested answer says:

"Treat the substances with concentrated sulphuric acid. White sugar turns black, while table salt gives misty fumes."

My question is: What is the "misty fumes" as mentioned in the suggested answer? How is it formed? (Chemical equations are always welcome.)

Answer 1

The misty fumes are hydrogen chloride gas. Sodium chloride reacts with concentrated sulphuric acid to give hydrogen chloride gas.
NaCl + H2SO4 → NaHSO4 + HCl
Note that one of the products is NaHCO3, but not Na2CO3.

Although hydrogen chloride is a colourless gas, it usually appears as white fumes in air. This is because hydrogen chloride gas is very soluble in water, and thus hydrogen chloride absorbs moisture in air readily to give small solution droplets of hydrochloric acid, and the small droplets in air appear as white fumes.