Question

Why concentrated sulphuric acid cannot be used for drying h2?

Answer 1

First of all it is not H2, it is H2S.

Hydrogen sulphide is a powerful reducing agent and concentrated sulphuric acid has significant oxidising power. The former can be oxidised to elemental sulphur when it comes in contact with the acid.

So, concentrated H2SO4 is not a suitable drying agent for H2S.