Question

Why is sulphuric acid used in the preparation of hydrogen gasin a laboratory?

Answer 1

Dilute sulfuric acid will react to produce hydrogen gas. Increasing the concentration will increase the rate of reaction. Since the product is in another phase (hydrogen is a gas) too rapid a reaction brings a risk of overpressurization and explosion. (This was once an issue with car batteries). Also rapid generation of hydrogen bubbles could splash concentrated acid onto onlookers or sensitive equipment.