Question

Describe a test (other than electrolysis) to prove that hydrochloric acid contains chlorine gas.

Answer 1

Test: Heat concentrated hydrochloric acid with a strong oxidizing agent like Manganese dioxide (MnO₂).

Observation: A greenish-yellow gas with a pungent, choking smell is evolved. When a moist starch-iodide paper is brought near it, the paper turns blue-black, proving the gas is Chlorine.

Equation: \[\ce{MnO2 + 4HCl -> MnCl2 + 2H2O + Cl2 ^}\]