Question

Describe with chemical equations, what happens when K₂Cr₂O₇ reacts with sodium chloride in the presence of conc. H₂SO₄.

Answer 1

When potassium dichromate (K₂Cr₂O₇) reacts with sodium chloride (NaCl) in the presence of concentrated sulphuric acid (H₂SO₄), chlorine gas (Cl₂) is liberated. This is a redox reaction where \[\ce{Cr2O^{2-}_7}\] (from K₂Cr₂O₇) acts as an oxidising agent, converting Cl⁻ ions into Cl₂ gas.

\[\ce{K2Cr2O7 + 4NaCl + 6H2SO4 -> 2KHSO4 + 2Cr(SO4)3 + 4NaHSO4 + 3Cl2 + 3H2O}\]