When potassium dichromate is heated with any chloride salt in the presence of Conc. H2SO4, orange-red vapours of chromyl chloride (CrO2Cl2) is evolved. This reaction is used to confirm the presence of chloride ions in inorganic qualitative analysis.
The chromyl chloride vapours are dissolved in sodium hydroxide solution and then acidified with acetic acid and treated with lead acetate. A yellow precipitate of lead chromate is obtained.