On adding concentrated H2SO4 to a salt, if a colourless gas with pungent smell is evolved, Cl– may be present.
MCl + H2SO4 → MHSO4 + HCl (Hydrogen Chloride, colourless gas)
Silver Nitrate Test
A curdy white precipitate insoluble in conc. HNO3 is obtained on adding silver nitrate to water solution. Acidify with dil HNO3 before adding AgNO3 in case sodium carbonate extract in used.
Ag+ + Cl– → AgCl ↓
Curdy white precipitate is soluble in ammonium hydroxide.
AgCl + 2NH4OH → [Ag(NH3)2]+ + 2H2O (Diammine silver chloride, colourless)
Chromyl Chloride Test
Yellow fumes of Chromyl Chlorides are obtained on heating a mixture of salt and solid K2Cr2O7 and concentrated H2SO4 in a dry test tube.
2MCl2 + K2Cr2O7 + 3H2SO4 → 2MSO4 + K2SO4 + 2CrO2Cl2 (Chromyl chloride, Orange red)
Chromyl chloride fumes turns dilute NaOH yellow
CrO2Cl2 + NaOH → Na2CrO4 (Sodium chromate, yellow)
A yellow precipitate of lead chromate, PbCrO4 is formed on adding lead acetate to the yellow solution acidified with CH3COOH
Na2CrO4 + Pb(CH3COO)2 → PbCrO4 (lead chromate, yellow precipitate)