Question

How will you distinguish between dilute H₂SO₄ and conc. H₂SO₄ ?

Answer 1

Difference between dilute H₂SO₄ and Conc. H₂SO₄ :

S.NO.	Dilute Sulphuric acid	Concentrated sulphuric acid
1	Barium chloride test : Barium chloride is added to dilute sulphuric acid white ppt.s of barium sulphate is formed. The precipitate is insoluble in dil.hydrochlroic acid or nitric acid. \[\ce{BaCl2 + H2SO4 -> BaSO4 v + 2HCl}\]	Addition to copper : Conc. sulphuric acid is added to copper and heated. Sulphur dioxide, which is colourless gas with the smell of burnt sulphur is evolved. \[\ce{Cu + 2H2SO4 -> CuSO4 + 2H2O + SO2}\] SO2 gas turns K2Cr2O7 paper green.
2	Lead nitrate test : Lead nitrate is added to dil. sulphuric is acid. White ppt. of lead sulphate is formed. The ppt. is insoluble in dil. Hydrochloric acid or nitric acid. \[\ce{Pb(NO3)2 + H2SO4 -> PbSO4 v + 2HNO3}\]	Addition of common salt : Common salt is added to conc. sulphuric acid. Hydrogen chloride a colourless pungent smelling acidic gas is evolved. Dense white fumes are seen if a rod dipped in ammonia solution is brought near it. \[\ce{NaCl + H2SO4 -> NaHSO4 + HCl}\]