Question

A white substance A reacts with dilute H₂SO₄ to produce a colourless gas B and a colourless solution C. The reaction between B and acidified K₂Cr₂O₇ solution produces a green solution and a slightly coloured precipitate D. The substance D bums in air to produce a gas E which reacts with B to yield D and a colourless liquid. Anhydrous copper sulphate is turned blue on addition of this colourless liquid. Addition of aqueous NH₃ or NaOH to C produces first a precipitate, which dissolves in the excess of the respective reagent to produce a clear solution in each case. Identify. A , B, C, D and E. write the equations of the reactions involved.

Answer 1

Since the white substance A gives a colourless gas B with dil. H₂SO₄. Such gas may be H₂S gas. So substance 'A' may be metal sulphide (Na/K/Zn etc.)

When H₂S gas reacts with acidified K₂Cr₂O₇, solution, it gives green coloured solution of Cr₂(SO₄)₃ alongwith slightly yellow coloured ppt. of D as sulphur.

Sulphur on burning in oxygen to give SO₂ (E)