Question

Compound A is a light green crystalline solid. it gives the following tests 

(i) It dissolves in dilute sulphuric acid. No gas is produced. 

(ii) A drop of KMnO₄ is added to the above solution. The pink colour disappears. 

(iii) Compound A is heated strongly. Gases B and C, with pungent smell. come out. A brown residue D is left behind. 

(iv) The gas mixture (B and C) is passed into a dichromate solution. The solution turns green, 

(v) The green solution from step (iv) gives a white precipitate E with a solution of barium nitrate, 

(vi) Residue D from step (iii) is heated on charcoal in a reducing flame. It gives a magnetic substance. 

Name the compound A, B, C, D and E.

Answer 1

Compound 'A' is a light green crystalline solid, so it may be ferrous sulphate. 

(i) FeSO₄ is a salt of strong acid and weak base, so it hydrolysed in dil H₂SO₄ but no gas is produced. 

(ii) Ferrous sulphate is a strong reducing agent, thus decolourises the KMnO₄ solution.

(iii) Ferrous sulphate on strong heating gives both SO₂ 'B' and SO₃ 'C' alongwith a residue of Fe₂O₃ 'D'.

(iv) This gaseous mixture reduced dichromate to green solution and also give sulphuric acid in the solution.

(v) This sulphuric acid (formed in step (iv)) gives white ppt. with a solution of Ba(NO₃)₂ due to formation of BaSO₄ 'E'.

(vi) The residue 'D' when heated on charcoal in a reducing flame, reduces to iron (Fe) which is a magnetic substance. 

Hence, A, B, C, D and E are respectively FeSO₄, SO₂, SO₃,Fe₂O₃ and BaSO₄.