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A certain inorganic compound (A) on heating loses its water of crystallization. On further heating, a blackish brown powder (B) and two oxides of sulphur (C and D) are obtained. The powder (B) on boiling with hydrochloric acid gives a yellow solution (E). When H 2 S is passed in (E) a white turbidity (F) and an apple green solution (G) are obtained. The solution (E) on treatment with thiocyanate ions gives a blood red coloured compound (H). Identify compounds from (A) to (H).

A certain inorganic compound (A) on heating loses its water of crystallization. On further heating, a blackish brown powder (B) and two oxides of sulphur (C and D) are obtained. The powder (B) on boiling with hydrochloric acid gives a yellow solution (E). When H2S is passed in (E) a white turbidity (F) and an apple green solution (G) are obtained. The solution (E) on treatment with thiocyanate ions gives a blood red coloured compound (H). Identify compounds from (A) to (H).

Grade:11

1 Answers

Aditi Chauhan
askIITians Faculty 396 Points
9 years ago
(i) Since the compound (A) on strong heating gives two oxides of sulphur (C and D) which might be SO2 and SO3, it must be a sulphate.
(ii) The reaction of compound (E) with thiocyanate to give blood red coloured compound (H) indicates that (E) must have Fe3+ ion.
Thus the compound (A) must be ferrous sulphate FeSO4. 7H2O, which explain all given reactions as below (Fe2+ ion of FeSO4 is changed to Fe3+ during heating).
FeSO4 7H2o \overset{heat}{\rightarrow}FeSO4 + 7H2O↑
Ferrous sulphate Ferrous
Sulphate
2 FeSO4 \overset{heat}{\rightarrow}Fe2O3 + SO2 + SO3
Ferrous Ferric (C)2 (D)3
Sulphate oxide,
(Blackish
Brown powder)
(B)
Fe2O3 + 6 HCI → 2FeCI3 + 3H2O
(B) Ferric chloride
(Yellow solution). (E)
2FeCI3 + H2S → 2FeCI2 + 2HCI + S
(E) Apple white
green (G) turbidity (F)
FeCI3 + 3NH4CNS → Fe (CNS)3 + Nh4CI
(E) Ferric thiocyanate
(blood red colour)

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