A, B and C are three complexes of chromium (III) with the empirical formula H 12 O 6 Cl 3 Cr. All the three complexes have water and chloride ion as ligands. Complex A does not react with concentrated H 2 SO 4, whereas complexes B and C lose 6.75 % and 13.5 % of their original mass, respectively, on treatment with concentrated H 2 SO 4. Identify A, B and C.

Question

A, B and C are three complexes of chromium (III) with the empirical formula H 12 O 6 Cl 3 Cr. All the three complexes have water and chloride ion as ligands. Complex A does not react with concentrated H 2 SO 4, whereas complexes B and C lose 6.75 % and 13.5 % of their original mass, respectively, on treatment with concentrated H 2 SO 4. Identify A, B and C. (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

A has no water molecules of crystallisation.
Hence,

A

is

[C r (H_{2} O_{6}] C l_{3}

.
Both

B

and

C

loses weight with concentrated

H_{2} S O_{4}

, therefore, both

B

and

C

have some water molecules of crystallisation.
Moreover, weight loss with

C

is just double of the same with

B

indicates that number of water molecules of crystallisation of

C

is double of the same for

B

. Therefore,

B

has one and

C

has two water molecules of crystallisation.

B = [C r (H_{2} O)_{5} Cl] C l_{2} \cdot H_{2} O, C = [C r (H_{2} O)_{4} C l_{2}] Cl \cdot 2 H_{2} O