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Question

A, B and C are three complexes of chromium (III) with the emperical formula Cr(H2O)6Cl3. These complexes have either water or water and chloride ions as ligands. Complex A does not react with concentrated H2SO4, whereas complexes B and C loose 6.75% and 13.5% of their orignal mass respectively on treatment with conc. H2SO4.

A
B = [Cr(H2O)5Cl]Cl2.H2O
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B
C = [Cr(H2O)5Cl]Cl2.H2O
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C
The conductivity produced by complex B is more than that of complex C
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D
A, B and C are hydration isomers and produce 1, 2 and 3 moles of AgCl on reaction with AgNO3 respectively.
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Solution

The correct options are
A B = [Cr(H2O)5Cl]Cl2.H2O
C The conductivity produced by complex B is more than that of complex C
A = [Cr(H2O)6]Cl3
Cr(H2O)6Cl3 + H2SO4 No reaction
Because in it all H2O molecules are present in coordination sphere.

B = [Cr(H2O)5Cl]Cl2.H2O

[Cr(H2O)5Cl]Cl2.H2O + H2SO4 one molecule of H2O is removed
Because 1 H2O molecule is present outside the coordination sphere
Molecular weight of complex = 266.5
% loss = 18266.5×100=6.75%

C = [Cr(H2O)4Cl2]Cl.2H2O
[Cr(H2O)5Cl]Cl2.H2O + H2SO4 two molecules of H2O is removed
Because 2 H2O molecules are present outside the coordination sphere
Molecular weight of complex = 266.5
% loss = 18×2266.5×100=13.5%

[Cr(H2O)5Cl]Cl2.H2O [Cr(H2O)5Cl]2+(aq.) + 2Cl(aq.)
[Cr(H2O)4Cl2]Cl.2H2O [Cr(H2O)4Cl2]+(aq.) + Cl(aq.)
B produces 3 ions on dissociation and C produces 2 ions on dissociation and hence B has more conductivity.

A, B and C are hydration isomers because they have the same molecular formula but different number of H2O molecules inside and outside the coordination sphere.
Also, more the number of Cl ions outside the coordination sphere more the moles of AgCl is formed.

[Cr(H2O)6]Cl3 + AgNO3 3AgCl
[Cr(H2O)5Cl]Cl2.H2O + AgNO3 2AgCl
[Cr(H2O)4Cl2]Cl.2H2O + AgNO3 AgCl






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