Correct Answer: 3
Spin only magnetic moment 3.87 BM corresponds to three unpaired electrons, indicating Cr(III) with d3 configuration.
Given that the complex behaves as a 1 : 2 electrolyte, its structure must be:
[Cr(H2O)4Cl2]Cl·2H2O
This gives one chloride ion outside the coordination sphere.
Molar mass of the complex:
Cr = 52 Cl3 = 3 × 35.5 = 106.5 6H2O = 6 × 18 = 108
Total molar mass = 52 + 106.5 + 108 = 266.5 g mol−1
Moles of complex taken:
2.75 / 266.5 ≈ 0.0103 mol
When passed through cation exchanger, the complex cation is removed and free Cl− ions remain in solution.
Each mole of complex releases 3 moles of Cl− ions.
Total moles of Cl−:
0.0103 × 3 ≈ 0.0309 mol
These react with AgNO3 to form AgCl:
Ag+ + Cl− → AgCl(s)
Molar mass of AgCl:
AgCl = 108 + 35.5 = 143.5 g mol−1
Mass of AgCl formed:
0.0309 × 143.5 ≈ 4.43 g
Nearest integer value:
= 3 g
Hence, the required amount of AgCl is 3 g.
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