Question

On treating 100 rnL of 0.1 M aqueous solution of the complex CrCl₃.6H₂O with excess of AgNO₃,2.86 g of AgCl was obtained. The complex is :

• A. [Cr(H₂O)₃Cl₃].3H₂O
• B. [Cr(H₂O)₄Cl₂]Cl.2H₂O
• C. [Cr(H₂O)₅Cl]Cl₂.H₂O
• D. [Cr(H₂O)₆Cl₃]

Answer 1

The Correct Option is C

• The problem involves the complex CrCl₃·6H₂O, which when treated with excess AgNO₃, produces 2.86 g of AgCl. The reaction indicates the displacement of chloride ions from the complex by silver ions.
• The complex CrCl₃·6H₂O contains three chloride ions, but upon reaction with excess silver nitrate, two chloride ions are removed, and one chloride ion remains coordinated with the chromium ion in the complex.
• This results in a complex of the form [Cr(H₂O)₅Cl]Cl₂·H₂O, where chromium is coordinated to five water molecules and one chloride ion, and there are two free chloride ions and one water molecule as part of the structure.

Thus, the correct complex is [Cr(H₂O)₅Cl]Cl₂·H₂O, making option (C) the correct answer.

Answer 2

In this reaction, the amount of AgCl formed indicates how many chloride ions are present in the complex. The formation of 2.86 g of AgCl corresponds to a certain number of moles of chloride ions. Since each chloride ion from the complex reacts with Ag⁺ to form AgCl, the number of moles of AgCl will help determine the composition of the complex. Based on the mole calculations, the complex is determined to be [Cr(H₂O)₅Cl]Cl₂·H₂O.