Question

Find number of chloride ions present outside the co-ordination sphere of the compound having general formula CrCl3. 6H2O which is grey-green in colour and of which 0.1 mole of compound in aqueous solution gives 0.2 mole ppt. of AgCl on addition of AgNO3 solution.

• A. 2
• B. 3
• C. 4
• D. 6

Answer 1

Answer: (A)

2

Answer 2

1. Determine the number of ionizable chloride ions:

The reaction between the compound and AgNO₃ results in the precipitation of AgCl from the chloride ions present outside the coordination sphere.

Given: Moles of compound = 0.1 mol Moles of AgCl precipitated = 0.2 mol

The stoichiometry of the precipitation reaction is: [Complex]Clₓ (aq) + xAgNO₃ (aq) → xAgCl (s) + Complexₓ (aq) Where 'x' is the number of chloride ions outside the coordination sphere.

From the given data, the mole ratio of AgCl to the compound is: Number of ionizable Cl⁻ ions (x) = Moles of AgCl / Moles of compound x = 0.2 mol / 0.1 mol x = 2

2. Relate to the compound's properties:

The general formula of the compound is CrCl₃.6H₂O. The fact that 2 chloride ions are outside the coordination sphere means the complex has the formula [Cr(H₂O)₅Cl]Cl₂.H₂O. This specific isomer of CrCl₃.6H₂O is known to be light green or grey-green in colour, which matches the description given in the question.

Therefore, there are 2 chloride ions present outside the coordination sphere.