Question

PtCl₄ . 6H₂O can exist as a hydrated complex. One molal aqueous solution of the salt recorded a depression in freezing point of 3.72°C. If the salt is assumed to be 100% ionised in solution and K_f for H₂O is 1.86 K kg mo1⁻¹, the molecular formula of the complex is likely to be ______.

Options

• [Pt(H₂O)₆)]Cl₄

• [Pt(H₂O)₄Cl₂]Cl₂ . 2H₂O

• [Pt(H₂O)₃Cl₃]Cl . 3H₂O

• [Pt(H₂O)₂Cl₄]Cl . 4H₂O

Answer 1

PtCl₄.6H₂O can exist as a hydrated complex. One molal aqueous solution of the salt recorded a depression in freezing point of 3.72°C. If the salt is assumed to be 100% ionised in solution and K_f for H₂O is 1.86 K kg mo1⁻¹, the molecular formula of the complex is likely to be [Pt(H₂O)₃Cl₃]Cl . 3H₂O.

Explanation:

Given: The salt is PtCl₄ . 6H₂O.

The solution is a 1 molal aqueous solution.

The depression in freezing point is

ΔT_f = 3.72°C

The salt is assumed to be 100% ionised.

The cryoscopic constant for water is K_f = 1.86 K kg mo1⁻¹

We know that

ΔT_f = i K_f m

`i = (Delta T_f)/(K_f * m)`

`i = 3.72/(1.86 xx 1)`

i = 2

For [Pt(H₂O)₃Cl₃]Cl . 3H₂O, i = 1 + 1(Cl⁻) = 2