Transition elements

Question

The elevation of boiling point of 0.10 M aqueous CrCl_{3}.x NH_{3} solution is two times that of 0.05 M aqueous CaCl_{2} solution. The value of x is _____.

[assume 100% ionisation of the complex and CaCl_{2}, coordination number of Cr as 6, and that all NH_{3} molecules are present inside the coordination sphere)

Moderate

Solution

For 0.05 M CaCl_{2}, i = 3

Effective molarity of CaCl_{2} = 0.05 × 3 = 0.15

effective molarity of complex = 2 × effective molarity of CaCl_{2}

= 2 × 0.15 = 0.3 M

So the complex is producing 3 ions on dissociation, which is possible only when, the value of x = 5.

$\left[CrCl{\left(N{H}_{3}\right)}_{5}\right]{\mathrm{Cl}}_{2}\rightleftharpoons [\mathrm{Cr}\mathrm{Cl}{\left({\mathrm{NH}}_{3}\right)}_{5}{]}^{2+}+2{\mathrm{Cl}}^{-}$

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