Solutions and Colligative Properties 2 Question 8
8. $\mathrm{K}{2} \mathrm{HgI}{4}$ is $40 %$ ionised in aqueous solution. The value of its van’t Hoff factor $(i)$ is
(2019 Main, 11 Jan II)
(a) 1.6
(b) 1.8
(c) 2.2
(d) 2.0
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Solution:
- The ionisation of $\mathrm{K}{2} \mathrm{HgI}{4}$ in aqueous solution is as follows:
$$ \mathrm{K}{2}\left[\mathrm{HgI}{4}\right] \rightleftharpoons 2 \mathrm{~K}^{+}+\left[\mathrm{HgI}_{4}\right]^{2-} $$
van’t Hoff factor (i) for ionisation reaction is given as, $i=1+\alpha(n-1)$
where,
$n=$ number of ions,
$\alpha=$ degree of ionisation or dissociation
From above equation, it is clear that $n=3$
$$ \begin{aligned} i & =1+0.4(3-1) \ & \quad[\text { Given, } % \alpha=40 % \text { or } \alpha=0.4] \ & =1.8 \end{aligned} $$
