Question

Elevation in boiling point of $Ca{\left(N{O}_3\right)}_2$ gives molar mass as 131.2. The degree of dissociation of $Ca{\left(N{O}_3\right)}_2$ is:

• A. $100\%$
• B. $75\%$
• C. $50\%$
• D. $12.5\%$

Answer 1

The correct option is D $12.5\%$

$Ca{\left(N{O}_3\right)}_2\to {Ca}^{2+}+2N{O}_3^{-}$
Initial 1 0 0
At eq. $1-\alpha \alpha \alpha$

As we know, $i=1+2\alpha$

Calculated molecular weight of $Ca{\left(N{O}_3\right)}_2=164$

Observed molecular weight of $Ca{\left(N{O}_3\right)}_2=131.2$

$\therefore i=\frac{164}{131.2}=1+2\alpha$

$\therefore \alpha =0.125=12.5\%$