Question

A solution containing 0.85g of $ZnC{l}_2$ in 125.0 g of water freezes at $-{0.23}^{0}C$. The apparent degree of dissociation of the salt is:
($k_f$ for water$=1.86\text{K kg mol^{-1}}$, atomic mass ; $Zn=65.3$ and $Cl=35.5$)

• A. $1.36\%$
• B. $2.47\%$
• C. $73.5\%$
• D. $7.35\%$

Answer 1

The correct option is C $73.5\%$

molar mass of $2nC{l}_2=136.3$

$moles=0.85/136.3$

$=0.00623$

$molarity=0.05m$

$△T_f=1.86\times 0.05$

$=0.09227$

$i=0.23/0.0927$

$=2.48$

$ZnC{l}_2\leftrightharpoons 2n^{2l}+2C{l}^{-}$

$a$ $0$ $0$

$a-a\alpha$ $a\alpha$ $2\alpha$

total moles of equations $=a(1+2\alpha )$

$i=2.48=1+2\alpha$

$\alpha -0.735$

$\%=73.5\%$