Question

What will be the elevation in boiling point for $13.44g$ of $CuC{l}_2$ dissolved in $1kg$ of water as solvent if $CuC{l}_2$ is fully ionised?
($K_b=0.52Kkgmo{l}^{-1}$
Molar mass of $CuC{l}_2=134.4g/mol$)

• A. 0.05
• B. 0.10
• C. 0.16
• D. 0.20

Answer 1

The correct option is C 0.16

Given,
$CuC{l}_2$ is an electrolytic solute and it is fully ionised
$\therefore$
$CuC{l}_2\to C{u}^{2+}+2C{l}^{-}$
Thus, the number of ions in the solution is 3
$\therefore$ i = 3, assuming complete ionization of $CuC{l}_2$
We know,
Corrected boiling point elevation of solution is,
$△T_b=i\times K_b\times m$
where,
$△T_b$ is the elevation in boiling point.
$K_b$ is molal elevation constant.
m is molality of solution.
i is van't Hoff factor
$\therefore$
$△T_b=i\times K_b\times \frac{w_B\times 1000}{m_B\times w_A}$
where,
$w_B$ is mass of solute
$m_B$ is molar mass of solute
$w_A$ is mass of solvent
$△T_b=3\times 0.52\times \frac{13.44\times 1000}{134.4\times 1000}=0.156\approx 0.16K$