Question

What molality of nonvolatile solute is needed to lower the melting point of camphor by 1.010°c? (kf = 39.70ºc/m)?

Answer 1

Molality is defined as the ratio of moles of solute to the mass of solvent in Kg. It is also known as molal concentration.

Formula used for determining the molality is:

$\Delta T=K_{f}\times m$    (1)

where,

$\Delta T$ = change in temperature

$K_{f}$ = freezing point depression constant

m = molality

Here, $\Delta T$ =$1.010^{0}C$ and $K_{f}$ =$39.70^{0}C/m$

Put the above values in formula (1)

$1.010^{0}C=39.70^{0}C/m\times m$

$m=\frac{1.010^{0}C}{39.70^{0}C}$

= $0.0254 m$

Hence, molality of nonvolatile solute is $0.0254 m$