Question

The vapor pressure of water is $12.3KPa$ at $300K$. Calculate the vapor pressure of $1$ molal solution of a non-volatile solute in it.

Answer 1

$P_{H_{2}O}=P_A=12.3KPascal$

Let moles of solute be $1$
and mass of water be $1000g=1kg$

Number of moles of water $=\frac{1000}{18}=55.5moles$

According to Raoult's law of
vapor pressure of solute

$\Rightarrow P_{solute}={\chi }_{solute}\times P_{solute/total}$

$P_{solute}=\frac{1}{56.5}\times 12300Pascal$

$=217.7Pascal$