Question

Using Raoult's law explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.
(a) $CHC{l}_3\left(l\right)andC{H}_{2}C{l}_2\left(l\right)$

Using Raoult's law explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.
(b) $NaCl\left(s\right)and{H}_{2}O\left(l\right)$

Answer 1

According to Raoult's law for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction.
$p_1=p_1^{\circ }{x}_1$
(a) $CHC{l}_3\left(l\right)andC{H}_{2}C{l}_2\left(l\right)$ both are volatile components.
Hence, for a binary solution in which both components are volatile liquids, the total pressure will be $p=p_1+p_2=x_1{p}_1^{\circ }+x_2{p}_2^{\circ }=x_1{p}_1^{\circ }+(1-x_1)p_2^{\circ }=(p_1^{\circ }-p_2^{\circ })x_1+p_2^{\circ }$
where, p = total vapour pressure
$p_1$= partial vapour pressure of component 1
$p_2$= partial vapour pressure of component 2

(b) $NaCl\left(s\right)$ is non-volatile component.
Hence, for a solution containing non-volatile solute, the Raoult's law is applicable only to vaporisable component and total vapour presure can be written as
$p=p_1=x_1{p}_1^{\circ }$ : $p_{1}isthepartialpressureof{H}_{2}O$