Using Raoult's law, explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions : (i) `CHCl_3 (l) " and " CH_2Cl_2(l)` (ii) `NaCl (s) " and " H_2O (l)`

Explanation

(i) For a binary solution having both components as volatile liquids, the total pressure will be
`p = x_1p_1^0 + x_2p_2^0`
`= x_1p_1^0 + (1-x)p_2^0`
`= (p_1^0 - p_2^0) x_1 + p_2^0`
p = total vapour pressure
`p_1` = partial vapour pressure of component 1 (say `CHCl_3`)
` P_2` = partial vapour pressure of component 2 (say `CH_2Cl_2`)
`x_2` = mole fraction of `CHCl_3`
(ii) For a solution containing non-volatile solute, the Raoult.s law is applicable only to vaporisable component (1) and total vapour pressure is written as
`p = x_1p_1^0`