Using Raoult’s law explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.
1. CHCl3(l) and CH2Cl2(l)
2. NaCl (s) and H2O (l)
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.
(a) CHCl3(l) and CH2Cl2(l) both are volatile components.
Hence, for a binary solution in which both components are volatile liquids, the total pressure will be
p = p1 + p2 =
= + (1 - x1) =
where, p = total vapour pressure p1 = partial vapour pressure of component1 p2 = partial vapour pressure of component 2
(b) NaCl (s) and H2O (l) both are non-volatile components.
Hence, for a solution containing non-volatile solute, the Raoult’s law is applicable only to vaporisable component and total vapour pressure can be written as
