Question

State Raoult’s law for solutions containing volatile solutes.

State and explain Raoult’s law for solutions containing volatile liquids.

Answer 1

For a solution of volatile liquids, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction.

If p_i is the partial vapour pressure of i^th component in a solution and χ_i is its mole fraction in the solution, then according to Raoult’s law,

p_i ∝ χ_i

or p_i = constant × χ_i    ...(i)

If we consider the component in its pure state, then 

`p_i = p_i^circ` and

χ_i = 1

Where P_i is the vapour pressure of the i^th component in the pure state. In the case of the pure i^th component, we shall have a 100% pure component, and χ_i will be equal to 1. Substituting the values in Eq. (i), we have

p_i = constant × 1

or constant = `p_i^circ`

Again putting the value of the constant in Eq. (i), we have

`p_i = p_i^circ* chi_i`