Raoult’s Law Chemistry Notes
Raoult’s Law :
First of all, French chemist F.M. Raoult (1886), established relationship between lowering of vapour pressure and concentration of solution.
Raoult’s Law for a solution containing volatile solute :
→ The partial vapour pressure of a volatile component present in solution at a certain temperature is equal to product of vapour pressure of that component in pure state and mole fraction of that component.
→ Suppose two volatile components A and B are present in solution. Partial pressures in that solution are PA and PB respectively. Their vapour pressures in pure state are p°A and p°B respectively. Their mole fractions are xA and xB respectively then, Mole fraction of component A
Raoult’s Law for a solution containing non volatile Solute :
The vapour pressure of solution having non-volatile solute (B) is equal to partial vapour pressure of volatile solvent (A) only because the partial vapour pressure of non-volatile solute is negligible. So, Vapour pressure of solution
Hence, according to Raoult’s law.” The relative lowering of vapour pressure for a solution having non-volatile solute at a certain temperature is equal to mole fraction of solute.”