What is Henry’s law and Raoult’s law

Henry’s law

It states that partial pressure of the solute gas is proportional to a mole fraction of that component in liquid phase but proportionality constant is H

p_A = H* x_A=Y_A . P

       where

• p_A = equilibrium partial pressure of pure liquid 'A'
• H = Henry's law constant for A in specific solvents
• x_A= mole fraction of A in the liquid phase
• Y_A = mole fraction of A in the vapor phase
• P = equilibrium pressure
• Henry's law is valid when x_A is close to zero that is for a dilute solution of 'A'

Raoult’s law

It states that the equilibrium partial pressure of components 'A' is equal to the product of vapor pressure and mole fraction of 'A' in the liquid phase.

         Mathematically

p_A = P_A⁰* x_A=Y_A . P

      where

• P_A⁰ = vapor pressure of pure liquid A
• Raoult's law is valid when x_A is close to 1 that is when the liquid phase is almost pure

WHAT IS MOLALITY

Molality

Molality is defined as the mole of the solute dissolved in one kilogram of solute.

Example: -
A solution of caustic soda contains 20 % NaOH by weight of a solution. The density of the solution is 1.196kg/lit. Find the molality
Solution ⇒

Given: - 20 % NaOH in the caustic soda solution
Basis: - 100 kg of solution

Formula:-

As the Solution contains 20 % of NaOH

∴ Weight of NaOH = 100 * 0.2 = 20 kg.................(1)

Weight of water (solvent ) = 100 - 20 = 80 kg..............(2)

As we know