(a) Explain the following:

(i) Henry’s law about the dissolution of a gas in a liquid.

(ii) Boiling point elevation constant for a solvent.

(b) A solution of glycerol (C₃H₈O₃) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42°C. What mass if glycerol was dissolved to make this solution? (K_b for water = 0.512 K kg mol^-1)

(a)

(i) Henry’s law states that partial pressure of a gas in the vapour phase is proportional to the mole fraction of the gas in the solution. If p is the partial pressure of the gas in the vapour phase and x is the mole fraction of the gas, then Henry’s law can be expressed as:

p = K_Hx

Where,

K_H is Henry’s law constant

(ii) The boiling point elevation constant or molal elevation constant is a constant quantity for a solute which is related to molar mass and elevation in boiling point by the following relation.

Where, K_b is the boiling point elevation constant

M_B is the molar mass of the solute

W_B is the weight of the solute

W_A is the weight of the solvent

T_b is the elevation in boiling point

(b) W_B =?

W_A = 500g

K_b = 0.512 Kkg mol^-1

T_b = 100.42°C - 100°C

= 0.42°C

M_B = 3 x 12 + 8 x 1 + 3 x 16

= 36 + 8 + 48 = 92