Question

If ethanol and chloroform are present in a molar ratio of 2:3 then what is the vapor pressure at 20° C if vapor pressures of pure liquids are 5.95 kPa and 21.17 kPa, respectively?

Answer 1

Explanation :

Given :

P°e = 5.95 kPa

P°c = 21.17 kPa

Mole ratio of ethanol : chloroform : : 2 : 3

 

The mole fraction of ethanol, Xe = 2/5 = 0.4

Mole fraction of chloroform, Xc = 3/5 = 0.6

From Raoult’s law, P1 = P°1 × X1

Pe = 5.95 × 0.4 = 2.38 kPa

Pc = 21.17 × 0.6 = 12.702 kPa

From Dalton’s law, P (total) = Pe + Pc

P (total)= 2.38 + 12.702

              = 15.082 kPa.

The total vapour pressure is 15.08 KPa.