Question

In a Homogeneous mixture of A (Molar mass = 10) and B (Molar mass = 20), calculate the molality of solution if mole fraction of B is 0.6

Answer 1

Xb = 0.6

A = 10

B = 20

m = ?            

we know that

Xa + Xb =1

Xa = 1 - 0.6 = 0.94

m = xb /xa *1000/Ma

   = 0.6/0.94 * 1000/10

= 63.8

Answer 2

Given: Molar mass of A, M₁ = 10 g/mol

           Molar mass of B, M₂ = 20 g/mol

           Mole fraction of B, X₂ = 0.6

To Find: Molality of solution, m.

Solution:

To calculate m, the formula used:

• m = (X₂ x 1000) / X₁ x M₂
• here, X₁  is the mole fraction of A, which can be written as 1 - X₂
• ∴ m =  (X₂ x 1000) / (1 - X₂) x M₂

Applying the above formula:

m = (0.6 x 1000) / (1 - 0.6) x 20

   = 6 x 100 / (1-0.6) x 20

   = 3 x 10 / (1-0.6)

   = 30 / 0.4

   = 30 x10 / 4

   = 300 / 4

   = 75

Molality = 75m

Hence the molality of the solution is 75 molal.