Question

A solution of an organic compound is prepared by dissolving 34.2g in 500g of water. Calculate the molar mass of the compound and freezing point of the solution. Given that Kb for water=0.52k/mol,boiling point of solution=100.104°c.Kf(water)=1.87k/mol.

Answer 1

Given:

w = 34.2 gm

W = 500 gm

Kb = 0.52 K/mol

B.P. = 100.104 °C

Kf = 1.87

To Find:

Molar Mass of compound and freezing point of the solution.

Calculation:

- We know that B.P. of water = 100 °C

⇒ Elevation in B.P, ΔTb = 100.104 - 100 = 0.104 °C

- Again, we know that

ΔTb = Kb × m

⇒ 0.104 = 0.52 × (34.2 × 1000)/ M.wt × 500

⇒ M.wt = 35.568 / 0.104

⇒ M.wt = 342 gm

- We know that

ΔTf = Kf × m

⇒ 0 - Tf = 1.87 × (34.2 × 1000)/ 342 × 500

⇒ Tf = - 0.374 °C

- So the molecular weight of compound is 342 gm and the freezing point of the solution is -0.374 °C