Question

What will be the molar mass of solute if vapour pressure of pure benzene is 450 mm Hg when 1.5 g of non-volatile solute is added to 30 g of benzene?
(Vapour pressure of solution= 400 mm Hg, Atomic mass C = 12, H = 1)

विकल्प

• 26.1 g mol^-1

• 30.0 g mol^-1

• 28.4 g mol^-1

• 35.1 g mol^-1

Answer 1

35.1 g mol^-1 

Explanation:

P⁰ = 450 mm Hg, P = 400 mm Hg, Mt = 78 g mol^-1 (molar mass of benzene),

W₁ = 30 g, W₂ = 1.5 g, M₂ = ?

`"M"_2 = ("W"_2"M"_1)/"W"_1 xx "P"_0/("P"_0 - "P")`

`therefore "M"_2 = (1.5 xx 78)/30 xx 450/(450 - 400)` = 35.1 g mol^-1