Question

When 10 g nonvolatile urea is dissolved in H2O,
vapour pressure decreases by 10%. What will be
mole fraction of solvent?
(1) 0.1 (2) 0.8 (3) 0.9 (4) 0.09​

Answer 1

Answer :

When 10g non-volatile urea is dissolved in H₂O, vapour pressure decreased by 10%.

We have to find mole fraction of solvent$.$

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◈ Relative lowering of vapour pressure by raoult's law is given by,

• (P°- P)/P° = X₂

P° denotes initial vapour pressure

P denotes final vapour pressure

X₂ denotes mole fraction on solute

ATQ, vapour pressure of solution decreases by 10%.

➝ P = P° - 10% of P°

➝ P = P° - (10P°/100)

➝ P = 90P°/100

➝ P = 0.9P°

◈ Mole fraction of solvent :

⇒ (P°- P)/P° = (1 - X₁)

⇒ (P°- 0.9P°)/P° = 1 - X₁

⇒ 0.1 = 1 - X₁

⇒ X₁ = 0.9