Relative lowering of vapor pressure produced by dissolving 71.5g of a substance in 1Kg of water is 0.0073. Molecular weight of substance will bea)18b)342c)60d)180Correct answer is option 'D'. Can you explain this answer?

Question

Answer

Relative lowering of vapor pressure:

The relative lowering of vapor pressure is given by the formula:

ΔP/P₀ = x₂M₁/x₁M₂

where ΔP is the lowering of vapor pressure, P₀ is the vapor pressure of the solvent (pure water), x₂ is the mole fraction of the solute, M₁ is the molar mass of the solvent (water), x₁ is the mole fraction of the solvent, and M₂ is the molar mass of the solute.

Given:

ΔP/P₀ = 0.0073

x₂ = mass of solute/mass of solution = 71.5g/(71.5g + 1000g) = 0.066

x₁ = 1 - x₂ = 0.934

M₁ = 18 g/mol (molar mass of water)

Substituting these values in the above formula, we get:

0.0073 = (0.066 x 18)/(0.934 x M₂)

Solving for M₂, we get:

M₂ = (0.066 x 18)/(0.934 x 0.0073) = 180 g/mol

Therefore, the molecular weight of the substance is 180 g/mol, and the correct option is D.

Answer

D 180

Answer

D

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