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ChemistryNumerical+3Question 30 of 54

JEE Advanced 2019 · Paper 2, Chemistry question 12

The mole fraction of urea in an aqueous urea solution containing 900 g of water is 0.05. If the density of the solution is 1.2 g cm⁻³, the molarity of urea solution is ______

(Given data: Molar masses of urea and water are 60 g mol⁻¹ and 18 g mol⁻¹, respectively)

Answer and worked solution

Official answer: 2.8

Moles. 900 g of water is 50 mol. With xurea=0.05x_{urea}=0.05,
nn+50=0.05  ⟹  n=2.63 mol (158 g).\frac n{n+50}=0.05\implies n=2.63\text{ mol}\ (158\text{ g}).

Volume. The solution's mass is 10581058 g, so its volume is 10581.2=882\dfrac{1058}{1.2}=882 mL.

Molarity.
M=2.630.882=2.98 M.M=\frac{2.63}{0.882}=2.98\text{ M}.
Answer: 2.98 (key: 2.80 to 3.05)

Topics:Concentration termsConcentration and solubility
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