Question

If the mass percentage of urea in an aqueous
solution is 15% then molality of urea in the solution
is (molar mass of urea = 60 g mol-)
(1) 2.94 m
(2) 5.62 m
(3) 4.25 m
(4) 3.21 m​

Answer 1

Answer:

2.94

Explanation:

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Answer 2

Answer:

(1) 2.94 m

Explanation:

Mass percent is percentage by the mass of solute present in the solution.

Given , Mass % of urea = 15 %

It means that 15 g of urea is present in 100 g of solution.

Mass of water = 100 - 15 = 85 g = 0.085 kg ( 1g = 0.001 kg)

Mass of urea = 15 g

Molar mass of urea =  60.06 g/mol

The formula for the calculation of moles is shown below:

$moles = \frac{Mass\ taken}{Molar\ mass}$

Thus,

$Moles= \frac{15\ g}{60.06\ g/mol}$

Moles = 0.2498 moles

Molality = Moles / Mass of solvent = 0.2498 / 0.085 = 2.94 m

Option A is correct.