Question

255 g of an aqueous solution contains 5 g of urea. What is the concentration of the solution in terms of molality?
(Molar mass of urea = 60 g/mol)

• A. 0.78 m
• B. 0.33 m
• C. 0.24 m
• D. 0.17 m

Answer 1

The correct option is B 0.33 m

$\text{Molality}=\frac{\text{number of moles of solute}}{\text{total mass of the solvent in g}}\times 1000$

$\text{Number of moles of urea}=\frac{5}{60}mol$

$\text{Mass of solvent}=255-5=250g$

$\text{Molality}=\frac{\frac{5}{60}}{250}\times 1000M=0.33M$