Question

The mole fraction of solute in aqueous urea solution is $0.2$. The mass percent of solute is:

• A. $45.45\%$
• B. $43.34\%$
• C. $34.23\%$
• D. $35.67\%$

Answer 1

The correct option is A $45.45\%$

The mole fraction of urea is $0.2$.

The mole fraction of water is $1-0.2=0.8$.

The molar masses of urea and water are $60$ g/mol and $18$ g/mol respectively.

Let us say one mole of the total solution is present.

The number of moles of urea and water present will be $0.2$ mol and $0.8$ mol. Their masses will be $0.2\times 60=12$ g urea and $0.8\times 18=14.4$ g water.

The mass percentage of solution $=\frac{Massofurea}{Totalmassofsolution}=\frac{12}{12+14.4}\times 100=45.45$ %.