Question

What is the mass of urea required for making $2.5kg$ of $0.25$ molal aqueous solution?

• A. $37g$
• B. $25g$
• C. $125g$
• D. $27.5g$

Answer 1

The correct option is A $37g$

No of moles of urea = $0.25mol$

Mass of solvent = $1000g$

Molar mass of urea = $60g/mol$

Mass of urea in solution =$0.25\times 60=15g$

Total mass of solution = $1000+15=1015g$

Since $1.015kg$ contains $15g$ of urea,

Therefore, $2.5kg$ will contain = $\frac{15}{1.015}\times 2.5=37g$

Hence, option $A$ is correct.