Question

An aqueous solution of ethanol has density $1.025g/mL$ and it is $2M$. What is the molality of this solution?

• A. $1.79$
• B. $2.143$
• C. $1.951$
• D. None of these

Answer 1

Answer: (B)

$2.143$

$2M$ means $2$ moles of ethanol in $1L$ of solution.

$\therefore 2$ moles= $46\times 2=92g$ of ethanol

Mass of solution= $1000\times 1.025=1025g$

Mass of $H_{2}O=1025-92=933g$

$\therefore$ Molality= $\frac{\text{Moles of solute}}{\text{Mass of water in kg}}$

$=\frac{2}{933}\times 1000=2.143M$