Question

The molality of $NaOH$ solution whose density is $1.050{\text{g mL}}^{-1}$ is $2m$. What is the molarity of this solution?

• A. $2.00M$
• B. $1.90M$
• C. $2.05M$
• D. $1.94M$

Answer 1

The correct option is D $1.94M$

It is given that the density of the solution is $1.050{\text{g mL}}^{-1}$.

The concentration of sodium hydroxide solution is $2.0$ molal.

This implies $1000$ g of water has $2$ moles of $NaOH$.

$2$ moles of $NaOH$ $=2\times 40=80g$ of $NaOH$

Mass of solution $=1000+80=1080g$

Volume of solution, $V=\frac{\text{Mass}}{\text{Density}}=\frac{1080}{1.05}=1028.6mL$

Molarity, $M=\frac{\text{Number of moles}}{\text{Volume in L}}=\frac{2}{\frac{1028.6}{1000}}=1.94M$

Hence, the molarity of the solution is $1.94M$.