Question

$3.0$ molal sodium hydroxide solution has a density of $1.110{\text{g mL}}^{-1}$. The molarity of this solution is:

• A. $2.97M$
• B. $3.05M$
• C. $3.65M$
• D. $4.11M$

Answer 1

The correct option is A $2.97M$

It is given that the density of the solution is $1.110{\text{g mL}}^{-1}$.

The concentration of sodium hydroxide solution is $3.0$ molal.

This implies $1000$ g of water has $3$ moles of $NaOH$.

$3$ moles of $NaOH$ $=3\times 40=120$ g of $NaOH$

Mass of solution $=1000+120=1120$ g

Volume of solution $=\frac{\text{Mass}}{\text{Density}}=\frac{1120}{1.11}=1009$ mL

Molarity $=\frac{\text{Number of moles}}{\text{Volume in L}}=\frac{3}{\frac{1009}{1000}}=2.97M$

Hence, the molarity of the solution is $2.97M$.