Question

If you are given a $4\text{m}$ $NaOH$ solution having density $2\text{g/mL}$, then find the molarity of the solution.

• A. $4.59\text{M}$
• B. $6.89\text{M}$
• C. $0.345\text{M}$
• D. $0.48\text{M}$

Answer 1

The correct option is B $6.89\text{M}$

Let mass of the solvent be $1000\text{g}$.
So, $4\text{m}$ $NaOH$ solution means $4\text{mol}$ of $NaOH$ in $1000\text{g}$ solvent.
We know, molar mass of $NaOH=40\text{g/mol}$

Hence $4\text{mol}$ of $NaOH=160\text{g}$
Total mass of solution = mass of solution + mass of solvent$=(160+1000)\text{g}$
Given, density of the solution $=2\text{g/mL}$
So, the volume of the solution $\frac{1160}{2}\text{mL}$ $=580mL=0.58L$
$\therefore \text{Molarity}\text{M}=\frac{\text{number of moles of solute}}{\text{volume of the solution in L}}$ = $\frac{4}{0.58}=6.89M$