Question

What is the molarity of $4\%$ W/W $NaOH$ solution ?
(Given: density of solution is $1.2g/mL$).

• A. $1.2M$
• B. $1M$
• C. $0.12M$
• D. $12M$

Answer 1

The correct option is A $1.2M$

$4\%$ W/W $NaOH$ means $4g$ of $NaOH$ in $100g$ of solution.
So if we consider the solution to be $100g$, then the no. of moles of $NaOH$ present $=\frac{4}{40}=0.1$
We know that,
Molarity = $\frac{\text{Moles}}{\text{Volume in Litres of the solution}}$
To find the volume, Density $=\frac{\text{Mass}}{\text{Volume}}$
i.e., $1.2=\frac{100}{\text{Volume}}$
$\therefore \text{Volume}=\frac{100}{1.2}mL$
Molarity $=\frac{0.1\times 1.2\times 1000}{100}=1.2M$