Question

$250mL$ of a $2\%\left(w/v\right)NaOH$ solution is diluted up to $600mL$. Find the resultant molarity of the solution.

• A. $4.0M$
• B. $0.166M$
• C. $0.33M$
• D. $0.21M$

Answer 1

The correct option is D $0.21M$

$2\%\left(w/v\right)$ solution means $2g$ of $NaOH$ is present in $100mL$ of the solution.
$\text{Number of moles of}NaOH=\frac{\text{given mass of}NaOH}{\text{molar mass}}$
$=\frac{2}{40}=0.05$

$\text{Molarity}=\frac{\text{number of moles of solute}}{\text{volume of solution in mL}}\times 1000$

$\text{Molarity}=\frac{0.05}{100}\times 1000=0.5M$
Conserving moles before and after dilution:
$M_1{V}_1=M_2{V}_2$
Where, $M_1=0.5M$ and $V_1=250mL$
$M_2$ and $V_2$ are the molarity and volume of the resultant solution.
$(0.5\times 250)=(M\times 600)$
$M=0.21M$

Molarity of the resultant solution is $0.21M$.