Question

A $300g$, $30\%$ (w/w) NaOH solution is mixed with $500g$ $40\%$ (w/w) $NaOH$ solution. What is $\%$ (w/v) $NaOH$, If density of final solution is $2g/ml$.

• A. $72.5$
• B. $65$
• C. $62.5$
• D. $\text{N}one$

Answer 1

The correct option is A $72.5$

$30$% (w/w) of $300g$ of $NaOH$ = $300\times \frac{30}{100}$ = $90g$
$40$% (w/w) of $500g$ of $NaOH$ = $500\times \frac{40}{100}$ = $200g$
Total volume of solution =$\frac{Massofsolution}{Densityofsolution}$.
= $\frac{800}{2}=400mL$
$\%\left(w/v\right)$ volume of $NaOH=\frac{90+200}{400}\times 100=72.5$