Question

$8$ g of $NaOH$ is present in $250$ mL of a solution. The $pH$ of the solution is:

• A. $13.9$
• B. $10.5$
• C. $3.4$
• D. $0.1$

Answer 1

Answer: (A)

$13.9$

The number of moles of $NaOH$ in $8$ g $=\frac{8}{40}=0.2$ mol (Molecular weight of $NaOH=40$ g/mol).
Molarity of $\left[O{H}^{-}\right]=\frac{0.2}{0.25}$

$=0.8$ M.
Therefore, $pH=14+\log \left[O{H}^{-}\right]$

$=14+\log \left(0.8\right)$

$=14-0.1$

$=13.9$.