Question

The concentration of $O{H}^{-}$ ion in a water sample is measured as 17 mg/L at ${25}^{\circ }$C. What is the pH of the water sample?

• A. 10
• B. 12
• C. 11
• D. 13

Answer 1

The correct option is C 11

(b) $pOH=-log\left[O{H}^{-}\right]$

where $\left[O{H}^{-}\right]$ is concentration of $O{H}^{-}$ ions in moles per litre

$Moles=\frac{Weightingm}{Molecularmass}=\frac{17\times {10}^{-3}}{17}$

$\therefore MolesofO{H}^{-}={10}^{-3}$

$\therefore pOH=-log\left[{10}^{-3}\right]$

$\Rightarrow pOH=3$

But pH + pOH = 14

$\Rightarrow pH=14-3$

$\Rightarrow pH=11$