What is the concentration of \(OH ^{-}\)ions of an aqueous solution of \(pH 4.4\) ?
A. \(9.600 \times 10^{-10} moldm ^{-3}\)
B. \(2.512 \times\) \(10^{-10}\) moldm \(^{-3}\)
C. \(9.600 \times 10^{-11}\) moldm \(^{-3}\)
D. \(2.512 \times 10^{-11}\) moldm\(^{-3}\)
Correct Answer: B
Explanation
\begin{aligned}
& pH =-\log _{10}\left[ H ^{+}\right] \\
&{\left[ H ^{+}\right]=10^{- pH }} \\
&=10^{-4.4}=3.98 \times 10^{-5} M \\
&{\left[ H ^{+}\right]\left[ OH ^{-}\right]=10^{-14}} \\
&{\left[ OH ^{-}\right]=\frac{10^{-14}}{\left[H^{+}\right]}=\frac{10^{-14}}{10^{-4.4}}=10^{-14+4.4}} \\
&=10^{-9.6}=2.512 \times 10^{-10} moldm ^{-3}
\end{aligned}
