Question

The pH of a solution is 4. Concentration of $O{H}^{–}$ ions in the solution is

• A. $1\times {10}^{-11}mol{L}^{-1}$
• B. $1\times {10}^{-4}mol{L}^{-1}$
• C. $1\times {10}^{-10}mol{L}^{-1}$
• D. $1\times {10}^{-14}mol{L}^{-1}$

Answer 1

The correct option is C $1\times {10}^{-10}mol{L}^{-1}$

The pH of a solution is calculated as:

$pH=-\log \left[H^{+}\right]$

$4=-\log \left[H^{+}\right]$

Concentration of $H^{+}ions=\left[H^{+}\right]=1\times {10}^{–4}mol{L}^{–1}$

Now, $\left[H^{+}\right]\left[O{H}^{–}\right]={10}^{–14}$

∴ $1\times {10}^{–4}\left[O{H}^{–}\right]={10}^{–14}$

Concentration of $O{H}^{–}ions=\left[O{H}^{–}\right]=1\times {10}^{–14}+{10}^4=1\times {10}^{–10}mol{L}^{–1}$

Hence, the correct answer is option (c).