Question

An acid solution of pH=6 is diluted 1000 times, the pH of the final solution becomes

• A. 6.01
• B. 9
• C. 3.5
• D. 6.99

Answer 1

Answer: (D)

6.99

$\because pH=6$
$\therefore H^{+}={10}^{-6}M$
After dilution $\left[H^{+}\right]=\frac{{10}^{-6}}{1000}={10}^{-9}M$
$\therefore \left[H^{+}\right]$ from $H_{2}O$ cannot be neglected.
Total $\left[H^{+}\right]={10}^{-9}+{10}^{-7}$
$={10}^{-7}({10}^{-2}+1)$
$={10}^{-7}\left(1.01\right)$
$pH=-log(1.01\times {10}^{-7})$
$=7-0.0043$
$=6.9957$