Question

pH of a solution of a strong acid is $\mathrm{5.0.}$ What will be the pH of the solution obtained after diluting the given solution 100 times?

• A. $6.6$
• B. $2.7$
• C. $7$
• D. $3.01$

Answer 1

Answer: (A)

$pH=5,[H^{+}]=10^{-5}mol{L}^{-1}$
On 100 times dilution, $[H^{+}]=10^{-7}mol{L}^{-1}$
$\therefore pH=7$
It is not possible. This indicates that solution is very dilute. Hence,
Total hydrogen ion concentration, [$H^{+}]$
$=\left[\begin{array}{c}Contributionof\\ H_3{O}^{+}ion\\ concentration\\ ofacid\end{array}\right]+\left[\begin{array}{c}Contributionof\\ H_3{O}^{+}ion\\ concentration\\ ofwater\end{array}\right]$
$=10^{-7}+10^{-7}.$
$pH=2\times 10^{-7}=7-log2=7-0.3010=6.6990$