Question

The pH of a solution is $5.0$. To this solution sufficient acid is added to decrease the pH to $2.0$. The increase in hydrogen ion concentration is:

• A. $100$ times
• B. $10$ times
• C. $1000$ times
• D. $2.5$ times

Answer 1

The correct option is C $1000$ times

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

When $pH=5,$

$\left[H^{+}\right]={10}^{-pH}={10}^{-5}M$

The pH of solution is decreased to 2.

When $pH=2,$

$\left[H^{+}\right]={10}^{-pH}={10}^{-2}M$

The change in concentration of $\left[H^{+}\right]$ is ${10}^{-2}/{10}^{-5}={10}^3=1000$

It is increased by 1000 times.