Question

The pH of a solution is 5.00. To this solution, sufficient acid is added to lower the pH to 2.00. The corresponding increase in $H_3{O}^{\oplus }$ ion concentration is:

• A. 1000 times
• B. 2.5 times
• C. 100 times
• D. 5 times

Answer 1

The correct option is A 1000 times

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

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

let increase in concentration is ${10}^x$

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

So, ${10}^x\times {10}^{-5}={10}^{-2}$

$\Rightarrow x=3$

So, hydrogen ion concentration increases by 1000 times.