Question

pH of a solution at ${25}^{\circ }C$ is 2. If the pH is to be doubled, then the hydronium ion concentration of the solution should be:

• A. halved
• B. increased to 100 times
• C. doubled
• D. decreased to 100 times

Answer 1

Answer: (D)

decreased to 100 times

$pH=-log\left[H^{+}\right]=2$.
Thus $\left[H^{+}\right]={10}^{-2}$.
The pH is doubled from 2 to 4.
$\left[H^{+}\right]={10}^{-4}$.
Thus the hydronium ion concentration should be decreased to 100 times.