Question

The pH of an HCl solution is 2. Sufficient water is added to make the pH of the new solution is 5.0. The hydrogen ion concentration is reduced:A. ten foldB. sevenfoldC. thousand foldD. hundred fold

Hint: The pH of a solution is the negative logarithm of hydrogen ion concentration. So, substitute the values of hydrogen ion concentration in both cases and compare them to arrive at the answer.

Complete step by step answer:
We know the formula for the pH. When we substitute the value of the pH of an HCl solution:
That is, ${\text{pH = 2}}$ so, ${\text{[}}{{\text{H}}^{\text{ + }}}{\text{] = 1}}{{\text{0}}^{{\text{ - 2}}}}$
${\text{pH = 5}}$ So, ${\text{[}}{{\text{H}}^{\text{ + }}}{\text{] = 1}}{{\text{0}}^{{\text{ - 5}}}}$.
If we want to make the pH of 5, then:
${\text{[}}{{\text{H}}^{\text{ + }}}{\text{]}}$ Reduced to$\dfrac{{{\text{1}}{{\text{0}}^{{\text{ - 2}}}}}}{{{\text{1}}{{\text{0}}^{{\text{ - 5}}}}}}{\text{ = 1}}{{\text{0}}^{\text{3}}}$.
That is the hydrogen ion concentration is reduced to option (c) thousand folds.