Question

As the [H+] in a solution decreases, what happens to the [OH–]? A. It increases and the pH increases. B. It increases and the pH decreases. C. It increases and the pH stays constant. D. It decreases and the pH increases. E. It decreases and the pH decreases.

Answer 1

Answer;

D. It decreases and the pH increases.

Explanation;

• pH is a measure of the hydorgen ion concentration of a solution. Solutions with a high concentration of hydrogen ions have a low pH and solutions with a low concentrations of H+ ions have a high pH.
• [H+] and [OH-] are inversely related. Therefore; As the concentration of H+ increases the pH decreases. Since the concentrations of H+ and OH- are inversely proportional, as one goes up, the other goes down.
• Therefore, an increase in OH- concentration will correspond to an increase in pH and a decrease in the concentration of H+.

Answer 2

Answer : The correct option is, (A) It increases and the pH increases.

Explanation :

pH : It is defined as the negative logarithm of hydrogen ion concentration.

Mathematical expression is,

$pH=-\log [H^+]$

pH is indirectly proportional to the concentration of hydrogen ion.

As per question, when the concentration of hydrogen ion decrease that means the the value of pH increases. When the value of pH increases that means the solution is basic and the concentration of hydroxide ion increases.

Hence, as the $[H^+]$ in a solution decreases, the $[OH^-]$ increases and pH also increases.