Advanced Placement (AP) Chemistry Practice Exam

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What is the formula used to calculate pH?

-log [H+]
-log [OH-]
-log [Ka]
-log [Kb]

The correct answer is: -log [H+]

The formula used to calculate pH is based on the concentration of hydrogen ions (H⁺) in a solution. pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration. This relationship is expressed mathematically as pH = -log[H⁺]. This means that as the concentration of hydrogen ions increases, the pH value decreases, indicating a more acidic solution. Conversely, a lower concentration of hydrogen ions corresponds to a higher pH, indicating a more basic solution. It is a crucial concept in understanding the acidity or basicity of solutions in chemistry and is fundamental in acid-base chemistry, particularly for titration and equilibrium reactions. The other formulas provided involve hydroxide ion concentration, acid dissociation constants, and base dissociation constants, which relate to different aspects of acid-base balance but do not provide the direct measure of pH as defined by hydrogen ion concentration.