Advanced Placement (AP) Chemistry Practice Exam

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What is the relationship between pOH and hydroxide ion concentration?

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

The correct answer is: -log [OH-]

The relationship between pOH and hydroxide ion concentration is defined mathematically by the equation pOH = -log[OH⁻]. This means that the pOH value is the negative logarithm of the concentration of hydroxide ions present in a solution. In this context, a higher concentration of hydroxide ions will result in a lower pOH value, indicating a more basic solution. Conversely, a lower concentration of hydroxide ions correlates with a higher pOH value, suggesting a less basic or more neutral solution. The other options refer to different chemical concepts. For instance, -log[H⁺] relates to pH, which measures hydrogen ion concentration instead. The options -log[Ka] and -log[Kb] pertain to acid and base dissociation constants, respectively, which are important for understanding the strengths of acids and bases but do not define the relationship between pOH and hydroxide ion concentration. Thus, the correct choice reflects the specific definition of pOH in relation to hydroxide ions.