Which statement correctly defines pOH?

Which statement correctly defines pOH?

• A. The pH of a solution.
• B. The negative logarithm of hydrogen ion concentration.
• C. The negative logarithm of hydroxide ion concentration.
• D. The ratio of pH to pOH.

Answer: (C)

pOH is defined as the negative logarithm of the hydroxide ion concentration: pOH = −log[OH−]. This parallels the definition of pH, which is −log[H+], so pOH specifically measures basicity by looking at how much hydroxide is present in solution. The statement involving hydrogen ion concentration describes pH, not pOH, so it’s not the correct definition for pOH. The idea of a ratio between pH and pOH isn’t a standard definition either. At 25°C, pH and pOH are related by pH + pOH ≈ 14, which helps connect the two concepts.

pOH is defined as the negative logarithm of the hydroxide ion concentration: pOH = −log[OH−]. This parallels the definition of pH, which is −log[H+], so pOH specifically measures basicity by looking at how much hydroxide is present in solution. The statement involving hydrogen ion concentration describes pH, not pOH, so it’s not the correct definition for pOH. The idea of a ratio between pH and pOH isn’t a standard definition either. At 25°C, pH and pOH are related by pH + pOH ≈ 14, which helps connect the two concepts.