What is the expression for pOH?

What is the expression for pOH?

• A. pOH = -log[OH-]
• B. pOH = log[OH-]
• C. pOH = -[OH-]
• D. pOH = [OH-]

Answer: (A)

pOH is defined as the negative base-10 logarithm of the hydroxide ion concentration. This gives pOH = -log10[OH-]. The negative sign is essential because [OH-] in solutions is typically less than 1 M, so log10[OH-] would be negative and pOH would become a positive, convenient value that fits with the pH scale (pH + pOH ≈ 14 at 25°C). Using just log[OH-] would miss that conversion to a positive, intuitive measure. Writing -[OH-] or [OH-] would not reflect a logarithmic measure at all, so they don’t correctly describe pOH.

pOH is defined as the negative base-10 logarithm of the hydroxide ion concentration. This gives pOH = -log10[OH-]. The negative sign is essential because [OH-] in solutions is typically less than 1 M, so log10[OH-] would be negative and pOH would become a positive, convenient value that fits with the pH scale (pH + pOH ≈ 14 at 25°C). Using just log[OH-] would miss that conversion to a positive, intuitive measure. Writing -[OH-] or [OH-] would not reflect a logarithmic measure at all, so they don’t correctly describe pOH.