What is the pOH of a solution of HNO3 that has [OH - ] = 9.50 * 10-9 M?

The correct answer to that question is

= 8.02

The answer is pOH = 8.022

By definition, pOH = - log₁₀[OH⁻]. Since [OH⁻] = 9.50 * 10⁻⁹ M, we have

pOH = - log₁₀ (9.50 * 10⁻⁹)

= 8.02227

The quantity [OH⁻] = 9.50 * 10⁻⁹ M has three significant figures. Therefore, we need report our final pOH answer to three decimal places. It's a special rule regarding significant figures and logarithms/exponents: For a pH/pOH, only the figures after the decimal places are considered significant. Therefore, the number of significant figures in the concentration will be equal to the number of decimal places in the pOH/pH.

The answer is pOH = 8.022