Question

Calculate the molar hydroxide ion concentration at pH 9

Answer 1

To find the molar hydroxide ion concentration \([OH^-]\) at a given pH, you can use the relationship between pH, pOH, and the concentration of hydroxide ions in water.

1. **Calculate pOH**:
The relationship between pH and pOH is given by:
\[
pH + pOH = 14
\]
So, if the pH is 9:
\[
pOH = 14 - pH = 14 - 9 = 5
\]

2. **Calculate \([OH^-]\)**:
The concentration of hydroxide ions can be calculated from pOH using the formula:
\[
[OH^-] = 10^{-pOH}
\]
Therefore:
\[
[OH^-] = 10^{-5} \, \text{M}
\]

3. **Final Result**:
The molar hydroxide ion concentration at pH 9 is:
\[
[OH^-] = 1.0 \times 10^{-5} \, \text{M}
\]