What is the pH of a solution with a hydroxide concentration of 2.5 x 10^-9 M?

To determine the pH of a solution when given the hydroxide ion concentration, it is essential to utilize the relationship between pH, pOH, and the ion concentrations.

First, we can calculate the pOH using the formula:

pOH = -log[OH⁻]

Substituting the provided hydroxide concentration:

pOH = -log(2.5 x 10^-9)

Calculating this will give a pOH of approximately 8.6.

Next, we can find the pH using the relationship between pH and pOH, which is:

pH + pOH = 14

By rearranging this equation, we can solve for pH:

pH = 14 - pOH

Substituting the value calculated for pOH:

pH = 14 - 8.6 = 5.4

Thus, the pH of the solution is 5.4. This means that the solution is slightly acidic, as a pH of 7 is neutral, and values lower than 7 indicate acidity. This process highlights the importance of understanding the relationships between hydroxide and hydrogen ion concentrations when determining pH levels in solutions.