Chemistry 102: Acids: pH and pOH calculations

Question

10.

part 1) Write both answers to at least two decimal places.

Calculate the pH of a 0.155 M  solution of KOH.

part 2) Calculate the pOH of a 0.155 M solution of KOH.

Answer 1

The pH of a solution can be calculated by using the following equation:

pH = -log₁₀[H⁺] where [H⁺] is the concentration of hydrogen ions in the solution, or the molarity of the hydrogen ions.

Then, to find pOH, all you have to do is subtract the value of pH from 14 as follows:

pOH = 14 - pH

Alternatively, you can calculate the value of pOH directly by using the following equation:

pOH = -log₁₀[OH^-] where [OH^-] is the concentration of hydroxide ions in the solution, or the molarity of the hydroxide ions.

Then, to find pH, all you have to do is subtract the value of pOH from 14 as follows:

pH = 14 - pOH

Thus, for part 1:

pOH = -log₁₀[OH^-] = -log₁₀[0.155] = 0.81

pH = 14 - 0.81 = 13.19

For part 2:

pOH = -log₁₀[OH^-] = -log₁₀[0.155] = 0.81