The sum of pH and pOH at 25 degrees Celsius is always equal to 14. This is because pH and pOH are measures of the acidity or basicity of a solution, and the neutral point at which a solution is neither acidic nor basic has a pH of 7 and a pOH of 7.

The pH of a solution is defined as the negative logarithm of the hydrogen ion concentration, while the pOH is defined as the negative logarithm of the hydroxide ion concentration. The relationship between pH and pOH can be expressed as follows:

$$pH + pOH = 14$$

This equation holds true at all temperatures, but the values of pH and pOH that correspond to the neutral point will vary depending on temperature. At 25 degrees Celsius, the neutral point has a pH of 7 and a pOH of 7.

Knowing the relationship between pH and pOH can be useful for understanding the acidity or basicity of a solution and for performing calculations involving hydrogen ion and hydroxide ion concentrations.