Sample Calculation: Determine the percent change of pH of a solution given the data below: initial pH of solution = 5.25 final pH of solution = 3.75 Percent Change of pH = 100% X final pH value - initial pH value initial pH value Percent Change of pH = 100% X 3.75 - 5.25 5.25 Percent Change of pH = 100% x -1.50 5.25 Percent Change of pH = -28.57% Percent Change can be positive or negative. A positive result indicates an increase and a negative result indicates a decrease. 1. The pH of a solution is calculated as follows: pH = -log[H*], where [H*] is the hydrogen ion concentration in mol/L, and log is the common logarithm function (base 10 logarithm)