PH Basics

Overview
  • Hydrogen ions (H+) can exist freely within water solutions, unbound by other molecules. However, fluid concentrations of free H+ concentration can range over orders of magnitude, making it inconvenient to write the H+ concentration with arabic numerals or even scientific notation. The pH notation was developed as a means of easily indicating the free hydrogen concentration in fluids. The pH of a fluid is related to the base 10 logarithm of its free hydrogen ion concentration. Consequently, the pH scale is not linear and a 1 unit change in pH indicated a 10-fold change in the hydrogen ion concentration.
Derivation
  • pH = -log10[H+]
Example
  • Let us assume that the H+ concentration of a fluid is 4 x 10-8 mol/L
  • Therefore: pH = -log10[4 x 10-8]
  • Consequently, the pH of the fluid is pH = 7.4