ABSTRACT
A vast array of chemical reactions occurring in the soil environment involves either the consumption or the release of protons. Because proton activity is a controlling factor in many chemical processes, the pH of a soil solution is considered a master chemical variable. The pH of a solution is defined as the negative common logarithm (denoted by “p”) of the hydrogen ion (H+) activity. A common misconception is that the pH of a solution is the negative logarithm of the molar concentration of the hydrogen ion. As will be shown in a later section, the pH electrode, which is an ion selective electrode that senses protons, responds to H+ activity. Therefore, the pH electrode is providing a measure of the true activity of the proton in solution.
