pH describes the acidity or alkalinity of a solution. A low pH indicates acidic conditions, and a high pH indicates basic conditions.
pH is actually a measure of the amount of hydrogen ions in solution. In fact, some people think of it as being the “power of hydrogen.” A low pH has a large number of free hydrogen ions in the water, whereas a high pH has relatively few. Technically, pH is the negative logarithm of the free hydrogen activity in solution.
pH is highly important and is used to monitor for safe water conditions. Many animals cannot live in a pH level below 5 or above 9. Once the normal pH range for a water has been established, a rise or fall in pH can indicate chemical pollution, or acid rain.
pH is measured on a scale of 0 to 14; 7 is neutral, below 7 is acidic, greater than 7 is basic. A lower number represents a greater number of hydrogen ions, and each pH unit represents a 10-fold change in the hydrogen ion concentration and amount of acidity. For instance, a pH of 6 has ten times more free hydrogen ions than a pH of 7, and one hundred times more free hydrogen ions than a pH of 8.
pH is commonly measured using a combination pH electrode. The pH electrode has a glass bulb filled with a pH 7 solution. The difference between the pH in the water and the pH 7 solution within the glass bulb generates an electrical potential, which is measured relative to a stable electrical potential generated by a reference electrode located within the pH probe. The pH of the solution is then determined by the difference between these two electrical potentials.