Ohio State University

Measures of pH in Water

pH and Acidity

pH is a measure of acidity of the solution through hydrogen ion concentration and is expressed as the molar concentration of the hydrogen ion as its negative logarithm (pH= -log[H+]).

pH is one of the main indicators used for evaluating surface water suitability and quality and is important because aquatic organisms are sensitive to pH changes, especially acidity, in water. Many aquatic organisms respond best to a near neutral pH, but can withstand a range of 6-8.5. pH is an extremely important indicator of water quality because the toxicity of other toxic compounds can be altered if a change in pH occurs.

Testing Information

To test a sample's pH, a glass electrode/meter is used and is calibrated using two buffers. The electrode is then immersed in the sample (after calibration) and a pH value is reported. This is a very common and relatively inexpensive procedure that can offer a lot of information about the water sample. pH testing is a common field analysis where only a small quantity of water (10ml) is required for a satisfactory sample.

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