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MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont)

pH: The pH of aqueous solution is controlled by the interrelated chemical reactions that produce or consume hydrogen ions. The pH of a solution is a measure of the effective hydrogen-ion concentration. More specifically, pH is a measure that represents the negative base-10 logarithm of hydrogen-ion activity of a solution, in moles per liter. Solutions having a pH below 7 are described as acidic, and solutions with pH greater than 7 are described as basic or alkaline. Dissolved gases such as carbon dioxide, hydrogen sulphide and ammonia, apparently affect pH. Dagasification (for example, loss of carbon dioxide) or precipitation of a solid phase (for example, calcium carbonate) and other chemical, physical, and biological reactions may cause the pH of a water sample to change appreciably soon after sample collection.

The electrometric pH-measurement method, using a hydrogen-ion electrode, commonly is used in continuous water-quality pH sensors.

A correctly calibrated pH sensor can accurately measure pH to -+ 0.2 pH units; however, the sensor can be stretched, broken or fouled easily. If the streamflow rates are high, the accuracy of the pH measurement can be affected by streaming-potential effects.

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