CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Electrometrical measurement of the pH of water. The pH of a solution is a measure of the amount of free hydrogen ions present. This indicates acidity and alkalinity. The more free ions present, the more acidic the solution is said to be. Here, the pH meter is showing 5.48, indicating weakly acidic water. The scale runs from 0-14, with pure (distilled and deionised) water considered neutral at pH 7. There are several reasons why water may deviate from pH 7, including the presence of dissolved salts and gases.
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