This scale for measurement was introduced by Sorenson in 1909 to facilitate dealing with hydrogen ion concentrations. This avoids the need to deal with negative indices and to accommodate the very wide range of H+ and OH~ solutions that are encountered in acid-base reactions, when measured in nanomoles per litre.
The pH is the negative logarithm to base 10 of H ion activity. Acidic solutions always have a pH less than 7.0. The pH scale is an exponential scale, where a 0.3 unit fall in pH reflects a doubling of hydrogen ion concentration.
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