In chemistry, pH is a measure of how acidic something is. The lower the number on the pH scale, the more acid a substance contains.

The pH scale goes from 0 to 14, with 0 being the most acidic. The higher, low-acid numbers on the pH scale are basic — they feel slippery and have an astringent taste. Substances at around 7, the middle of the pH scale, are neutral, like water. Lemon juice has a pH of 2.2, since it's acidic. pH comes from the German word Potenz, "potency or power," and H, the chemical symbol for hydrogen.

Definitions of pH
  1. noun
    (from potential of Hydrogen) the logarithm of the reciprocal of hydrogen-ion concentration in gram atoms per liter; provides a measure on a scale from 0 to 14 of the acidity or alkalinity of a solution (where 7 is neutral and greater than 7 is more basic and less than 7 is more acidic);
    synonyms: pH scale
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    pH values below 7
    pH values above 7
    pH value of 7
    excessive acidity
    type of:
    hydrogen ion concentration
    the number of moles of hydrogen ions per cubic decimeter
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