Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Symbol for the picohenry, an SI unit of electrical inductance equal to 10−12 henrys.
  • abbr. The negative of the logarithm to the base 10 of the concentration of hydrogen ions, measured in moles per liter; a measure of acidity or alkalinity of a substance, which takes numerical values from 0 (maximum acidity) through 7 (neutral) to 14 (maximum alkalinity).

Etymologies

p(otential of) h(ydrogen).
(American Heritage® Dictionary of the English Language, Fourth Edition)
From p, denoting negative logarithm, and H, denoting hydrogen. (Wiktionary)

Examples

  • The term pH is a convenient way to express the concentration of hydrogen ions (H+) in an aqueous solution.

    PH

  • And if the pH is above 3.3, it moves to Medium Sweet, and if the pH is as low as 2.9 or lower, the wine moves to Dry.

    Rants

  • In regular soap, fats or oils are boiled with an alkali agent, such as lye or wood-ash, and the resulting mess which comes from this combination of heat and pH is a solid substance with a curious molecular makeup.

    A Bit of Soap

  • Ratio above 4.1, but using the pH adjustment, a sweeter wine with a ratio of, say, 4.4 might actually be moved to Medium Sweet if the pH is significantly lower.

    Rants

  • But if the pH is 3.3 or 3.4, it moves up to Medium Dry.

    Rants

  • And if the pH is 2.8 or below (highly unlikely), the wine could be called Dry.

    Rants

  • If your soil pH is adequate (7.0 to 7.5) Alfalfa can work as it will root quite deeply given adequate soil (read deep) prep and proper pH.

    FoodPlot Choices

  • The consequences of this drop in pH levels is pretty severe.

    Ocean Acidification: Another Carbon Challenge | Heretical Ideas Magazine

  • The first was a rise in pH to over 9.0 in the unbuffered suspension, as a result of the alkaline nature of the glass surfaces (pH being measured with a semi-micro glass electrode that I constructed).

    Robert F. Furchgott - Autobiography

  • The energy liberated during the electron transport is used to pump protons across the membranes, so that a difference in pH and electrical potential between the two sides is created.

    Press Release: The 1988 Nobel Prize in Chemistry

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