pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

 

 

Meaning of pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

pH (Hydrogen Ion Concentration, or Potential of Hydrogen) (1) A convenient method of expressing the acidity or basicity of a solution in terms of the logarithm of the reciprocal (or negative logarithm) of the hydrogen ion concentration. The pH scale runs from 0 to 14, a pH value of 7.0 indicates a neutral solution. Values above 7.0 pH indicate basicity (basic or alkaline solutions), those below 7.0 pH indicate acidity (acidic solutions). Natural waters usually have a pH between 6.5 and 8.5. Because the units are derived from common logarithms, a difference of one pH unit indicates a tenfold (101) difference in acidity, similarly, a difference of two units indicates a hundredfold (102) difference in acidity. The term originally derived from “potential of hydrogen,” or hydrogen power. (2) A term indicating the hydrogen ion concentration of a solution, i.e., a measure of the solution’s acidity. The term (from French, pouvoir hydrogène, or literally, “hydrogen power”) is defined as the negative logarithm of the concentration of H+ ions (protons): pH = –log10 H+, where H+ is the concentration of H+ ions in moles per liter (see Mole). Because H+ ions associate with water molecules to form hydronium (H3O+) ions (see Acid and Base), pH also is often expressed in terms of the concentration of hydronium ions. In pure water at 22° C (72° F),H3O+ and hydroxyl (OH–) ions exist in equal quantities, the concentration of each is 0.107 moles/liter. Consequently, the pH of pure water is –log (0.107), which equals log 107, or 7. If an acid is added to water, however, an excess of H3O+ ions is formed, their concentration can range between 0.106 and 0.10 moles/liter, depending on the strength and amount of the acid. Therefore, acid solutions have a pH ranging from 6 (for a weak acid) to 1 (for a strong acid). Inversely, a basic solution has a low concentration of H3O+ ions and an excess of OH– ions, and the pH ranges from 8 (for a weak base) to 14 (for a strong base). The presence and concentration of many dissolved chemical constituents found in water are, in part, influenced by the hydrogen-ion activity of water. Biological processes including growth, distribution of organisms, and toxicity of the water to organisms are also influenced, in part, by the hydrogen-ion activity of water.

 

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Author of the Water Words Dictionary source of text: Gary A. Horton

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pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

 

pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

 

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pH (Hydrogen Ion Concentration, or Potential of Hydrogen)

 

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pH (Hydrogen Ion Concentration, or Potential of Hydrogen)