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{{lowercase|title=pH}}{{subpages}}
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'''Potential of hydrogen''' ('''pH''') is a scale that measures the [[acid]]ity or [[alkalinity]] of a solution. Values for pH range usually from 0 (strongly acidic) to 14 (strongly alkaline or basic). The pH of a neutral solution, such as [[Distilled water|pure water]] at room [[temperature]] and atmospheric [[pressure]], is 7, whereas the pH of an acidic solution is less than 7 and the pH of a basic solution is greater than 7. The pH scale is [[logarithm]]ic, meaning that each value is 10 fold the next (for example, a pH of 12 is 10 times more basic than a pH value of 11). <!--I'm sure this can be explained better -->
'''Potential of hydrogen''' ('''pH''') is a scale that measures the [[acid]]ity or [[alkalinity]] of a solution. Values for pH range usually from 0 (strongly acidic) to 14 (strongly alkaline or basic). The pH of a neutral solution, such as [[Distilled water|pure water]] at room [[temperature]] and atmospheric [[pressure]], is 7, whereas the pH of an acidic solution is less than 7 and the pH of a basic solution is greater than 7. The pH scale is [[logarithm]]ic, meaning that each value is 10 fold the next (for example, a pH of 12 is 10 times more basic than a pH value of 11). <!--I'm sure this can be explained better -->
The traditional way to determine the pH value of a liquid is by the change of the colour of [[litmus]] paper.


==Formal definition==
==Formal definition==

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Potential of hydrogen (pH) is a scale that measures the acidity or alkalinity of a solution. Values for pH range usually from 0 (strongly acidic) to 14 (strongly alkaline or basic). The pH of a neutral solution, such as pure water at room temperature and atmospheric pressure, is 7, whereas the pH of an acidic solution is less than 7 and the pH of a basic solution is greater than 7. The pH scale is logarithmic, meaning that each value is 10 fold the next (for example, a pH of 12 is 10 times more basic than a pH value of 11). The traditional way to determine the pH value of a liquid is by the change of the colour of litmus paper.

Formal definition

pH is defined by

Because of concentration of hydronium ions times the concentration of hydroxide ions is constant, namely



where pOH is defined in a manner similar to pH, as shown below.

pH of common items

SubstancespH range
Human gastric juice1 - 3
Limes1.8 - 2.0
Soft drinks2.0 - 4.0
Lemons2.2 - 2.4
Vinegar2.4 - 3.4
Apples2.9 - 3.3
Tomatoes4.0 - 4.4
Beer4.0 - 5.0
Bananas4.5 - 4.7
Human urine4.8 - 8.4
Cow's milk6.3 - 6.6
Human saliva6.5 - 7.5
Human blood plasma7.3 - 7.5
Egg white7.6 - 8.0
Milk of magnesia10.5
Household ammonia11 - 12

References

  • "General Chemistry, 2nd Ed.", pp 103-117, D. D. Ebbing & M. S. Wrighton, Houghton Mifflin, Boston, 1987.
  • "General Chemistry with Qualitative Analysis, 2nd Ed.", pp. 263-278, Saunders College Publishing, Philadelphia, 1984.