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pH is a unit of measure which describes the degree of acidity or
alkalinity of a solution. It is measured on a scale from 0 to 14. The term
pH is derived from “p”, the mathematical symbol of the negative
logarithm, and “H”, the chemical symbol of Hydrogen. The definition of
pH is the negative logarithm of the Hydrogen ion activity.
pH = -log[H+]
Thus pH provides the needed quantitative information by expressing the
degree of activity of an acid or base in terms of hydrogen ion activity.
Acid and bases have both free hydrogen and hydroxyl ions. Since the
relationship between hydrogen ions and hydroxyl ions in a given solution
is constant for a given set of conditions, either one can be determined by
knowing the other. If the ratio of the hydrogen ion is greater than that
of the hydroxyl ion the solution is acidic, and has a pH value below 7. If
the ratio of the hydroxyl ion is greater than that of the hydrogen ion the
solution is basic, and has a pH value above 7. If the ratio of the
hydroxyl ion is equal to that of the hydrogen ion the solution is neutral,
and has a pH value of 7. Thus, pH is a measurement of both acidity and
alkalinity, even though by definition it is a selective measurement of
hydrogen ion activity. A rough indication of pH can be obtained using pH
papers or indicators, which change color as the pH level varies. These
indicators are very limited in their accuracy and can be difficult to
interpret correctly. A more accurate way to determine pH is by using a pH
meter. The pH meter electrode can be looked at as a simple battery, with a
voltage that varies with the pH of a measured solution. This voltage is
then amplified and displayed providing an accurate and repeatable reading
for analysis. There is a wide variety of applications for pH measurement.
For example, pH measurement and control is the key to the successful
purification of drinking water, sewage treatment, food processing,
electroplating, and the effectiveness and safety of medicines. etc. Plants
require the soil to be within a certain pH level to grow properly, and
animals can sicken or die if their blood pH level is not within certain
levels. The efficient and balanced control of a solutions pH is easily
controlled by either the addition of a base or acid to neutralize a
solution as required.
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Common Substances
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pH values
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Household Lye
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13.6
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Bottle Washing
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13.1
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Ammonia
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11.4
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Borax
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9.3
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Sea Water
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8.0
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Swimming Pool
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7.4
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Distilled Water
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7.0
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Food Processing
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5.0
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Boric Acid
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5.0
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Battery Acid
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0.37
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