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pH MEASUREMENT AND VALUE
What does the pH value of a pH measurment mean?
The water molecule has the property of dissociating into two ionic components in aqueous solutions.
H2O <-> H+ + OH-
The H+ ion is termed hydrogen ion or proton, the OH- ion hydroxide ion.
The pH value describes the activity of hydrogen ions in aqueous solutions on a scale of -1 to 15. Based on
this pH scale, liquids are characterized as being acidic, alkaline or neutral: a solution which is neither acidic
or alkaline is neutral. This corresponds to a value of 7 on the pH scale. Acidity indicates a higher
activity of hydrogen ions and a pH measurement value lower than 7. Alkaline solutions are characterized by
a lower hydrogen ion activity or higher hydroxide ion activity, respectively and a pH measurement value above
7. The graph below uses examples to illustrate the pH scale.
The pH scale is logarithmic. A difference of one pH measurement unit represents a tenfold, or ten times
increase or reduction of hydrogen ion activity in the solution. This explains how a solution’s aggressiveness
increases with the distance from the neutral point.
The pH value can be measured using electrochemical measuring systems, litmus paper, indicators and
colorimeters. Of these methods, electrochemical sensor pH measurements provide the most accurate results.
The pH measurement electrode, like the Vario, is an electrochemical sensor
which consists of a measuring electrode and a reference electrode. The pH measurement electrode is made of
special glass which, due to its surface properties, is particularly sensitive to hydrogen ions. It is filled
with a buffer solution which has a pH value of 7. When placing the pH measurement electrode into a test
solution, the change in voltage is measured by the pH electrode by comparing the measured voltage to the stable
reference electrode. This change is recorded by the pH meter, like the pH315
Water Proof pH Meter, and converted into the pH measurement value displayed.
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