Manual
XXIII. pH and ORP (6Psi)
A.
1.
pH is the measurement of Acidity or Alkalinity of an aqueous solution. It
is also stated as the Hydrogen Ion activity of a solution. pH measures
the effective, not the total, acidity of a solution.
needed quantitative information by expressing the degree of activity of
an acid or base.
In a solution of one known component, pH will indicate concentration
indirectly. However, very dilute solutions may be very slow reading, just
because the very few ions take time to accumulate.
The acidity or alkalinity of a solution is a measurement of the relative
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-
of water, and balance would be 10
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, solutions are less acidic than
neutral, and therefore are alkaline. A concentration of 10
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The active part of the pH sensor is a thin glass surface that is selectively
receptive to hydrogen ions. Available hydrogen ions in a solution will
accumulate on this surface and a charge will build up across the glass
interface. The voltage can be measured with a very high impedance
voltmeter circuit; the dilemma is to connect the voltmeter to solution on
each side.
The glass surface encloses a captured solution of potassium chloride
holding an electrode of silver wire coated with silver chloride. This is
the most inert connection possible from a metal to an electrolyte. It can
still produce an offset voltage, but using the same materials to connect
offsets to cancel.