LaMotte HYDROXIDE, PHENOLPHTHALEIN & TOTAL ALKALINITY TEST KIT WAT-MPH-DR - Manual (Page 4)

CAL CU LA TION OF AL KA LIN ITY RE LA TION SHIPS
The results obtained from the Phenolphthalein and Total Alkalinity
determinations offer a means for the stoichiometric classification of the
three principal forms of alkalinity present in many water supplies. The
classification ascribes the entire alkalinity to bicarbonate, carbonate, and
hydroxide; and assumes the absence of other weak acids of inorganic or
organic composition, such as silicic, phosphoric, and boric.
This classification system further presupposes the incompatibility of
hydroxide and bicarbonate alkalinities in the same sample. Since the
calculations are on a stoichiometric basis, ion concentrations in the
strictest sense are not represented in the results.
According to this scheme:
A.
Carbonate Alkalinity is present when the Phenolphthalein
Alkalinity is not zero but is less then the total alkalinity.
B. Hydroxide Alkalinity is present if the Phenolphthalein is more than
one-half the total alkalinity.
C. Bicarbonate Alkalinity is present if the Phenolphthalein Alkalinity
is less than one-half the total alkalinity.
The mathematical conversion of the results is shown in the table below:
Relationships Between Phenolphthalein Alkalinity, Total
Alkalinity, Carbonate Alkalinity & Hydroxide Alkalinity
Result of
Titration
Hydroxide
Alkalinity as
CaCO
3
Carbonate
Alkalinity as
CaCO
3
Bicarbonate
Alkalinity as
CaCO
3
P = 0 0 0 T
P < a T 0 2P T - 2P
P = a T 0 2P 0
P > a T 2P - T 2 (T - P) 0
P = T T 0 0
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10/02