LaMotte PHENOLPHTHALEIN/TOTAL ALKALINITY TEST KIT WAT-MP-DR - Manual (Page 3)

CAL CU LA TION OF AL KA LIN ITY RE LA TION SHIPS
Results obtained from Phenolphthalein and Total Alkalinity
determinations offer a means for the stoichiometric classification of three
principal forms of alkalinity present in many water supplies. Classification
attributes the entire alkalinity to bicarbonate, carbonate and hydroxide;
and assumes absence of other weak acids of inorganic or organic
composition, such as silicic, phosphoric, and boric. This classification
system further assumes incompatibility of hydroxide and bicarbonate
alkalinities in the same sample. Since 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 Phenolphthalein Alkalinity is
not zero but less than the Total Alkalinity.
B. Hydroxide Alkalinity is present if Phenolphthalein Alkalinity is more
than one-half the Total Alkalinity.
C. Bicarbonate Alkalinity is present if Phenolphthalein Alkalinity is less
than one-half the Total Alkalinity.
Mathematical conversion of the result is shown in the following table:
Relationships Between Phenolphthalein,
Total, Carbonate, Bicarbonate & 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<1/2T 0 2P T-2P
P=1/2T 0 2P 0
P>1/2T 2P-T 2(T-P) 0
P=T T 0 0