Lamotte com pany – LaMotte HYDROXIDE, PHENOLPHTHALEIN & TOTAL ALKALINITY MPH-DC User 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 attributes the entire alkalinity to bicarbonate, carbonate and
hydroxide, and assumes the absence of other weak acids of inorganic or
organic composition, such as silica, phosphoric and boric.
This classification system assumes 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.
Ac cord ing to this scheme:
A.
Carbonate alkalinity is present when the phenolphthalein alkalinity
is not zero but is less than the total alkalinity.
B.
Hydroxide alkalinity is present if the phenolphthalein alkalinity 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.
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<
1
2
T
0
2P
T-2P
P=
1
2
T
0
2P
0
P>
1
2
T
2 (T-P)
2 (T-P)
0
P=T
T
0
0
LaMOTTE COM PANY
Helping Peo ple Solve An a lyt i cal Chal lenges
SM
PO Box 329 • Chestertown • Mary land • 21620 • USA
800-344-3100 • 410-778-3100 (Out side USA) • Fax 410-778-6394
Visit us on the web at www.lamotte.com
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