LaMotte ALKALINITY P&T KIT - Manual (Page 2)

8. Reinsert Titrator in cap and continue titration until color changes from green-blue
to pink. Read the test result directly from the scale where the large ring on the
Titrator meets the Titrator barrel. Record as ppm T Alkalinity as CaCO
3
. Be sure
to include in test result value the total amount of titration reagent dispensed (i.e.
see Step 5).
9. If only Total Alkalinity is to be tested, perform Steps 1,7 and 8 only, using a full
Titrator in Step 8.
CALCULATION OF ALKALINITY RELATIONSHIPS
Results obtained from Phenolphthalein and Total Alkalinity determinations offer a
means for the stoichiometric classifi cation of three principal forms of alkalinity pres-
ent in many water supplies. Classifi cation attributes the entire alkalinity to bicarbon-
ate, carbonate and hydroxide; and assumes absence of other weak acids of inorganic or
organic composition, such as silicic, phosphoric, and boric. This classifi cation 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
CaCO3
Carbonate
Alkalinity as
CaCO3
Bicarbonate
Alkalinity as
CaCO3
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
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