The Inorganic Carbon Complex
121
(
total volume of standard) x (normality of acid x 10 6 )
acid used (ml)
Total alkalinity as l1eq/1 = -------:---c:----------~
volume of sample (ml)
Note: When the total alkalinity is determined on the same solution used for
phenolphthalein alkalinity, the volume of acid required for the phenolphthalein titration
is included in the total ml of standard acid in the total alkalinity calculations (above).
Interpretation of Results. The results obtained from the phenolphthalein and total
alkalinity determinations offer a means for the classification of the three principal forms
of alkalinity present in many water types. The classification ascribes the entire alkalinity
to bicarbonate, carbonate, and hydroxide and assumes the absence of other weak acids of
organic and inorganic composition. It also presupposes the incompatibility of hydroxide
and bicarbonate alkalinities in the same sample.
The alkalinity relationships are expressed by:
a. Carbonate alkalinity is present when the phenolphthalein alkalinity is not zero but is
less than the total alkalinity.
b. Hydroxide alkalinity is present when the phenolphthalein alkalinity is more than onehalf the total alkalinity.
c. Bicarbonate alkalinity is present when the phenolphthalein alkalinity is less than onehalf the total alkalinity.
When P = the phenolphthalein alkalinity and T = the total alkalinity, we can differentiate between the hydroxide, carbonate, and bicarbonate alkalinity (all values in mg/I as
CaC0 3 ). Five conditions are possible:
a. P = O. All alkalinity is bicarbonate.
b. P is less than t T. Bicarbonate and carbonate alkalinity both exist.
Carbonate alkalinity = 2P
Bicarbonate 'alkalinity = T - 2P
c. P = tT. All alkalinity is carbonate.
d. P is greater than t T. Hydroxide and carbonate alkalinity both exist.
Hydroxide = 2P - T
Carbonate = 2(T - P)
e. P = T. All alkalinity is hydroxide.
The conversion of results, based on 0.02N H 2 S0 4 standard acid and a 50-ml sample,
then are related as follows:
Result of titration
(ml of acid added)
P=O
P<~T
P=~T
P>~T
P=T
Alkalinites (expressed as mg/1 as CaC03)'
based on acid titration
Hydroxide
Carbonate
Bicarbonate
0
0
Tx 20
0
2P x 20
(T - 2P) x 20
0
2P x 20
0
(2P - T) x 20
2(T-P) x 20
0
Tx 20
0
0
'The factor of 20 in these computations results from conversion of ml of 0.02N acid in a
50-ml sample to mg/t.
The most acceptable usage when alkalinity is reported is to express the results as
equivalents per units volume, i.e., in milliequivalents per liter.
Acid that is 0.02N contains 0.02 meq of acid in each ml, so that each ml of standard acid
used in the titration is equal to 0.02 meq of bicarbonate in 100 ml of sample (0.2 meq/t of
sample) or 0.02 meq in 50 ml of sample (0.4 meq/t of sample). Therefore, if 0.02N acid and
121
(
total volume of standard) x (normality of acid x 10 6 )
acid used (ml)
Total alkalinity as l1eq/1 = -------:---c:----------~
volume of sample (ml)
Note: When the total alkalinity is determined on the same solution used for
phenolphthalein alkalinity, the volume of acid required for the phenolphthalein titration
is included in the total ml of standard acid in the total alkalinity calculations (above).
Interpretation of Results. The results obtained from the phenolphthalein and total
alkalinity determinations offer a means for the classification of the three principal forms
of alkalinity present in many water types. The classification ascribes the entire alkalinity
to bicarbonate, carbonate, and hydroxide and assumes the absence of other weak acids of
organic and inorganic composition. It also presupposes the incompatibility of hydroxide
and bicarbonate alkalinities in the same sample.
The alkalinity relationships are expressed by:
a. Carbonate alkalinity is present when the phenolphthalein alkalinity is not zero but is
less than the total alkalinity.
b. Hydroxide alkalinity is present when the phenolphthalein alkalinity is more than onehalf the total alkalinity.
c. Bicarbonate alkalinity is present when the phenolphthalein alkalinity is less than onehalf the total alkalinity.
When P = the phenolphthalein alkalinity and T = the total alkalinity, we can differentiate between the hydroxide, carbonate, and bicarbonate alkalinity (all values in mg/I as
CaC0 3 ). Five conditions are possible:
a. P = O. All alkalinity is bicarbonate.
b. P is less than t T. Bicarbonate and carbonate alkalinity both exist.
Carbonate alkalinity = 2P
Bicarbonate 'alkalinity = T - 2P
c. P = tT. All alkalinity is carbonate.
d. P is greater than t T. Hydroxide and carbonate alkalinity both exist.
Hydroxide = 2P - T
Carbonate = 2(T - P)
e. P = T. All alkalinity is hydroxide.
The conversion of results, based on 0.02N H 2 S0 4 standard acid and a 50-ml sample,
then are related as follows:
Result of titration
(ml of acid added)
P=O
P<~T
P=~T
P>~T
P=T
Alkalinites (expressed as mg/1 as CaC03)'
based on acid titration
Hydroxide
Carbonate
Bicarbonate
0
0
Tx 20
0
2P x 20
(T - 2P) x 20
0
2P x 20
0
(2P - T) x 20
2(T-P) x 20
0
Tx 20
0
0
'The factor of 20 in these computations results from conversion of ml of 0.02N acid in a
50-ml sample to mg/t.
The most acceptable usage when alkalinity is reported is to express the results as
equivalents per units volume, i.e., in milliequivalents per liter.
Acid that is 0.02N contains 0.02 meq of acid in each ml, so that each ml of standard acid
used in the titration is equal to 0.02 meq of bicarbonate in 100 ml of sample (0.2 meq/t of
sample) or 0.02 meq in 50 ml of sample (0.4 meq/t of sample). Therefore, if 0.02N acid and