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1 Alkalinity

This technical data sheet provides information about alkalinity measurements in water. Alkalinity is expressed using Methyl Orange (MO) and Phenolphthalein (P) indicators, which change color at specific pH values. MO alkalinity includes bicarbonate, carbonate, and hydroxyl, while P alkalinity only includes half the carbonate and all the hydroxyl. The document derives equations to determine the concentrations of bicarbonate, carbonate, and hydroxyl based on the MO and P alkalinity measurements and the pH scale shows which constituents can exist at different pH values in natural and treated waters.

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107 views1 page

1 Alkalinity

This technical data sheet provides information about alkalinity measurements in water. Alkalinity is expressed using Methyl Orange (MO) and Phenolphthalein (P) indicators, which change color at specific pH values. MO alkalinity includes bicarbonate, carbonate, and hydroxyl, while P alkalinity only includes half the carbonate and all the hydroxyl. The document derives equations to determine the concentrations of bicarbonate, carbonate, and hydroxyl based on the MO and P alkalinity measurements and the pH scale shows which constituents can exist at different pH values in natural and treated waters.

Uploaded by

prakash
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© © All Rights Reserved
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TECHNICAL ALKALINITY

DATA SHEET

The alkalinity of the water is expressed in terms of MO and P values. The abbreviations stand for Methyl Orange and Phenolphthalein,
which are complex organic compounds known as indicators and they exhibit the property of changing color at certain pH values. The
Methyl Orange alkalinity measures or represents all of the alkalinity coming from all of the bicarbonate, carbonate, and hydroxyl. The
Phenolphthalein alkalinity is that derived from ½ of the carbonate and all of the hydroxyl.

The derivation of the alkalinity distribution calculations is PH SCALE SHOWING CONSTITUENTS THAT CAN EXIST AT VARIOUS
made as follows: PH VALUES IN NATURAL AND TREATED WATERS

1. MO alkalinity = HCO3 + CO3 + OH 14.0


2. P alkalinity = ½ CO3 + OH 13.0 CAUSTIC OR HYDROXIDE ALKALINITY - (OH)-,
CARBONATE ALKALINITY - (CO3), NO BICARBONATES
Note: HCO3 and OH cannot exist together in the same solution. 12.0
- (HCO3)-, NO CARBON DIOXIDE- CO2

If the assumption is made that HCO3 is present, then the following 11.0
10.0
is true: PINK 9.4
a) MO = HCO3 + CO3
b) P = ½ CO3
CARBONATE (CO3) AND BICARBONATE ALKALINITY
To determine the HCO3 concentration double equation b) and sub- 9.0 (HCO3)-, NO FREE CARBON
DIOXIDE CO2 NO CAUSTIC ALKALINITY (OH)
tract from equation a): MO - 2P = HCO3. 8.3
COLORLESS
The CO3 concentration is b) doubled: 2P = CO3. 8.0

If the assumption is made that OH is present, then from our basic


equations 1., and 2., the following is true: NEUTRALITY 7.0
6.0 BICARBONATE ALKALINITY (HCO3)-, AND FREE
a) MO = CO3 + OH 5.0 CARBON DIOXIDE CO2, NO CARBONATE ALKALINITY
b) P = ½ CO3 + OH (CO3) =

To determine CO3, subtract equation b) from a) and double the


ORANGE 4.4
result: 2 (MO-P) = CO3. 4.0
METHYL
To determine OH, double equation b) and subtract a) from ORANGE
b): 2P - MO = OH. INDICATOR
RANGE MINERAL ACIDS
If the assumption has been made that HCO3 (or OH) is present and RED 3.1 H2SO4, -HC1, -HNO3.
the equations result in negative numbers, then the assumption is 2.0
incorrect and the other equations should be used. 1.0
0.0

160 Cooper Road • West Berlin, NJ 08091 USA • p: 856.768.9600 • f: 856.768.9601• e: ixresin@resintech.com • w: resintech.com

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