Determination of Alkalinity: Gargi Memorial Institute of Technology
Determination of Alkalinity: Gargi Memorial Institute of Technology
Determination of Alkalinity: Gargi Memorial Institute of Technology
DETERMINATION OF ALKALINITY
OBJECTIVE: To determine the various forms of alkalinity present in a given sample of water.
INTRODUCTION: The alkalinity of water is a measure of its capacity to neutralize acids. The major
portion of the alkalinity in natural waters is caused by hydroxide, carbonate and bicarbonate, and
thus the alkalinity is taken as an indication of the concentration of these constituents. Alkalinity
values provide guidance in applying proper doses of chemicals in water and wastewater treatment
processes, particularly in coagulation, softening and operational control of anaerobic digestion.
SELECTION OF THE METHOD: There are three procedures for the measurements of various forms of
alkalinity present in water, this are-
The first procedure is simple and does not involve knowledge of fundamental chemistry. Hence this
method will be followed. This is to be noted that the procedure is approximate for samples with pH
greater than 9, for accuracy in such a case the second or third procedure may be followed.
REAGENTS:
1. Carbon dioxide free distilled water: Prepare all stock and standard, and dilution water for
the standardization procedure, with distilled water which has a pH not less than 6.0 if the
water has a lower pH, it should be freshly boiled for 15 min and cooled to room
temperature.
2. Standard sulphuric acid (H2SO4) titrant, 0.02N: Prepare stock solutions of 0.1N strength
(Approximately) by diluting 2.8 ml concentrated H2SO4 to 1 liter. Dilute 200 ml of the 0.1N
stock solution to 1 liter with CO2 free distilled water. It is to be standardized against 0.02N
sodium carbonate (Na2CO3) solution which has been prepared by dissolving 1.06o g
anhydrous Na2CO3 oven dried at 140°C, and diluting to the mark of a 1 liter volumetric flask.
3. Phenolphthalein indicator solution.
4. Methyl orange indicator solution.
5. 0.1N sodium thiosulfate solution: Dissolve 25 g Na2S2O3.5H2O and dilute to 1 liter with
distilled water.
PROCEDURE:
A X N X 50000
Phenolphthalein alkalinity as mg/l of CaCO 3 =
ml of sample
B X N X 50000
Total alkalinity as mg/l of CaCO3 =
ml of sample
A = ml of H2SO4 titrant for sample to reach the Phenolphthalein end point or bring
the pH to 8.3.
B= ml of H2SO4 titrant for sample to reach the Methyl orange end point or bring the
pH to 4.5.
N = Normality of acid.