This document provides a procedure for determining the alkalinity of water samples. Alkalinity is measured through acid-base titration and is important as it indicates a water sample's ability to resist changes in pH. The procedure involves titrating the sample with sulfuric acid using phenolphthalein and methyl orange indicators. The titrations are used to determine the phenolphthalein alkalinity and total alkalinity in mg/L of calcium carbonate. For the given water sample, the phenolphthalein alkalinity was found to be 0 while the total alkalinity was determined to be 65 mg/L, within the recommended limit of less than 200 mg/L.

1. AIM: DETERMINE ALKALINITY (BY VISUAL TITRATION)
Introduction
The alkalinity of water may be defined as its capacity to neutralize acid, that is, the ability to maintain a
relatively constant pH. Alkalinity of water may be due to the presence of one or more of a number
of ions. These include hydroxides, carbonates and bicarbonates. Alkalinity is important because
it buffers against rapid pH changes. However, large amount of alkalinity imparts bitter taste in
water.
Principle
Alkalinity is determined by titration of the sample with a standard solution of a mineral acid.
Sulphuric acid of known concentration is used. When titrated with acid, the OH-
, CO3
2-
and
HCO3
-
ions will be neutralized.
Reagents to be used:
a) Sodium carbonate solution, 0.05 mol L-1
b) Sulphuric acid, 0.05 mol L-1
c) Phenolphthalein indicator
d) Methyl orange indicator
Apparatus
a) Conical flask
b) Burette
c) Measuring Cylinder
d) Volumetric pipette and pipette pump
e) Beakers

2. Procedure
Part 1: Titration using Phenolphthalein Indicator
Standardization of Sulphuric Acid (to chek molarity of acid)
a) The burette is tightly clamped and using a burette funnel, the burette is filled with
sulphuric acid till about the 0 mark. The funnel is removed and the burette tap is opened
so as to adjust the sulphuric acid at the 0 mark and to remove air bubbles in the burette.
b) 25 ml of sodium carbonate solution is transferred to a conical flask with a 25 ml
volumetric pipette and 20 ml of distilled water is added to it.
c) 2 or 3 drops of phenolphthalein indicator is added to the conical flask and swirled. The
solution turns pink.
d) A piece of white paper is placed under the conical flask before starting the titration so
that colour change is easily seen.
e) The initial burette reading is recorded.
f) The Sodium Carbonate is then titrated with sulphuric acid until the pink colour
disappears.
g) The final burette reading is then recorded.
h) The titration is again repeated so as to obtain a more accurate titration value.
Titration No. 1 2
Final burette reading/ cm3
28.60 28.60
Initial burette reading/ cm3
0.00 0.00
Volume required/ cm3
28.60 28.60
The above procedure is then repeated using the sample of water. However, on addition of 2 or 3
drops of phenolphthalein indicator, no colour change was observed. Hence we can conclude that
phenolphthalein alkalinity is 0.

3. Part 2: Titration using Methyl Orange indicator
a) The burette is tightly clamped and using a burette funnel, the burette is filled with
sulphuric acid till about the 0 mark. The funnel is removed and the burette tap is opened
so as to adjust the sulphuric acid at the 0 mark and to remove air bubbles in the burette.
b) 100 ml of sample is placed in a conical flask and is mixed with a few drops of methyl
orange indicator. The sample turns yellow.
c) The initial burette reading is recorded.
d) The sample is then titrated with the acid until the first perceptible colour change towards
orange take place.
e) The final burette reading is then recorded.
f) The titration is again repeated so as to obtain a more accurate value.

4. Titration No. 1 2
Final burette reading/ cm3
1.30 1.30
Initial burette reading/ cm3
0.00 0.00
Volume required/ cm3
1.30 1.30
Calculations
Phenolphthalein alkalinity (as CaCO3) = (A × M × 105
) / V mg/L
Where A = volume of standard acid solution (mL) to reach the phenolphthalein end point
M = concentration of acid (mol/L)
V = volume of sample (mL)
The Phenolphthalein alkalinity is 0 since there is no colour produced.
Phenolphthalein alkalinity (as CaCO3) = 0
Total alkalinity (as CaCO3 ) = B x M x 105
) / V mg/L
Where B = Volume of standard acid solution (ml) to reach methyl orange end point
M = concentration of acid (mol/L)
V = volume of sample (mL)
Therefore, total alkalinity (as CaCO3) = (1.30 x 0.05 x 105
) / 100
= 65 mg/L
Conclusion
According to the WHO guidelines the alkalinity should be <200 mg/L, thus 65 mg/L lies within
the said range.
Precautions
The following precautions should be observed while performing the experiment:
a) Do not keep the indicator solution open since it contains the alcohol which tends to evaporate.
b) Care should be taken while handling acids. If in contact with skin, it should be immediately
washed under running water.