This document provides instructions for estimating the alkalinity of river and borewell water samples. It defines alkalinity as the ability of water to neutralize acids and lists the main ions responsible. The procedure involves titrating water samples against a standardized hydrochloric acid solution using phenolphthalein and methyl orange indicators to determine the concentrations of hydroxide, carbonate, and bicarbonate ions present. The end points of each indicator are noted and alkalinity values calculated based on the titration volumes and a reference table provided. The type and amounts of alkalinity ions determined for each water sample are to be reported as the results.

1. DEPARTMENT OF CHEMISTRY
22CYL11 – Chemistry Laboratory for
Electrical Systems
B.E - EIE
Prepared By
V N Kowshalya
Assistant Professor (SRG)
Department of Chemistry
Kongu Engineering College,
Perundurai, Erode-638060
Estimation of Alkalinity of River and
Borewell water Collected from Places

2. Estimation of Alkalinity of River and
Borewell water Collected from Places
 Alkalinity – Ability of the water to neutralize the acid
(or) Acid consuming capacity of water
 Ions responsible for alkalinity
(i) Hydroxide ions (OH-) only (ii) Carbonate ions (CO3
2-) only
(iii) Bicarbonate ions (HCO3
-) only
(iv) Hydroxide ions (OH-) & Carbonate ions (CO3
2-)
(v) Carbonate ions (CO3
2-) & Bicarbonate ions (HCO3
-)
 Types of alkalinity
 Based on anions present in water alkalinity can be classified into three types
Hydroxide alkalinity due to the presence of OH- ions
Carbonate alkalinity due to the presence of CO3
2- ions
Bicarbonate alkalinity due to the presence of HCO3
- ions

3. Alkalinity in water analysis
In water analysis it is often desirable to know the kinds and amounts of the various types of
alkalinity present in water.
 For that we are using two indicators in same titration (Titration - II)
The water sample which is to be analyzed is titrating against standard acid (HCl, HNO3 or H2SO4)
using phenolphthalein & methyl orange indicator
 pH range of phenolphthalein indicator  8.0 – 9.0
End Point : Disappearance of pink colour (phenolphthalein indicator)
 pH range of methyl orange indicator  4.5 – 5.5
End Point : Colour changes from yellow to reddish orange (methyl orange indicator)
Principle:
1. OH- + H+  H2O  Phenolphthalein
2. CO3
2- + H+  HCO3
-
3. HCO3
- + H+  H2O + CO2  Methyl Orange

4. All the three ions cannot exists together. OH- and HCO3
- cannot be present at the same
time together, because
OH- + HCO3
- → CO3
2- + H2O
Ex: NaOH + NaHCO3 → Na2CO3 + H2O

5. Short Procedure
Standardization of Hydrochloric Acid
(Standard Sodium hydroxide Vs Unknown Hydrochloric acid
Burette Solution: Unknown HCl
Pipette Solution : 20 ml of Standard NaOH
Reagents to be added : Nil
Condition : Room Temp.
Indicator : 2 drops of phenolphthalein
End Point : Disappearance of pink colour
Standard
NaOH
Standard NaOH
+
Phenolphthalein
Disapperance
of pink colour

7. Estimation of Alkalinity
(Standardized HCl Vs Given Water Sample
Burette Solution : Standardized HCl
Pipette Solution : 20 ml of given water sample
Reagents to be added : Nil
Condition : Room Temp.
Indicator : 2 drops of Phenolphthalein &
2 drops of Methyl Orange
End Point : Disappearance of pink colour (V1 ml) &
Colour changes from yellow to reddish orange (V2 ml)
Water
sample
Water sample
+
Phenolphthalein
Disappearance of
pink colour
After
disappearance of
pink colour +
Methyl orange
Colour
changes from
yellow to
reddish orange

9. Alkalinity OH- (ppm) CO3
2- (ppm) HCO3
- (ppm)
P=0 0 0 M
P=1/2M 0 2P 0
P<1/2 M 0 2P (M-2P)
P>1/2 M (2P-M) 2(M-P) 0
P=M M 0 0
Reference Table

10. Result:
1. The type of alkalinity present in the river/bore well water sample =
2. The individual amounts of alkalinity present in the river/borewell water sample =
a) ---------- = ----------- PPM
b) ---------- = ----------- PPM

11. VIVA - VOCE QUESTIONS
1. What is alkalinity?
2. Write the ions responsible for alkalinity.
3. Name the indicators used in the experiment.
4. Write the pH range of phenolphthalein and methyl orange indicator.
5. Why a water sample does not contain all the three ions together?
6. Why we are adding two indicators in the titration-II?
7. Name the salts which causes alkalinity.
8. What is the end point for phenolphthalein and methyl orange indicator?
9. When P=0, P=M, P=1/2M, P<1/2M, P<1/2M, alkalinity of water sample is due to the
presence of which ions?

12. REFERENCES:
 1.Palanisamy P.N., Manikandan P., Geetha A.& Manjula Rani K,
“Chemistry lab Manual”, 2023.
2-Aug-23

13. 2-Aug-23
THANK
YOU
THANKYOU