Alkalinity of water is essential parameter to be found before its consumption. Following is a self explanatory presentation of why it is important and how to find the same in any sample of water.

1. ALKALINITY TEST OF WATER
• It is the Acid Neutralizing property of water
•Caused due to presence of OH, CO3 & HCO3 ions
•Is analyzed by volumetric method by,
•Using Phenolphthalien & Methyl Orange indicators
•The principle behind this is mere chemical reaction,
•Between H+ and OH– ions
• It is to be noted that this is independent of pH
Theory / Principle

2. • The presence of OH ions occurs at pH 8.5 or
above whereas CO3 ions occur at pH ranges
between 6.5 to 8.5 and lastly bicarbonate ions
ie. HCO3 occur when the pH falls down to 4.5
from 6.5.
• The reaction of acid and a base always result
in neutralizing pH to a scale of 7 and thus in
order to determine the Alkalinity of any water
body an acid is used for neutralizing OH, CO3
& HCO3 ions to H2O and CO2 respectively

3. Procedure
• Take 100mL sample in a 250mL capacity conical
flask
• In a burette take N/50 H2SO4 solution
• To the sample containing flask add 4-5 drops of
Phenolphthalien indicator
• Pink color indicating presence of OH and CO3
ions will appear

4. • Now titrate the sample against H2SO4 till the
pink color disappears (colorless) (in this OH
combines with H and gets converted to H2O
and CO3 gets converted to HCO3)
• Note the value of N/50 H2SO4 consumed for
the color change of the sample as “P” or the
phenolphthalien end point.
• Now to the same sample add 1 drop of Methyl
Orange indicator

5. • Pale yellow color indicating the presence of
HCO3 ions will appear
• Now without filling the burette again start the
titration from the same end point “P” till the
color changes to light orange (in this the HCO3
ions gets converted to H2O and CO2 by
reacting with H+ ions of the acid)
• Note down the final value of N/50 H2SO4
consumed to complete the analysis of
alkalinity as “T”

6. • Repeat the whole experiment for finding the
concordant value of the acid consumed for
neutralizing the sample of water
• Using the equation –
N1V1 = N2V2
We have to find out the amount of Alkalinity causing
ions present in water either in mg/L or in p p m
(parts per million)
Calculations

7. 1. Phenolphthalien end point –
Vol. of H2SO4 used is “P” and is said to be V2 where
its normality is known as to be N2 ie. 1/50
By this the value of N1 or the concentration of
alkalinity causing ions can be found by implying the
formula –
N1 = N2V2/V1 = 1 X P = OH + CO3 alkalinity
50 X 100
In simpler way it can be taken as –
OH + CO3 Alkalinity = P X 1000 or P X 10 mg/L
100

8. 2. Methyl orange / Total end point –
Vol. of H2SO4 used is “T” and is said to be V2 where
its normality is known as to be N2 ie. 1/50
By this the value of N1 or the concentration of
alkalinity causing ions can be found by implying the
formula –
N1 = N2V2/V1 = 1 X T = HCO3 alkalinity in mg/L
50 X 100
In simpler way it can be taken as –
OH + CO3 Alkalinity = T X 1000 or T X 10 mg/L
100

9. • Results are further interpreted by using the
below table
Values of P& T OH CO3 HCO3
P = T T 0 0
P = T / 2 0 2 P 0
P < T / 2 0 2 P T – 2 P
P > T / 2 2 P - T 2 (T – P) 0
P = 0 0 0 T

10. VIVA QUESTIONS
• Q. (1) why a given water sample can not be alkaline due to
the simultaneous presence of OH- and HCO3
-?
• Q. (2) What do you mean by the alkalinity of the water
sample?
• Q. (3) What are the drawbacks of the high alkalinity of the
water ?
• Q. (4) How you will conclude that the given water sample is
alkaline due to simultaneous presence of OH- and HCO3
-?
• Q.(5) How the alkalinity data are useful in environmental
engineering Practice?
• Q.(6) Why the pH of pond water is high? What type of
alkalinity would be present?