Env.

Analytical Chemistry
ENV-302

Prepared by: Dr.Aamir Alamgir

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• Introduction
Agenda • Requirements
• Procedure
• Calculations
• Principle
• Environmental Effects
• Numerical Analysis
• Question / Answer
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Estimation of ALKALINITY in water

(Acid Base Titration Method)
Dr. Aamir Alamgir
IES,UoK
 Dr. Aamir Alamgir 4

Introduction
• The capacity of water to neutralize a strong acid
is regarded as total alkalinity.
• It is characterized by the presence of all hydroxyl
ions capable of combining with the hydrogen
ions.
• The alkalinity of water is due to the presence of
salts of carbonates, bicarbonates, phosphates,
nitrates and borates together with the hydroxyl
ions in free state.
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Introduction

• When a salt of weak acid and strong base is

hydrolyzed, a weak acid and strong base is
formed.
• This weak acid cannot be dissociated further and
the equilibrium is shifted to the right and all the
salt is hydrolyzed upon titration with strong acid.
• The milliequivalent of acid used to combine all
the hydroxyl ions represents total alkalinity.
• Total Alkalinity = HCO3– + 2CO3–2 + OH– + H–
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INTERFERENCES

• Sample colour and turbidity interfere with the

end point of titration

• SAMPLE SIZE

• 50 ml or any portion diluted upto 50 ml

• PRESERVATION

• Sample can be kept in plastic or glass containers and

stored at 4C.
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Preservation

• Sample can be kept in plastic or glass containers and

stored at 4 degree Celsius.

SAMPLE SIZE

• 50 ml or any portion diluted upto 50 ml

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REQUIREMENTS
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Requirements
• Sulphuric acid (0.1 N)
Dilute 3.0 ml conc. H2SO4 to 1 liter with distilled
water and standardize with 0.1 N Na2CO3

• Phenolphthalein Solution, Alcoholic, pH 8.3 indicator

Dissolve 0.5 gm of phenolphthalein in 50 ml 95% ethanol
then add 50 ml of distilled water. Add 0.05 N NaOH
solution till it becomes faintly pink.
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Requirements
• Methyl Orange Indicator
Dissolve 1 gm of methyl orange in 1 litre of water. Filter, if
necessary.

• Sodium carbonate (0.1 N)

Dissolve 5.3 gm of Na2CO3 anhydrous in distilled water
and dilute to 1 litre
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Procedure
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FLOW SHEET
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CALCULATIONS
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Calculations
A × N × 50,000
• Phenolphthalein Alkalinity, mg CaCO3/L = --------------------------
Sample volume (ml)

B × N × 50,000
• Total Alkalinity, mg CaCO3/L = ----------------------------
Sample volume (ml)

Where,
• A = ml of H2SO4 used with phenolphthalein (pH 8.3)
• B = ml of H2SO4 used with phenolphthalein and methyl orange
(pH 4.5)
• N = Normality of the acid= 0.1 N
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Calculations
Concentration of carbonates, bicarbonates and hydroxyl
ions can be determined from the table using the following
equation.
CO3–2 HCO3–
Result of OH– alkalinity
alkalinity as alkalinity as
titration as CaCO3
CaCO3 CaCO3
P=0 0 0 T

P<½T 0 2P T – 2P

P=½T 0 2P 0

P>½T 2P – T 2(T – P) 0

P=T T 0 0
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PRINCIPLE
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Principle
The phenolphthalein alkalinity and the total
alkalinity are determined by titration of an
unfiltered/filtered sample aliquot with a standard
solution of strong acid to pH 8.3 and 4.5,
respectively. They are expressed as mg/L CaCO3.
Phenolphthalein or metacresol purple may be used
for alkalinity titration at pH 8.3. Bromocresol
green, methyl orange, or a mixed bromocresol
green-methyl red indicator may be used for pH 4.5
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Principle
The various alkalinities are estimated by titrating
the water sample against a standard acid using
phenolphthalein and methyl orange indicators
successively.
Hydroxide ions is completely neutralized to water
using phenolphthalein
indicator (single step neutralization)
OH- + H+ H 2O
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Principle
Carbonate ions is neutralized to bicarbonate ions
using phenolphthalein indicator in the first step.
In the second step, these bicarbonate ions is
completely neutralized to water and carbon
dioxide using methyl orange indicator
(double step neutralization).
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Principle
• Bicarbonate ions is completely neutralized to
water and carbon dioxide using methyl orange
indicator (single step neutralization).
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ENVIRONMENTAL EFFECTS
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Environmental Effects
• Alkalinity is not harmful to human being. It is important
for calculating dose of alum and biocides.
• Alkalinity producing substances such as sodium
bicarbonate are added to check corrosion in soft water
supplies.
• It is also important in controlling water and wastewater
treatment processes.
• All the carbonates and bicarbonates are converted to
carbonic acid at pH 3.65, therefore in determination of
total alkalinity a suitable indicator changing colour at this
pH is required. Methyl orange is most appropriate
indicator changing its colour at this pH.
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QUESTIONS/ ANSWERS
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Answer the following

1. What is P alkalinity?
2. What is M alkalinity?
3. Differentiate between P and M alkalinity.
4. How alkalinity develops in natural waters?
5. What is the role of strong acid in the reaction?