Hardness of
water

Applied Chemistry
LEARNING TARGETS
 Basics of water
 Sources of water
 Impurities in water
 Effect of impurities
 Alkalinity of water
 Hardness of water

Applied Chemistry
 Troubleshooting due to hard water
Boiler corrosion, causes and prevention
Caustic imbrittleness , causes and prevention
 Softening of water
Soda lime process
Zeolite
Ion exchanger
 Water treatment for municipal water supply

Applied Chemistry
Basics of water
“A clear transparent liquid,
perfectly neutral in reaction
and devoid of taste or smell”
In the pure state it is composed of
oxygen and hydrogen in proportion of
1:2 by volume

Applied Chemistry
Concept of pure water
“Water that is free from objectionable
color, odor, taste & turbidity is called pure
water”
“Pure water which contains adequate amount
of dissolved oxygen but no microorganisms
and other organic pollutants and is free of
microbial and chemical toxins is called
wholesome water”
Pure water
Wholesome water

Applied Chemistry
Key H2O Characteristics
• Water is clear, transparent, tasteless liquid at ordinary temp. in the pure
state.
• It is prime constituent of all living organisms.
• Water moves easily from one physical state to another, and from one
place to another.
• Its specific gravity is 1
• It is bad conductor of heat and electricity
• It expands on heating and at 1000c it gives invisible vapors at 1 atm.
pressure
• On cooling it contracts till 40c
• It has maximum density at 40c
• Further lowering of temperature, it further contracts and solidify at 00c
• Water slowly absorbs and releases large quantities of energy.
• Water is a superior solvent and solubalise many solute at low or
elevated temp
• It liberates heat when H2SO4 or HCl is added to it.
• NH4Cl, NH4SCN, NaNO2 is added to it.

Applied Chemistry

Applied Chemistry
How much water is available ?

Applied Chemistry
•It is a universal solvent.
•It is an efficient transport medium (nutrients)
•Facilitates thermoregulation in body.
•Helps in maintenance of blood and plasma volume –cellular osmotic
pressure.
•Assist in secretary and excretory functions of body–constituent of
enzyme & hormonal secretions.
•Valuable medium for administration of therapeutics.
•Helps in propagating useful aquatic flora and fauna.
•Essential for irrigation, power generation & domestic purpose.
Functions of Water

Applied Chemistry
• Industrial growth & development has increased the sewage
production.
• Increased flow of sewage and organic matter has increased the BOD
from 1 mg/liter (for neutral waters) to 300-500 mg/liter (polluted
water).
• Micro-organisms present in farm and domestic effluents are added to
fresh water sources (rivers & lakes).
• Dissolved salts can make water hard and unpalatable
• Industrial wastes rich in intermediate products & heavy metals, etc are
added to river streams.
Need for water purification

Applied Chemistry
•To remove color, objectionable odor and taste.
•To remove dissolved gases and suspended solids.
•To remove suspended and dissolved organic solids.
•To remove pathogenic bacteria.
•To make water safe for industrial, drinking and domestic purpose.
Objectives of Water Purification

Applied Chemistry
Sources
Rain water Surface water
Sea Water
Lakes and ponds
Stream and riverGround water
Sources of water

Applied Chemistry

1. Suspended impurities
Clay, sand, Vegetable matter etc.
2. Dissolved impurities
Bicarbonate, Chloride, Sulfate of Ca and Mg
Dissolved O2, CO2, H2S
3. Colloidal impurities
Fe(OH)3, Al(OH)3
4. Biological impurities
Impurities in water

Applied Chemistry
Effect of impurities
1. Imparts color
2 Impart odor
3. Impart Taste
4. Impart Turbidity
5. Impart Alkalinity
6. Impart Hardness
Minerals

It is mainly due to
1. Only hydroxide (OH-)
2. Only carbonate (CO3
- -)
3. Only Bicarbonate (HCO3
- )
4. Both hydroxide (OH-)and carbonate (CO3
- -)
5. Both carbonate (CO3
- -)and bicarbonate (HCO3
- )
6. But not due to hydroxide (OH-) and (HCO3
- )
Alkalinity of water
OH- + HCO3
-
H2O + CO2

Methods of determination of alkalinity of water
Water Sample
Phenolphthaline
Pink color
Phenolphthalein end point (colorless) (P)
Methyl orange indicator
Yellow
Methyl orange end point (red color) (M)

1. Temporary hardness
 It is due to bicarbonate of calcium and magnesium
 It is removed by boiling
Boil
soluble In soluble
Ca (HCO3)2 CaCO3 + H2O + CO2
Mg (HCO3)2 MgCO3 + H2O + CO2
soluble In soluble
Boil
Hardness of water

 It is due to chloride and sulfate of calcium and magnesium
 It is not removed by boiling
2. Permanent hardness

Methods of determination of hardness of water
1. Soap titration method.
When soap is added to water, it combines with hardness producing
impurities to form insoluble compounds and do not produce lather.
Further addition of soap solution produces lather
2 C17H35COONa + CaSO4 (C17H35COO)2 Ca + Na2SO4
2 C17H35COONa + CaCl2 (C17H35COO)2 Ca + NaCl
2 C17H35COONa + MgSO4 (C17H35COO)2 Mg + Na2SO4
2 C17H35COONa + MgCl2 (C17H35COO)2 Mg + NaCl
2 C17H35COONa + Ca(HCO3)2 (C17H35COO)2 Ca + NaHCO3
2 C17H35COONa + Mg(HCO3)2 (C17H35COO)2 Mg + NaHCO3

2. EDTA method
Structure of EDTA
CH2CH2 NN
CH2COOH
CH2COOH
HOOCCH2
HOOCCH2
CH2CH2 NN
OOCH2C
CH2COOHCH2COOH
CH2COO M
Structure of Metal EDTA complex

Applied Chemistry
Units of Hardness
Hardness of water is express in CaCO3 equivalent
For conversion of any salt into its CaCo3 Equivalent it is multiplied by
a multiplication number
CaCO3 equivalent of salt = Wt of salt x M. W. of CaCO3 / M. W. salt