Generally hardness of water is defined as the measure of capacity of water to precipitate soap i.e., the capacity of the water to form lather with soap. Hard water contains dissolved minerals such as Ca2+, Mg2+, Fe3+, SO4 2- ,etc., The degree of hardness is measured in Parts Per Million(ppm) or Grams per Gallon(GPG). Hard water is better for drinking because it contains minerals. Soft water is better for cleaning because it doesn’t form scum with soap. Hardness of water is a measure of the total concentration of the calcium and magnesium ions expressed as calcium carbonate. There are two types of hardness 1. Temporary hardness Temporary Hardness is due to the presence of bicarbonates of calcium and magnesium. It can be easily removed by boiling. Ca (HCO3 ) CaCO3 +CO2 +H2O 2. Permanent hardness Permanent Hardness is due to the presence of chlorides and sulphates of calcium and magnesium. This type of hardness cannot be removed by boiling.

1. Hardness of Water
JOMSON MATHACHAN
ROLL NO: 60
S7 CHEMICAL ENGINEERING
GEC KOZHIKODE

2. Generally hardness of water is defined as the measure
of capacity of water to precipitate soap i.e., the capacity
of the water to form lather with soap.
Hard water contains dissolved minerals such as Ca2+,
Mg2+, Fe3+, SO4 2- ,etc.,
The degree of hardness is measured in Parts Per
Million(ppm) or Grams per Gallon(GPG).
Hard water is better for drinking because it contains
minerals.
Soft water is better for cleaning because it doesn’t form
scum with soap.

3. • Hardness of water is a measure of the total
concentration of the calcium and magnesium ions
expressed as calcium carbonate.
• There are two types of hardness
1. Temporary hardness
Temporary Hardness is due to the presence of
bicarbonates of calcium and magnesium. It can be
easily removed by boiling.
Ca (HCO3 ) CaCO3 +CO2 +H2O
2. Permanent hardness
Permanent Hardness is due to the presence of
chlorides and sulphates of calcium and magnesium.
This type of hardness cannot be removed by boiling.

4. • The hardness of water can be estimated by methods such as
1. Water Hardness Meter
2. Gravimetric analysis
It will determine by analyzing the calcium chloride
content and comparing that content to a water hardness
scale. To accomplish this, gravimetric technique will be
performed for a standard solution containing calcium
chloride and the results will be used to analyze the tap
water, containing an unknown amount of calcium
chloride.

5. 3. EDTA titration
• EDTA titration is the most inexpensive and simple way
of determining the hardness.
• Ca2+ and Mg2+ ions along with other metal ions such
as Fe3+ and Pb2+ can be removed from hard water by
the addition of EDTA
• EDTA has a greater affinity for Ca2+ and Mg2+ when it
is in the form of the dihydrogen anion H2EDTA2- . This
is the ionic form of EDTA at pH 10
Reagents
1. Buffer (pH 10): mixture of ammonia and ammonium
chloride solutions in water.
2. EDTA (Disodium Salt of EDTA) for precise end point.
3. Erichrome Black T.

6.  Permanent hardness is usually determined by
titrating it with a standard solution of
ethylenediamminetetraacetic acid, EDTA.
 The EDTA is a complexing, or chelating agent used
to capture the metal ions. This causes the water to
become softened, but the metal ions are not removed
from the water.
 This method includes a series of titrations to
determine the total, permanent, temporary, Ca, Mg
hardness of the given water sample.
 First the EDTA soln. is standardized by titrating it
against a standard CACl2 solution and its normality is
found out. End point is appearance of steel blue color.

7.  Then the total hardness is found out by titrating the
water sample(added buffer solution and EBT
indicator) against the standardized EDTA solution
with end point as the same steel blue color.
Hardness=N x 50 x 1000 (N-Normality)
 The permanent hardness is found out by titrating a
boiled and filtered hard water sample against EDTA
solution
 Temporary hardness is found by subtracting the
permanent hardness from the total hardness.
 The Ca hardness is found by titrating the water
sample(added 2N NaOH, murexide indicator) against
EDTA solution. Here the end point is the appearance
of purple color. If necessary the Mg hardness is found
by subtracting the Ca hardness from total hardness.

8. ADVANTAGES:
 It is a very simple and fairly accurate method.
 It also very cost efficient as only a burette and a conical
flask are required.
 It also very quick and time efficient process when
compared to gravimetric analysis.
DISADVANTAGES
 A disadvantage is that there might be some human errors
due to the solutions made up by hand.
 EDTA grabs all the metal ions in the water, not just the
Ca2+ ions. This gives us a value that is not truly the
concentration of Ca2+ ions. This causes an experimental
error of about 1%, but that is acceptable.