CAN ACADE
TT MY
Bhatti Street Near Mann–o–Salwa Tulsa Road Lalazar Rwp Ph: 051-8442595, WE OWN OUR STUDENTS
5122139, Cell: 0345-5930370
CHAPTER-NO-15: ENVIRONMENTAL CHEMISTRY – II
WATER HARD WATER:
Water that gives little lather or form scum with soap is called hard water.
SOFT WATER:
Water that easily gives latter with soap and does not from scum is called soft water.
CAUSES OF WATER:
Rain water dissolve carbon-dioxide from air. This carbon-dioxide reacts with water to produce
carbonic acid. H2O + CO2 ⇋ H2CO3
When this carbonic acid (carbonated water) passes through the rocks containing calcium
carbonate or magnesium carbonate then calcium and magnesium hydrogen carbonates are
formed. These hydrogen carbonates causes hardness in water.
H2CO3 + CaCO3 Ca(HCO3)2
H2CO3 + MgCO3 Mg(HCO3)2
TYPES OF HARDNESS:
There are two types of hardness of water.
1) Temporary Hardness 2) Permanent Hardness
1) TEMPORARY HARDNESS:
Such hardness of water which can be easily removed by boiling the water is called temporary
hardness. Temporary hardness is caused by calcium and magnesium hydrogen carbonates.
These hydrogen carbonates dissolve in water and cause temporary hardness.
2) PERMANENT HARDNESS:
Such hardness of water which cannot be removed by boiling the water is called permanent
hardness. Permanent hardness is caused by sulphates and chlorides of calcium and magnesium.
These sulphates and chlorides dissolve in water and cause permanent hardness.
METHODS TO REMOVE TEMPORARY HARDNESS:
Two methods are used to remove temporary hardness.
1) Boiling Method 2) Clark’s Method
1) BOILING METHOD: Temporary hardness of water can be removed by boiling the water.
During boiling, the soluble calcium and magnesium hydrogen carbonates are decomposed and
as a result insoluble carbonated are formed. These insoluble carbonates are removed from water
easily. Therefore after removal of insoluble carbonates water becomes soft.
Ca (HCO3)2 CaCO3 + CO2 + H2O
Mg (HCO3)2 MgCO3 + CO2 + H2O
, CAN ACADE
TT MY
Bhatti Street Near Mann–o–Salwa Tulsa Road Lalazar Rwp Ph: 051-8442595, WE OWN OUR STUDENTS
5122139, Cell: 0345-5930370
CLARK’S METHOD: Temporary hardness of water can be removed on the large scale by us-
ing Clark’s method. According to this method an estimated amount of slaked lime Ca (OH)2 is
added in hard water. The slaked lime reacts with hydrogen carbonated and form insoluble car-
bonates. These insoluble carbonates are allowed to settle down at the bottom and soft water is
collected from the top. Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O
Mg(HCO3)2 + Ca(OH)2 CaCO3 + MgCO3 + 2H2O
METHOD TO REMOVE PERMANENT HARDNESS:
Two methods are used to remove permanent hardness of water.
1) By adding washing soda 2) By ion exchange method
1) BY ADDING WASHING SODA: On the large scale permanent hardness of water can be
removed by adding washing soda (Na2CO3. 10H2O). As a result of this washing soda calcium
(Ca+2) and magnesium (Mg+2) ions are removed and produce insoluble carbonates. These insol-
uble carbonates settle down at the bottom and soft water is separated from top.
Ca+2 + C𝑂−2 CaCO3
3
Mg+2 + C𝑂−2
3
MgCO3
2) ION EXCHANGE METHOD:
On the large scale ion exchange method is used to remove permanent hardness of water. In this
method the hard water is passed through a container filled with a suitable resin containing
sodium ions. For this purpose a special sodium ion is used which is known as sodium zeolite.
Sodium zeolite is natural ion exchanger. It is written as Na2Z. This sodium zeolite exchange
Calcium (Ca+2) and magnesium (Mg+2) ions which cause hardness. Sodium zeolite is
chemically known as sodium aluminum silicate.
Ca+2 + Na2Z 2Na+ + CaZ
Mg+2 + Na2Z 2Na+ + MgZ
The ion exchange method is very economical method because the zeolite ions can be
regenerated by heating with concentrated solution of NaCl.
CaZ + 2NaCl Na2Z + CaCl2
DISADVANTAGE OF HARD WATER:
i) Hard water wastes large amount of soap when it is used for washing.
ii) The soap forms scum with hard water. This scum can spoil the finish of some fabrics.
iii) Hard water form insoluble calcium and magnesium salts. These salts can block car
radiators, boilers and hot water pipes.
iv) Hard water can cause kettles to fur.
TT MY
Bhatti Street Near Mann–o–Salwa Tulsa Road Lalazar Rwp Ph: 051-8442595, WE OWN OUR STUDENTS
5122139, Cell: 0345-5930370
CHAPTER-NO-15: ENVIRONMENTAL CHEMISTRY – II
WATER HARD WATER:
Water that gives little lather or form scum with soap is called hard water.
SOFT WATER:
Water that easily gives latter with soap and does not from scum is called soft water.
CAUSES OF WATER:
Rain water dissolve carbon-dioxide from air. This carbon-dioxide reacts with water to produce
carbonic acid. H2O + CO2 ⇋ H2CO3
When this carbonic acid (carbonated water) passes through the rocks containing calcium
carbonate or magnesium carbonate then calcium and magnesium hydrogen carbonates are
formed. These hydrogen carbonates causes hardness in water.
H2CO3 + CaCO3 Ca(HCO3)2
H2CO3 + MgCO3 Mg(HCO3)2
TYPES OF HARDNESS:
There are two types of hardness of water.
1) Temporary Hardness 2) Permanent Hardness
1) TEMPORARY HARDNESS:
Such hardness of water which can be easily removed by boiling the water is called temporary
hardness. Temporary hardness is caused by calcium and magnesium hydrogen carbonates.
These hydrogen carbonates dissolve in water and cause temporary hardness.
2) PERMANENT HARDNESS:
Such hardness of water which cannot be removed by boiling the water is called permanent
hardness. Permanent hardness is caused by sulphates and chlorides of calcium and magnesium.
These sulphates and chlorides dissolve in water and cause permanent hardness.
METHODS TO REMOVE TEMPORARY HARDNESS:
Two methods are used to remove temporary hardness.
1) Boiling Method 2) Clark’s Method
1) BOILING METHOD: Temporary hardness of water can be removed by boiling the water.
During boiling, the soluble calcium and magnesium hydrogen carbonates are decomposed and
as a result insoluble carbonated are formed. These insoluble carbonates are removed from water
easily. Therefore after removal of insoluble carbonates water becomes soft.
Ca (HCO3)2 CaCO3 + CO2 + H2O
Mg (HCO3)2 MgCO3 + CO2 + H2O
, CAN ACADE
TT MY
Bhatti Street Near Mann–o–Salwa Tulsa Road Lalazar Rwp Ph: 051-8442595, WE OWN OUR STUDENTS
5122139, Cell: 0345-5930370
CLARK’S METHOD: Temporary hardness of water can be removed on the large scale by us-
ing Clark’s method. According to this method an estimated amount of slaked lime Ca (OH)2 is
added in hard water. The slaked lime reacts with hydrogen carbonated and form insoluble car-
bonates. These insoluble carbonates are allowed to settle down at the bottom and soft water is
collected from the top. Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O
Mg(HCO3)2 + Ca(OH)2 CaCO3 + MgCO3 + 2H2O
METHOD TO REMOVE PERMANENT HARDNESS:
Two methods are used to remove permanent hardness of water.
1) By adding washing soda 2) By ion exchange method
1) BY ADDING WASHING SODA: On the large scale permanent hardness of water can be
removed by adding washing soda (Na2CO3. 10H2O). As a result of this washing soda calcium
(Ca+2) and magnesium (Mg+2) ions are removed and produce insoluble carbonates. These insol-
uble carbonates settle down at the bottom and soft water is separated from top.
Ca+2 + C𝑂−2 CaCO3
3
Mg+2 + C𝑂−2
3
MgCO3
2) ION EXCHANGE METHOD:
On the large scale ion exchange method is used to remove permanent hardness of water. In this
method the hard water is passed through a container filled with a suitable resin containing
sodium ions. For this purpose a special sodium ion is used which is known as sodium zeolite.
Sodium zeolite is natural ion exchanger. It is written as Na2Z. This sodium zeolite exchange
Calcium (Ca+2) and magnesium (Mg+2) ions which cause hardness. Sodium zeolite is
chemically known as sodium aluminum silicate.
Ca+2 + Na2Z 2Na+ + CaZ
Mg+2 + Na2Z 2Na+ + MgZ
The ion exchange method is very economical method because the zeolite ions can be
regenerated by heating with concentrated solution of NaCl.
CaZ + 2NaCl Na2Z + CaCl2
DISADVANTAGE OF HARD WATER:
i) Hard water wastes large amount of soap when it is used for washing.
ii) The soap forms scum with hard water. This scum can spoil the finish of some fabrics.
iii) Hard water form insoluble calcium and magnesium salts. These salts can block car
radiators, boilers and hot water pipes.
iv) Hard water can cause kettles to fur.
