Notes on Hardness of Water | Grade 9 > Science > Water | KULLABS.COM

## Hardness of Water

• Note
• Things to remember
• Videos
• Exercise
• Quiz

#### Hard and soft Water

Water is a universal solvent. It can dissolve many substances. Some dissolved substances may be useful where some may not be. Mostly, the salts of various metals (mostly magnesium and calcium) like magnesium sulphate, calcium sulphate, magnesium chloride, magnesium bicarbonate, calcium chloride etc. are mixed in water which makes the hardness in water. There are two types of water, soft water and hard water. Hard water is a type of water which cannot form lather with soap and soft water is a type of water which can form lather with soap.
The hardness of water is of two types, permanent hardness and temporary hardness. Permanent hardness is due to chloride and sulphate salt of calcium and magnesium. In this type, the hardness of water cannot be removed easily. In a temporary type of hardness, the hardness of water can be removed by boiling the water. Temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate.

##### Removal of Temporary Hardness

There are various methods for the removal of temporary hardness of water. Some mostly used methods are discussed below,

1. By heating: As we know that, the temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate. When we heat, calcium bicarbonate and magnesium bicarbonate change into insoluble salts.
Ca(HCO3)2 $$\overset{Heat}{\rightarrow}$$ CaCO3↓ + H2O + CO2

Mg(HCO3)2$$\overset{Heat}{\rightarrow}$$ MgCO3 + H2O + CO2

2. Treating with lime water: Another way of removal of temporary hardness of water is by treating water with lime water. The chemical equation is given below,
Ca(HCO3)2 + Ca(OH)2→ 2CaCO3↓ + 2H2O

Mg(HCO3)2+Ca(OH)2→ MgCO3 + CaCO3↓ + 2H2O
##### Removal of Permanent Hardness

Permanent hardness of water is due to the presence of salts such as magnesium chloride, magnesium sulphate, calcium chloride, etc. We can remove the permanent hardness of water by following methods which are highlighted below,

1. By treating with washing soda: Permanent hardness of water can be removed by treating it with washing soda. As we know that, the permanent hardness of water is due to soluble salts of calcium and magnesium so when we treat them with washing soda, it changes into insoluble salts.
CaCl2 + Na2CO3→ CaCO3↓ + 2NaCl
CaSO4 +Na2CO3→CaCO3↓ + Na2SO4
MgCl2 +Na2CO3→ MgCO3↓ + 2NaCl
MgSO4 + Na2CO3→ MgCO3↓ +Na2SO4

2. Permutit Process: One of the methods for removal of permanent hardness is Permutit process. In permutit process, sodium zeolite or sodium aluminium orthosilicate used which is prepared by fusing sodium carbonate silica and alumina. Its composition resembles Na2Al2SiO8 or Na2Z, where, Z stands for zeolite= Al2SiO8.
At first in permutit process, the cylinder is packed with permutit. Then the hard water is passed through the cylinder. Here, the all the ions of soluble salts of calcium and magnesium are replaced by sodium ions. Since the amount of sodium ions decreases as it reacts with the ions of soluble salts of calcium and magnesium, this can be regenerated by soaking in a 10%solution of common salt when the reverse change takes place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.

Ca++ + Na2Z→ CaZ↓ + 2Na+
Sodium zeolite
Mg++ + Na2Z→ MgZ↓ + 2Na+
Sodium zeolite
[Note: Z = Al2Si2O8.(H2O)]

• Used in beer industries.
• Water becomes tasty to dissolved salts of calcium and magnesium.
• It helps in the development of bones and teeth as it contains calcium salt.

• A large amount of soap is wasted.
• Unfit for drinking
• Unfit for use in the steam boiler.

• Hard water is a type of water which cannot form lather with soap and soft water is a type of water which can form lather with soap.
• Permanent hardness of water can be removed by treating it with washing soda.
•  One of the methods for removal of permanent hardness is Permutit process.
• Permanent hardness of water is due to the presence of salts such as magnesium chloride, magnesium sulphate, calcium chloride, etc.
• Temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate.
.

### Very Short Questions

Any three advantages of hardwater are as follow,

• It is used in beer industries.
• Water becomes tasty to dissolved salts of calcium and magnesium.
• It helps in the development of bones and teeth as it contains calcium salt.

The temporary hardness of water can be removed by heating the water and by treating it with lime water. Here, we discuss how hardness of water can be removed by heating.

As we know that, the temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate. When we heat, calcium bicarbonate and magnesium bicarbonate change into insoluble salts.
Ca(HCO3)2 $$\overset{Heat}{\rightarrow}$$ CaCO3↓ + H2O + CO2

Mg(HCO3)2$$\overset{Heat}{\rightarrow}$$ MgCO3 + H2O + CO2

Permanent hardness of water can be removed by treating it with washing soda. As we know that, the permanent hardness of water is due to soluble salts of calcium and magnesium so when we treat them with washing soda, it changes into insoluble salts.
CaCl2 + Na2CO3→ CaCO3↓ + 2NaCl
CaSO4 +Na2CO3→CaCO3↓ + Na2SO4
MgCl2 +Na2CO3→ MgCO3↓ + 2NaCl
MgSO4 + Na2CO3→ MgCO3↓ +Na2SO4

0%

2 types
5 types
3 types
4 types

Simple water
Clean water
Hard water
Soft water

Tough water
Tight water
Hard water
Soft water
• ### Which one of the following is not the method of removal of permanent hardness of water?

Permutit process
By heating
By treating with washing soda
• ### In which method of removal of permanent hardness of water, is sodium zeolite or sodium aluminium orthosilicate used?

Bessemer's process
Permutit process
Hard removal process
Dalton's process
• ### Temporary hardness of water is due to

Calcium bicarbonate and magnesium bicarbonate.
Calcium phosphate and magnesium phosphate
Calcium chloride and magnesium chloride
Calcium silicate and magnesium bicarbonate
• ### Permanent hardness is caused due to

Magnesium sulphate
Magnesium carbonate
All of the above
Magnesium bicarbonate

Typhoid
Cholera
Scabies
Hepatitis
• ### If pH value of water is

7 water is said to be neutral
Less than 7 it is said to be acidic
More than 7 it is said to be alkaline
all
• ### Which one of the following is not the advantgae of hard water?

It helps in the development of bones and teeth as it contains calcium salt.
Unfit for drinking
Used in beer industries.
Water becomes tasty to dissolved salts of calcium and magnesium.
• ## You scored /10

Forum Time Replies Report

##### Rakesh

Property of permutit??

##### Amrit

What is the principle of softening of hard water? Explain it.