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

Hardness of Water

Notes, Exercises, Videos, Tests and Things to Remember on Hardness of Water

Please scroll down to get to the study materials.

Registration open for Special Scholarships

  • 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)]




Advantages and Disadvantages of Hard Water

  • 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.

Disadvantage

  • 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.
.

Questions and Answers

Click on the questions below to reveal the answers

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%
  • How many types of water are there?

    3 types
    4 types
    2 types
    5 types
  • Which type of water cannot form lather with soap?

    Soft water
    Simple water
    Hard water
    Clean water
  • Which type of water can form lather with soap?

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

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

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

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

    Magnesium carbonate
    Magnesium bicarbonate
    Magnesium sulphate
    All of the above
  • Which of the following is not a water borne disease?

    Cholera
    Hepatitis
    Typhoid
    Scabies
  • If pH value of water is

    all
    Less than 7 it is said to be acidic
    7 water is said to be neutral
    More than 7 it is said to be alkaline
  • 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.
    Used in beer industries.
    Water becomes tasty to dissolved salts of calcium and magnesium.
    Unfit for drinking
  • You scored /10


    Take test again

ASK ANY QUESTION ON Hardness of Water


You must login to reply

Forum Time Replies Report


You must login to reply

Rakesh

Property of permutit??


You must login to reply

Amrit

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


You must login to reply

What is hardness of water?

What is hardness of water?


You must login to reply