Determination of Total, Permanent and Temporary Hardness of Water

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Aim

To determine the Total, Permanent and temporary hardness of given water sample.

Apparatus

Burette, pipette, conical flask.

Reagents

  1. 01M EDTA (Ethylene Di-amine Tetra Acetic Acid)
  2. Ammonia buffer solution
  3. Eriochrome black-T

Theory

Hardness in water is defined as that property which prevents lathering of soaps. It is caused clue to the presence of dissolved materials such as carbonates, bi-carbonates, chlorides, nitrates and sulphates of calcium and magnesium.

Types of Hardness

  1. Temporary hardness or Carbonate hardness
  2. Permanent hardness or Non-carbonate

Temporary hardness in water is caused due to the presence of bicarbonates of calcium and magnesium and boiling or addition of lime can easily remove this.

Permanent hardness is caused due to the presence of sulphates, chlorides and nitrates of calcium and magnesium. This cannot be removed by boiling but requires special treatment such as demineralization, ion exchange etc.

Hardness is expressed as mg/It on calcium carbonate scale. The desirable (permissible) limit of total hardness in potable waters is 300mg/l and maximum permissible limit is 600 mg/l.

Principle

EDTA Titrimetric Method

A compound called Ethylene Di amine Tetra Acetic acid is made use of in this method.  In alkaline condition the Ca2+ and Mg2+ develops a wine red colour with eriochrome black-T indicator. When EDTA is added as a titrant, the Calcium and Magnesium ions get complexed resulting in a sharp change from wine red to blue, which indicates the end point of the reaction.

Procedure

Total Hardness

  1. Pipette out 25m1 of the given water sample into a conical flask.
  2. Add 1m1 of ammonia buffer solution and 3 drops of Eriochrome black-T indicator to it. The solution turns wine red in color.
  3. Titrate this solution against 0.01 M EDTA taken in a burette till the color changes from wine red to blue which indicates the end point.
  4. Note down this burette reading.

Observation

Trial No Initial Reading Final reading Difference
1      
2      
3      
4      

Permanent Hardness or Non Carbonate Hardness

  1. Take about 50 ml of the given water sample, boil and cool it to remove temporary hardness.
  2. Transfer 25 ml of this solution into a clean conical flask.
  3. Add l ml of ammonia buffer solution and 3 drops of Eriochrome black-T indicator to it. The solution turns wine red in colour.
  4. Titrate this solution against 0.01 M EDTA taken in a burette till the colour changes from wine red to blue which indicates the end point.
  5. Note down this burette reading which gives the volume of EDTA consumed.

Observation

Trial No Initial Reading Final reading Difference
1      
2      
3      
4      

 Calculation

Total hardness = [A × B × 1000] / ml of sample =                    mg/l as CaCO3 Where,

A = Volume of EDTA consumed.

B = 1 (mg of CaCO3 equivalent to 1m1 of EDTA titrant)

Permanent hardness = [C × D × 1000] / ml of sample =                    mg/l as CaCO3 Where,

C = Volume of EDTA consumed for titrating the boiled and cooled sample.

D = 1 (mg of CaCO3 equivalent to 1m1 of EDTA titrant)

Temporary hardness = Total hardness – Permanent hardness

=…………-……….=…………….. mg/l as CaCO3

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