Determination of Alkalinity of Water

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Aim

To determine the alkalinity of water.

Apparatus

Burette, pipette, conical flask, measuring jar, volumetric flasks (1000ml, 200ml, 100ml)

Reagents

  1. 0.02N H2SO4
  2. Methyl orange indicator
  3. Phenolphthalein indicator
  4. Sodium thio sulphate 0.1 N

Theory

Alkalinity of a sample is a measure of its capacity to neutralize acids. It is mainly due to the salts of weak acids and some times due to weak or strong bases, mainly due to hydroxides, carbonates and bicarbonates. Highly alkaline water leads to embitterment and causes deposition of precipitates in boiler tubes. Bicarbonates of calcium and magnesium induce temporary hardness to water. Other forms of alkalinity include Hydroxide alkalinity, Carbonate alkalinity and Bicarbonate alkalinity. Generally high alkalinity waters are un-potable and may physiologically affect the consumers. It is a very important parameter in corrosion control.

Procedure

Phenolphthalein Alkalinity

  1. Take 25ml of sample (Water) in .a conical flask, add 2-3 drops of phenolphthalein indicator.
  2. Titrate the contents in the conical flask with 0.02N H2SO4. The  end  point is pink to colorless.
  3. Note the burette reading, which gives the volume of H2SO4 Consumed. Repeat till two concurrent values are obtained.

Observations

Trial No Initial Reading Final reading Difference
1      
2      
3      
4      

Calculation

P = [A × N × 50 × 1000] / ml of sample =                    mg/l as CaCO3

Where,

A = Volume of H2SO4 consumed. N = Normality of H2SO4 (0.02)

Result:

Procedure 

Total Alkalinity

  1. Take 25m1 of sample (Water) in a conical flask, add 2-3 drops of Methyl-orange indicator.
  2. Titrate the contents in the conical flask with 0.02N H2SO4. The end point is pale yellow to pale pink.
  3. Note the burette reading, which gives the volume of H2SO4.
  4. Repeat until two concurrent values are obtained.

 

Observations

Trial No Initial Reading Final reading Difference
1      
2      
3      
4      

Calculation

T = [B ×N × 50 × 1000] / ml of sample=                    mg/l as CaCO3 Where,

B = Volume of H2SO4 consumed.

N = Normality of H2SO4 (0.02)

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