Determination of Chlorides in Water

Aim

To determine the chlorides in water by Mohr’s method.

Apparatus

Burette, pipette, conical flask, measuring jar.

Reagents

  • 0141 N Silver nitrate (AgNO3)
  • Potassium chromate (K2Cr04) indicator

Theory

If water containing chlorides is titrated with silver nitrate solution, chlorides are precipitated as white silver chloride. Potassium chromate is used as indicator, which supplies chromate ions. As the concentration of chloride ions approaches extinction, silver ion concentration increases to a level at which reddish brown precipitate of silver chromate is formed indicating the end point.

Procedure

  1. Pipette out 50m1 of the given water sample into a clean conical flask
  2. Add 3 drops of Potassium chromate indicator. The solution turns yellow in color
  3. Titrate this with 0.0141 N AgNO3 to a stable reddish brown or brick red precipitate.

Observations

Trial NoInitial ReadingFinal readingDifference
1
2
3
4

 

Calculation

Chlorides = [(A-B) x  N  x  35.460 x  1000] /  ml of sample =             mg/l.

Where,

A = Volume of Silver nitrate consumed. B = Blank Correction

N = Normality of AgNO3 (0.0141)

Total
0
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