Chloride

ESTIMATION OF CHLORIDE

Principle

         Chloride ions in irrigation water can be determined by titration with standard silver nitrate solution using potassium chromate as an indicator. By addition of AgNO3 all the chloride is precipitated as silver chloride and any further addition of AgNO3 produces a flesh red colour precipitate of silver chromate, which is the end point of the titration.

         NaCl + AgNO3                     →             AgCl ↓ + NaNO3

         K2CrO4 + 2AgNO3   →             Ag2CrO4 ↓   + 2KNO3

Reagents required

1.      Silver Nitrate Solution (0.1 N)

2.      Potassium Chromate Solution

Procedure

         Pipette out 25 or 50 ml of water sample into a porcelain basin. Add few drops of K2CrO4 indicator solution. Titrate against 0.1 N AgNO3 with constant stirring by means of a glass rod until the addition of a drop produces flesh red coloration throughout the mixture in the basin.

Calculation

Volume of 0.1 N AgNO3 consumed              = V ml

1 ml of N/10 AgNO3                                                                   = 0.00355 g of chloride

50 ml of water sample contains                      = 0.00355 x V g of chloride

Therefore 1000 liters (ppm)                            = 0.00355 x V x 1000 x 1000/50

In terms of milli equivalents per liter               = ppm/35.5