Volumetric determination with silver nitrate and potassium chromate visual indication

3 Volumetric determination with silver nitrate and potassium chromate (visual indication) 

If all chloride ions are bonded as AgCl, silver ions added in excess, together with chromate ions, form reddish-brown silver chromate (Ag2CrO ). 

The method is suitable for the determination of chloride ions in concentrations between 10 and 1 0 mg/1. Waters whose chloride-ion concentrations lie outside this range can also be determined according to this method by appropriate dilution or concentration. Its applicability to waste water investigation is dependent on the type of waste water involved. 

Coloured or turbid waters should be shaken out with chloride-free, freshly precipitated aluminium hydroxide or chloride free washed activated charcoal, and filtered. Organic substances are destroyed in a weakly alkaline solution with KMnOz, heating gently. Excess KlVlnO is eliminated with H2O2, the hydrated manganese oxides are filtered off and washed, chloride-free. 

Interfering S032 can be eliminated by H2O2 in neutral solution, and 5203 , CN and SCN can be eliminated by H2O2 in alkaline solution. Iron ions can be precipitated by shaking with 1 g of chloride-free zinc oxide and can then be filtered off. Phosphate interferes in concentrations greater than 25 mg/1. It is coprecipitated with iron. 

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