Back-titration of silver (I) with sodium diethyldithiocarbamate

Abstract

The determination of silver in silver alloys was performed. The procedure is as follows : A sample was dissolved in nitric acid and the solution was diluted to 500 cm³ with water; an aliquot, containing (220)mg of silver, of the solution was transferred. into a conical beaker; 2 cm³of saturated sodium chloride solution was added; silver chloride formed was filtered off through a Toyo No. 5C filter paper. Copper, zinc and cadmium in the filtrate were determined by the titration with 0.01 mol dm^-3EDTA solution. The precipitate remaining on the filter paper was dissolved in aqueous ammonia. The solution was diluted to about 100cm³ with water; pH was adjusted to 10 with sulfuric acid; 15 cm³ of 0.02 mol dm^-3 diethyldithiocarbamate (NaDDTC)solution was added. After adding one drop of Bromothymol Blue indicator solution, the excess of NaDDTC was titrated with 0.01mol dm^-3 standard cadmium sulfate solution till the color turns from blue to red. This method was applicable to the determination of (860)% silver in silver coin or silver brazing filler metals.