Electroanalysis of silver and mercury by the use of EDTA

Studies on electroanalysis by the use of EDTA. IVV

Abstract

Conditions for the electrolytic determination of silver and mercury, and the method of electrolytic separation of each metal from copper have been studied in the case of the procedure employing EDTA.
As for silver, the following conditions are suitable for its determination: the pH of the solution, containing twice as much EDTA in molar ratio as silver, is adjusted to 910 with aqueous sodium hydroxide, and the solution is electrolyzed at a bath voltage of 1.22V and at a temperature of 50°C or thereabout. Silver, less than 108mg, can be quantitatively determined as a very lustrous deposit, but if its amout is 160mg or more, accurate results are not obtained. By this method, its quantitative separation can be made in the presence of more than 600 mg of copper.
As for mercury, it was proved that a very beautiful deposit can be obtained even in the absence of depolarizer. The platinum cathode must be plated with silver before use. If the pH of the solution, containing 34 times as much EDTA in molar ratio as mercury, is adjusted to 35 with sodium carbonate solution, and the solution is electrolyzed at a bath voltage of 23 V at room temperature, 60120 mg mercury can be quantitatively determined as a lustrous deposit. After electrolysis, the cathode is washed with water, acetone, and ether in sequence, then dried with an electric fan. Coexisting copper, less than 150mg, does no harm, but if its amount is over 190mg, a positive error results.