Question

The arsenic (III) found in an insecticide residue was dissolved and titrated coulometrically by the
generation of bromine. At a constant current of 50 mA, it required 3.5 minutes for oxidation to
arsenic (V). Calculate the milligrams of As2O3 in the residue.

Answer 1

I= 50mA = 50*0.001= 0.05A

TIME = 3.5 min = 3.5*60 = 210 seconds

q= I*t = 0.05*210 =10.5 columbs

according to the reaction

3*96500 colubs deposit -------------------------------------------- 74.92 grams

10.5 columbs deposit -------------------------------------------------?

                        = 10.5*74.92/(3*96500)

                     = 0.0027 GRMAS