Oxidimetric methods for the volumetric determination of molybdenum(V)

Abstract

1 Detailed investigations have now been made on the titration of molybdenum(V) with ceric sulphate, using ferroin and diphenyl benzidine as internal indicators. The titration of molybdenum(V) with ceric sulphate using ferroin as indicator is best carried out in 3 N hydrochloric acid medium, with the addition of 5 ml of syrupy phosphoric acid for 50 ml of the reaction mixture. The titration of molybdenum (V) with ceric sulphate using diphenyl benzidine is to be carried out in a medium which is at least 4 N in hydrochloric acid, with the addition of 5 ml of syrupy phosphoric acid for 50 ml of the titration mixture. 2 Detailed investigations have also been carried out on the use of N-phenylanthranilic acid and diphenyl benzidine as internal indicators in the titration of molybdenum(V) with sodium vanadate. N-phenylanthranilic acid works as a satisfactory indicator in the titration of molybdenum(V) with sodium vanadate in a medium which is at least 6 N in acid concentration at the end point of titration. The titration can, however, be made with ease in 4 N acid medium if some oxalic acid is added (about 2 ml of 1.0 Molar oxalic acid for 50 ml of the mixture). For the titration of molybdenum(V) with sodium vanadate, using diphenyl benzidine as indicator, the acid concentration must be 4 N in hydrochloric acid, and some oxalic acid (about 2ml of 1.0 Molar solution for 50 ml of the mixture or some phosphoric acid (about 6 ml of syrupy phosphoric acid for 50 ml of the mixture) must be added. The titration can also be carried in 3 N hydrochloric acid medium, if both oxalic and phosphoric acids are added. 3 A detailed study of the mechanisms of the actions of the redox indicators in these titrations have revealed interesting induced and catalysed reactions.