Estimation of ferric salts through photochemical reduction with oxalic and lactic acids

Abstract

1. The photochemical reduction of ferric sulphate in sunlight by oxalic and lactic acids has been studied with a view to its analytical application. Conditions have been developed under which ferric sulphate is reduced quantitatively to the ferrous state, so that it can be estimated accurately by titration with a standard solution of sodium vanadate. 2. The rate of photoreduction of ferric salt with oxalic acid is not very much influenced by variation of the concentration of sulphuric acid in the medium from 0.4 N to 1.6 N. Whereas, the speed of the photochemical reaction of ferric salts with lactic acid is greatly retarded by an increase in the sulphuric acid concentration. The results indicate that the photochemical reaction in either case is due to the formation of ferric complexes with the organic acid. The photochemically active ferri-oxalate complex or complexes appear to be stable in acid medium while the corresponding lactic acid complex appears to be stable in neutral or weak acid solution and to undergo appreciable dissociation with increasing acidity.