Titration of cerium (IV) sulphate with sodium oxalate at the room temperature using ferroin as internal indicator

Summary A method has been developed for the titration of cerium(IV) sulphate with sodium oxalate at the room temperature, using ferroin as internal indicator. A new principle has been utilised for facilitating the indicator action at the equivalence point. This involves the use of a photochemical reaction between the oxalate and iron(III) which is deliberately added to the mixture containing cerium(IV) sulphate and ferriin. When the mixture is titrated with the sodium oxalate solution under exposure to the light from a Philips Repro lamp, the addition of a very slight excess of sodium oxalate solution, after all the cerium(IV) sulphate has reacted, produces a vivid red colour. The slight excess of sodium oxalate added reacts with the iron(III) salt photochemically producing a trace of iron(II) salt which reduces the ferriin to the red ferroin. In titrations with 0.1 and 0.05 N solutions of sodium oxalate, the error is negligible. In titrations with sodium oxalate solution of lower strengths, the error amounts to 0.02 ml of 0.01 N oxalate which has to be subtracted from the titre.