Phthalocyanines as oxidation-reduction indicators

Summary

Investigations on the use of copper phthalocyanine tetrasulphonic acid (Cu-PTS) as a redox indicator in vanadametry have given the following results:

• 1. Cu-PTS serves well as a redox indicator in the titration of iron(II) with 0.05 N sodium vanadate solution while keeping the sulphuric acid concentration of the medium at 12 N and adding 3 ml of syrupy phosphoric acid for each 60 ml of the reaction mixture. The indicator correction is negligible. The addition of phosphoric acid can be avoided by carrying out the titration in 14 N sulphuric acid.

• 2. In the estimation of small quantities of iron(II) with 0.01 N sodium vanadate, it is possible to carry out the titration in 12 N sulphuric acid even without the addition of phosphoric acid. The indicator correction has been found to be 0.02 ml of 0.01 N vanadate, which is smaller than that required with diphenylbenzidine and N-phenylanthranilic acid.

• 3. Cu-PTS cannot be used as an inside indicator in the titration of iron(II) in hydrochloric acid medium.

• 4. Cu-PTS can be used as an internal indicator in the titration of uranium(IV) and molybdenum(V) with sodium vanadate, while keeping the sulphuric acid concentration of the mixture at 12 N and adding 3 ml of syrupy phosphoric acid.