Methylene blue and diphenylbenzidine sulfonic acid are redox indicators that turn from colorless in the reduced state to blue (methylene blue) or violet (diphenylbenzidine sulfonic acid) in the oxidized state. Indicate whether each is a suitable indicator for the following redox titrations.
(a) Reduction of Fe3 by Sn2 in 1M HCl: Methylene blue: suitable or unsuitable
(b) Reduction of Ce4 by Fe2 in 1M HCl: Methylene blue: suitable or unsuitable