Permanganate titrations have been the easiest redox titration to get working. I've succeeded in standardizing with:
oxalic acid dihydrate (see above under alkalimetry)
potassium tetroxalate dihydrate (loc. cit.)(somewhat unsatisfactory)
potassium ferrocyanide trihydrate (prepared by reduction of photographic red prussiate of potash)
"tartar emetic", potassium antimonyl tartrate sesquihydrate (prepared from cream of tartar and pottery-store antimony trioxide)
I tried preparing "Mohr's salt" or ferrous ammonium sulphate hexahydrate from horticultural ferrous sulphate and ammonium sulphate and a dash of sulphuric acid, and got clean-looking crystals, but they seemed to be about 1% deficient in ferrous iron consistently. My guess is that Mohr's salt tends to contamination by other bivalent metals that substitute freely for Fe in the "Tutton salt" crystal structure and thus cannot be readily removed by recrystallisation.
