Sciencemadness Discussion Board

phosphomolybdic acid synthesis

Karkov - 10-4-2019 at 07:28

When synthesizing PMA why does it sometimes change to green and sometimes yellow? I have done several experiments but can not find a correlation on why it’s doing that when each experiment is the same.

[Edited on Apr04-10-2019 by Karkov]

CharlieA - 10-4-2019 at 16:16

Molybdenum exhibits many oxidation states with, generally, characteristic colors. See for example Is the preparative procedure that you are following published? If so, does it suggest the colors of various possible products or by- products?

j_sum1 - 10-4-2019 at 20:50


Blue phosphomolybdates are famous -- often referred to as molybdenum blue, although this title serves a wide range of different species. Their structures are really interesting and have very high molecular mass and are extremely vivid in colour. Thus they serve as a means for titrating phosphate compounds.
My guess is that you have some of these included in your mixture -- probably as a result of something reducing the yellow compound.