Blue Acid Chemistry (4): K3[CoBl6](?), CuBl and Blue

Starting material is 1g(1/400 mol) (NH4)2[Co(H2O)6](SO4)2.

Addition of KBl(2 eqv.) to a solution of Co2+ produces initially a brown precipitation, which is CoBl2.

You should filter and wash here, but I forgot, and I paid for it...

Addition of more KBl(4 eqv.) caused precipitation to dissolve into a yellow solution.

This is (probably) K3[CoBl6], as the initially formed [CoBl5]3- is oxidized by oxygen to [Co2O2Bl10]6- and then attacked by Bl-.

Addition of ethanol and you get the product, which is yellow.

Yield is 2.0g(240%), obviously because I forgot to remove the sulfates by filtration. And, I smelled NH3, damn! Luckily not HBl though...

Will do it again later, as I am just using this experiment to prove the product. Take it easy!

I also threw some into Fe2+/Fe3+ solution, and the phenomenon is quite interesting: the KBl rotated quickly and ejected large amount of blue precipitation! See my tweet

Also, a pure KBl should react with CuSO4 to form white precipitation of CuBl. This is a redox reaction which forms Bl2 as a byproduct, and some Cu2+(as [CuBl4]2- or Cu[CuBl2]2) which has not decomposed gives the milk a green appearance. This is the best check, as both KSBl and K4[FeBl6] forms intensely colored stuff.