Manganese sulphide is reported as being green, pink, brown, white and also grey so we wanted to see if we could make some. We did 3 runs and each
ended up with different colors.
1) 30g MnSO4 was dissolved in 60ml water and 15g Na2S in 100ml water (the MnSO4 was from a garden center and the Na2S from a photography supplier so
unsure about purity). The solutions were mixed and stirred. There was initially a light brown suspension with some smell of H2S. Boiled the solution
for 5 minutes and it became dark brown. Filer and dried the dark brown precipitate on a watch glass on a boiling pot, eventually got 9.8g of bone dry
chocolate colored grains. The dark brown grains reacts vigorously with HCl with the generation of H2S.
We also boiled down the filtrate and got 3.4g of white powder. This powder shows no reaction with HCl, and when dissolved in water and mixed with a
solution of calcium nitrate there is no precipitate of calcium sulphate.
Q: The brown grains seems very stable with no smell of H2S but certainly contains sulphide. Is it MnS or a double sodium-manganese salt?
Q: If the white powder from the filtrate is not sodium sulphate, when then happened to the sulphate ions?
2) 15g Na2S in 100ml water and 15g MnCl2 in 50ml water. Mix and stir. Light fleshy pink solution formed. Upon boiling the color slowly changed to
light green. Light green precipitate was filtered off. As it dried, it started to become brown slowly. 7.5g of this green-brown powder was recovered.
It reacts with HCl to give H2S.
Q Is this green-brown powder likely to be mostly MnS?
3) 25g Ns2S in 80ml water and 15g MnCl2 in 80ml water. Mix. Pink solution. Stir for a few minutes without heating and filter. Pinkish filtrate.
Started to go grey as it dried. Transferred to a jar when still a moist paste to keep most of it the pinkish color. It also reacts with HCl to give
H2S, but not as vigorous as the brown grains (maybe because it is a bit wet still?). 15.8 g recovered.
Q Is this pinkish paste likely to be mostly MnS (excluding some water)?
We will have another go once we have some ammonia sulphide.
Boffis - 9-12-2019 at 14:30
OK Lion850 some possible answers bearing in mind that manganese 2+ sulphide is rather unstable in water.
1/Q1 The brown ppt is a manganese III/IV oxide of uncertain compositions produced by the hydrolysis of the manganese sulphide by water and air but
this reaction is obviously not complete hence H2S evolution on addition of acid.
1/Q2 The white product is sulphur from the oxidation of the displaced sulphide ions resulting from hydrolysis but the failure of the calcium nitrate
test is probably due to the fact that unless you filtered off the white ppt how would you see the new calcium sulphate ppt? What did you test with
with calcium nitrate? How long did you wait, in the presence of some ions it can take a hour or more before gypsum ppts?
2 Pure ppt MnS is pale pinkish in colour but the fine grained ppt is very susceptible to oxidation, natural MnO (pyrochroite) is emerald green and
transparent when fresh but darkens on exposure in minutes. The product of oxidation is an amorphous chocolate brown manganese oxide of variable
composition
3 prety much the same as above. Natural MnS, alabandite tends to be brown to black but that is due to the presence of iron.S.C. Wack - 9-12-2019 at 18:11
Manganese sulphide is reported as being green, pink, brown, white and also grey
And red. Are these results from following directions, or not?Lion850 - 10-12-2019 at 18:40
Hi S C Wack - not any directions: the directions I could find to make manganese sulphide by double displacement all calls for Ammonium Sulphide to be
used (and not Sodium or Potassium Sulphide). Just wanted to see what happened using what I had.
Hi Boffis:
/Q1 The brown ppt is a manganese III/IV oxide of uncertain compositions produced by the hydrolysis of the manganese sulphide by water and air but this
reaction is obviously not complete hence H2S evolution on addition of acid.
LEON: I expected the dried brown ppt to then still be breaking down the remainder of the iodide but it has no smell.
1/Q2 The white product is sulphur from the oxidation of the displaced sulphide ions resulting from hydrolysis but the failure of the calcium nitrate
test is probably due to the fact that unless you filtered off the white ppt how would you see the new calcium sulphate ppt? What did you test with
with calcium nitrate? How long did you wait, in the presence of some ions it can take a hour or more before gypsum ppts?
LEON: I left it for 12 hours but I must add I used very small quantities. Maybe too little. The white 'salt' left over after boiling dry the filtrate
of the first attempt is what I re-dissolved in some water to test with the calcium nitrate.
2 Pure ppt MnS is pale pinkish in colour but the fine grained ppt is very susceptible to oxidation, natural MnO (pyrochroite) is emerald green and
transparent when fresh but darkens on exposure in minutes. The product of oxidation is an amorphous chocolate brown manganese oxide of variable
composition
LEON: It will be interesting to see if the pale pink ppt remains pink if dried under argon or another atmosphere without oxygen and moisture.
3 prety much the same as above. Natural MnS, alabandite tends to be brown to black but that is due to the presence of iron.S.C. Wack - 11-12-2019 at 04:03
Vanino said he made reddish MnS by mixing equal mols. of hydrates of Na2S and various Mn salts. Apparently by grinding them together with mortar and
pestle, but he doesn't really say.
