[hebism]

Hi,
I tried to prepare Mn(NO3)2 in the lab using Mn powder and dil HNO3, filter and dry. I got brown powder and I tested the nitrate ion in the product solution using NaOH and Al-foil but I got Red brownish fumes and it should be ammonia fumes.
Does any know correct method to prepare Mn(NO3)2?
Thanks

[sjb]

Hi,
I tried to prepare Mn(NO₃)₂ in the lab using Mn powder and dil HNO₃, filter and dry. I got brown powder and I tested the nitrate ion in the product solution using NaOH and Al-foil but I got Red brownish fumes and it should be ammonia fumes.
Does any know correct method to prepare Mn(NO₃)₂?
Thanks

Uhlmann's suggests MnCO₃ + HNO₃ - see https://en.wikipedia.org/w/index.php?title=Manganese(II)_nitrate&oldid=703933419 which may also explain your fumes.

[hebism]

Mn+HNO3=Mn(NO3)2+H2 (gas)
MnCO3+HNO3=Mn(NO3)2+H2O+CO2(colorless gas)

[Borek]

Nitric acid is a strong oxidizer, it will do more than you need when given metal to react with. MnCO₃ and (reasonably) diluted acid sounds like a better option (even if Mn²⁺ can probably reduce NO₃^-).

[Hunter2]

Most metalls depending onn the concentration of the HNO₃ will be dissolved under NO_x development.

Me + 4 HNO₃ => Me(NO₃)₂ + 2 NO₂ + 2 H₂O

So the recomandation to use Carbonate or maybe also the Hydroxide will be more safe.

Other option would be to use AgNO₃ and MnCl₂

It will give a precipitation of AgCl and Mn(NO₃)₂ will be left.

[hebism]

well, I prepared MnCO3 from MnCl2 and Na2CO3(reaction for 24h) after that I mix MnCO3 with Dil HNO3 (10%)(reaction for 20min) then filter, and evaporate the filtrate but after evaporation I didn't get any product(flask was empty).

[hebism]

what is the reaction time for AgNO3 and MnCl2?

[Hunter2]

Seconds

[Hunter2]

well, I prepared MnCO3 from MnCl2 and Na2CO3(reaction for 24h) after that I mix MnCO3 with Dil HNO3 (10%)(reaction for 20min) then filter, and evaporate the filtrate but after evaporation I didn't get any product(flask was empty).

My question is why you have to filter after add nitric to the manganese carbonate. I think your manganese was oxidized to MnO₂ . After filtering you have only water and nitric in the flask.

[hebism]

I filtered to getrid of unreacted MnCO3, I found dark brown residue in filter paper can't be removed

[Burner]

I mix MnCO3 with Dil HNO3 (10%)(reaction for 20min) then filter

If I have not mistaken in my calculations, 10% HNO₃ is about 2.4M, which maybe still too concentrated to prevent unwanted oxidation. I learnt from school that if only acid-base reactions are desired, 'very dilute'(<0.1M) HNO₃ is used.

I found dark brown residue in filter paper can't be removed

Likely to be MnO₂

[Hunter2]

Other cheaper option would be to start wie MnSO₄ and Ba(NO₃)₂ you get BaSO₄ as precipitate and Mn(NO₃)₂ will be in the solution. Cheaper as to use AgNO₃.