Manganese

Chemical reactions




Reaction of manganese with acids


Manganese dissolves readily in dilute sulphuric acid, forming a colorless solution of Mn(II) ions and hydrogen gas, H2.

Mn(s) + H2SO4(aq) Mn2+(aq) + SO42−(aq) + H2(g)


Reaction of manganese with air


Manganese is not very reactive in regards to air. The surface of manganese lumps oxidizes a little. Finely divided manganese metal burns in air. In oxygen the oxide Mn3O4 is formed and in nitrogen the nitride Mn3N2 is formed.

3 Mn(s) + 2 O2(g) Mn3O4(s)
3 Mn(s) + N2(g) Mn3N2(s)


Reaction of manganese with ammonia


Manganese(II)-ions are precipitated by ammonia as manganese(II)hydroxide. The precipitation is incomplete

H2O(l) + NH3(aq) NH4+(aq) + OH(aq)
Mn2+(aq) + 2 OH(aq) Mn(OH)2(s) [white]


Reaction of manganese with halogens


Manganese reacts with the halogens, forming the corresponding manganese(II) halides. For fluoride, manganese(III)fluoride is also formed.

Mn(s) + F2(g) MnF2(s)
2 Mn(s) + 3 F2(g) 2 MnF3(s)
Mn(s) + Cl2(g) MnCl2(s) [3]
Mn(s) + Br2(g) MnBr2(s)
Mn(s) + I2(g) MnI2(s)


Mn(II)-ions are readily oxidized to MnO2 by bromine under alkaline conditions

Mn2+(aq) + Br2(aq) + 2 OH(aq) MnO2(s) [brown-black] + 2 HBr(aq)

Manganese with oxidation steps >2 will be reduced to Mn(II) by Br and I under acidic conditions under the formation of Br2 and I2 respectively, e.g.

MnO2(s) + 2 Br(aq) + 4 H+(aq) Mn2+(aq) + Br2(aq) + 2 H2O(l)
MnO2(s) + 2 I(aq) + 4 H+(aq) Mn2+(aq) + I2(aq) + 2 H2O(l)


Reaction of manganese with hydroxide ions


Manganese(II)-ions are precipitated by hydroxide ions forming white precipitate

Mn2+(aq) + 2 OH(aq) Mn(OH)2(s) [white]


Reaction of manganese with metals/metal ions


Manganese with oxidation steps >2 will be reduced to Mn(II) by Sn(II) under acidic conditions under the formation of Sn(IV), e.g.

MnO2(s) + Sn2+(aq) + 4 H+(aq) Mn2+(aq) + Sn4+(aq) + 2 H2O(l)

Manganese compounds with oxidations step <7 is oxidized in nitric acid by lead oxide red to permanganate e.g.

2 Mn2+(aq) + 5 Pb3O4(s) + 24 H+(aq) MnO4(aq) + 15 Pb2+(aq) + 12 H2O(l)


Reaction of manganese with peroxide


Mn(II)-ions are readily oxidized to MnO2 by hydrogen peroxide under alkaline conditions

Mn2+(aq) + H2O2(aq) + 2 OH(aq) MnO2(s) [brown-black] + 2 H2O(l)

The general rule for manganese compounds reacting with a surplus of hydrogen peroxide under acidic conditions is the oxidation to Mn(II). Under alkaline conditions in a surplus of hydrogen peroxide, MnO2 is formed.

2 MnO4(aq) + 5 H2O2(aq) + 6 H+(aq) 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g)
MnO2(s) + H2O2(aq) + 2 H+(aq) Mn2+(aq) + 2 H2O(l) + O2(g)


Reaction of manganese with phosphates


Manganese(II) ions are not precipitated by phosphate ions in acetic acid. In the presence of ammonium ions, a rosa precipitate is formed:

Mn2+(aq) + NH4+(aq) + PO43−(aq) MnNH4PO4(s)


Reaction of manganese with sulfide


Manganese(II)-ions are not precipitated by sulfide using H2S and HCl. Na2S under neutral to slightly alkaline conditions will precipitate Mn(II) forming the pink MnS. The precipitate is readily dissolved in acid, even weak acids like acetic acid:

Mn2+(aq) + H2S(aq)
Mn2+(aq) + Na2S(aq) MnS(s) [pink] + 2 Na+(aq)
MnS(s) + 2 H+(aq) Mn2+(aq) + H2S(aq)

Manganese with oxidation steps >2 will be reduced to Mn(II) under acidic conditions under the formation of S(s), e.g.

MnO2(s) + H2S(aq) + 2 H+(aq) Mn2+(aq) + 2 H2O(l) + S(s)


Reaction of manganese with sulfoxide


Manganese with oxidation steps >2 will be reduced to Mn(II) under acidic conditions under the formation of SO42−(aq), e.g.

MnO2(s) + SO2(g) Mn2+(aq) + SO42−(aq)


Reaction of manganese with water


Manganese reacts slowly with water [2,3]:

Mn(s) + 2 H2O(l) MnO2(s) + 4 H+(aq) + 4 e E° = -0.024 V
Mn2+(aq) + 4 H2O(l) MnO42−(aq) + 8 H+(aq) + 4 e E° = -1.742 V
Mn2+(aq) + 4 H2O(l) MnO4(aq) + 8 H+(aq) + 5 e E° = -1.507 V
3 MnO42−(aq) [green] + 2 H2O(l) 2 MnO4(aq) [purple] + 4 OH(aq) + MnO2(s)


Quantitative analysis


Method 3500-Mn C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.01 mg/L
Method limit of detection in soil = 10.0 mg/kg