Manganese

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)

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)

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]

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)

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

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

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)

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)

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)

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)

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)

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)

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