Manganese

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Other names/abbreviations:

Mn

Element no:	25
Element group:	7 (IUPAC) VII B (American labelling) VII A (European labelling)
Element type:	Transition metals
CAS-Number:	7439-96-5
EINECS-Number:	231-105-1

Chemical properties

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
Mn(II)-ions are readily oxidized to MnO₂ by brome 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) + PO₄^3- (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 SO₄^2- (aq), e.g.

MnO₂ (s) + SO₂ (g) Mn²⁺ (aq) + SO₄^2- (aq)


Reaction of manganese with water
Manganese reacts slowly with water [2,3]:

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


Solubility
Water: Insoluble (20 °C) [5]
Diluted acids: Soluble (20 °C) [5]

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

Safety

Symbol: Xn
R-phrases: 48/20
S-phrases: 24/25

Physical properties

Appearance
	Physical state @ 20°C:	Solid [3]
	Color:	Grey-white with a slightly red tinge [3]
	Odor:	Odourless [5]

Bulk properties
	Molecular weight (g/mol):	54.93805(1) [2]
	Melting point (°C):	1244 [2]
	Boiling point (°C):	2060 [2]
	Density (g/cm3):	7.44 (20 °C) [4]
	Elastic properties: Young's modulus (GPa): Rigidity modulus (GPa): Bulk modulus (GPa): Poisson ratio:	191-202 [4] 79.5 [4] 92.6 [4] 0.25 [4]

Thermodynamic properties
	ΔfH°gas (kJ/mol):	281±6 (Monoatomic) [2] 280.7 [6]
	ΔfH°solid (kJ/mol):	0.0 [6]
	ΔH°fusion (kJ/mol):	12.91 [6]
	ΔH°vaporization (kJ/mol):	221±8 [2]
	S°gas (J/K·mol):	173.7 [6]
	S°solid (J/K·mol):	32.0 [6]
	ΔfG°gas (kJ/mol):	238.5 [6]
	Cp (gas) (J/K·mol):	20.8 (25 °C) [6]
	Cp (solid) (J/K·mol):	26.32 (25 °C) [6]
	Coeff. of linear thermal expansion (106 K-1):	21.7 (25 °C) [6]

Crystal structure
	Crystal type:	Cubic comp. [4]

Electronic properties
	Electron configuration:	1s2-2s2-2p6-3s2-3p6-3d5-4s2
	Ionic radius (Å):	Mn(VII): 0.46 (6-coordinate) [2] Mn(VI): 0.255 (4-coordinate) [2] Mn(V): 0.33 (4-coordinate) [2] Mn(IV): 0.53 (6-coordinate) [2] Mn(III): 0.58 (6-coordinate, low-spin) [2] Mn(III): 0.645 (6-coordinate, high-spin) [2] Mn(II): 0.67 (6-coordinate) [2]

Conductivity
	e°(V):	Mn(III)/Mn: -0.283 [1] Mn(II)/Mn: -1.185 [1]
	Electrical resisitvity (μΩ·cm):	160.00 (20 °C) [4] 144.00 (25 °C) [4]
	Thermal (W/m·K):	7.82 (27 °C) [6]

References

1: Standard Methods for the Analysis of Water and Wastewater, APHA, 1992, 18th edition

2: Greenwood,N.N., Earnshaw,A. Chemistry of the elements
2nd edition (1997) Edited by Greenwood,N.N., Earnshaw,A. pp. 1-1340, Butterworth-Heinemann. Oxford. Great Britain

3: General chemistry
7th edition (1984) Edited by Holtzclaw, Jr.,H.F., Robinson,W.R. & Nebergall,W.H. pp. 1-932. D.C. Heath and Company. Lexington

4: Buch,A. Pure Metals Properties. A Scientific-Technical Handbook
1st edition (1999) Edited by Buch,A. pp. 1-306, ASM International and Freund Publishing House Ltd. Ohio. USA

5: Merck. ChemDAT The Merck Chemical Database Ver. 1.1.5

6: CRC Handbook of Chemistry and Physics
75th edition (1994) Edited by Lide,D.R. , CRC Press Inc. Boca Raton, USA

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© Michael Pilgaard
Created: October 3, 2008
Last update: October 10, 2008