Manganese

From Sciencemadness Wiki
Jump to: navigation, search
Manganese,  25Mn
General properties
Name, symbol Manganese, Mn
Appearance Silvery-gray solid
Manganese in the periodic table
-

Mn

Tc
ChromiumManganeseIron
Atomic number 25
Standard atomic weight (Ar) 54.938044(3)
Group, block , d-block
Period period 4
Electron configuration [Ar] 3d5 4s2
per shell
2, 8, 13, 2
Physical properties
Silvery-gray
Phase Solid
Melting point 1519 K ​(1246 °C, ​2275 °F)
Boiling point 2334 K ​(2061 °C, ​​3742 °F)
Density near r.t. 7.21 g/cm3
when liquid, at  5.95 g/cm3
Heat of fusion 12.91 kJ/mol
Heat of 221 kJ/mol
Molar heat capacity 26.32 J/(mol·K)
 pressure
Atomic properties
Oxidation states 7, 6, 5, 4, 3, 2, 1, −1, −2, −3 ​acidic, basic or amphoteric; depending on the oxidation state
Electronegativity Pauling scale: 1.55
energies 1st: 717.3 kJ/mol
2nd: 1509.0 kJ/mol
3rd: 3248 kJ/mol
(more)
Atomic radius empirical: 127 pm
Covalent radius Low spin: 139±5 pm
High spin: 161±8 pm
Miscellanea
Crystal structure ​​body-centered cubic (bcc)
Speed of sound thin rod 5150 m/s (at 20 °C)
Thermal expansion 21.7 µm/(m·K) (at 25 °C)
Thermal conductivity 7.81 W/(m·K)
Electrical resistivity 1.44 Ω·m (at 20 °C)
Magnetic ordering Paramagnetic
Young's modulus 198 GPa
Bulk modulus 120 GPa
Mohs hardness 6
Brinell hardness 196 MPa
CAS Registry Number 7439-96-5
History
Discovery Torbern Olof Bergman (1770)
First isolation Johann Gottlieb Gahn (1774)
· references

Manganese is a chemical element with symbol Mn and atomic number 25. It is a transition metal, often used in various steels and more often in chemistry, due to its large number of oxidation states.

Properties

Chemical

Manganese slowly tarnishes in air or in water containing dissolved oxygen.

Manganese reacts with all halogens, and most strong acids.

Manganese has 10 oxidation states, though the most common ones are +2, +3, +4, +6, and +7. Manganese compounds in oxidation state +7 are strong oxidizers.

Physical

Manganese is a silvery-gray metal, which has similar properties to iron. It is hard and very brittle. It melts at 1246 °C and boils at 2061 °C. It has a density of 7.21 g/cm3, being slightly less dense than iron.

Availability

Manganese metal is sold by various chemical suppliers. Manganese samples can also be bought from eBay and Amazon.

Isolation

Manganese metal can be extracted from manganese dioxide, readily found in many zinc-carbon batteries. The oxide can be reduced in a thermite reaction with aluminium or even magnesium, although carbon can also be used.

3 MnO2 + 4 Al → 3 Mn + 2 Al2O3
MnO2 + C → Mn + CO2

The reaction with aluminium is exothermic enough to reach the boiling point of manganese. Manganese lumps is somewhat difficult to separate from the the resulting slag. A fluxing agent such as calcium fluoride should be added, which also acts as heat sink.

Better results can be obtained by replacing manganese dioxide with manganese(II,III) oxide (Mn3O4).

Manganese can also be extracted from manganese steels (mangalloy) by dissolving it in an acid, separating the manganese salt and reducing it to manganese metal through various methods.

Projects

Handling

Safety

Manganese is an essential trace element for all known living organisms, however in large quantities has neurotoxic effects. It can cause a poisoning syndrome in mammals, especially when inhaled, leading to severe if not irreversible neurological damage.

Storage

Bulk manganese metal can be stored in any container, away from any corrosive vapors. Powdered manganese should be kept in sealed containers.

Disposal

Manganese compounds should be converted to insoluble or less harmful compounds, such as manganese(II,III) oxide.

References

Relevant Sciencemadness threads