Why is Mn3 + a good oxidizer
VII. Subgroup / 7. Group / manganese group
The most important manganese minerals are the oxides hausmannite (Mn3O4, Fig. 9.7.1.), Braunite (Mn2O3) and pyrolusite (MnO2, 'Braunstein', Fig. 9.7.2.).
|9.7.1. Hausmannite, Mn3O4 (Octahedron, spinel structure)||9.7.2. Pyrolusite, MnO2 (Gremmelsbach, Triberg, Black Forest)|
|9.7.3. Manganese tuber (USA, 1,000 miles southeast of Hawaii, from a depth of 5,000 m)|
Elemental manganese is one of the few metallic elements that shows its own unusual and very complex crystal chemistry. Two of the three modifications have rather complicated cubic structures, which are described in detail here.
|Fig. 9.7.4. elemental manganese|
Four oxidation states of manganese can be seen in the gradual reduction of permanganate (manganate (VII) with perborate:
|⚗ Reduction of permanganate|
| With perborate (NaBO2 . H2O2 . 3 H.2O) permanganate can be gradually reduced: |
The thermodynamic stability of the various oxidation states, which, like the species itself, depends heavily on the pH value of the solution, is shown in the Frost diagram in Fig. 9.7.5. (left). In the Pourbaix diagram (see Fig. 9.7.5. Right, for c= 1 mol / l) the species that are stable at the respective potentials and pH values are also shown. (! Attention: these diagrams depend on the concentrations of the solutions and are based on thermodynamic data!)
|9.7.5. 'Frost' diagram of Mn at pH 0 (red) and pH 14 (blue) (left) ‣SVG and 'Pourbaix' diagram (right) ‣SVG|
It is clear from the two diagrams that Mn is present in low oxidation states under basic conditions in the form of the sparingly soluble oxides / hydroxides. Only at extreme pH values does Mn (II) dissolve in the form of a hydroxido complex (green field in the Pourbaix diagram). Compounds with manganese in higher oxidation states have a strong oxidizing effect in acid. Under basic conditions (see experiment above) all oxidation states from Mn (VII) to Mn (IV) are available, while the light blue manganate (V) is unknown in acidic solutions. In the acidic Mileu, Mn (II) in particular (in the form of the hexaqua complex) is very stable, while under basic conditions Mn (IV) in the form of manganese dioxide is the most stable species, and thus mostly the end product of redox reactions (see analytics, e.g. at manganometry).The + II oxidation state is relatively stable with manganese, since all five are here d-States are simply occupied (d5-Electronic configuration). Transitions between the d-Levels are thus spin-forbidden, so that d-dTransitions do not play a role for the colors of the salts and complexes and many Mn (II) compounds only show a very pale color (mostly slightly pink) at most.
- The hydroxide precipitates out of Mn (II) -containing solutions when ammonia is added (see analysis!):
MnSO4 + 6 NH3 ⟶ Mn (OH)2 + Well2SO4which is insoluble in alkalis.
- The anhydride for this is the monoxide MnO, which has a NaCl structure.
- Manganese (II) forms with NH3 a hexammine complex:
Mn2+ + 6 NH3 ⟶ [Mn (NH3)6]2+
- With H2O2 oxidation to Mn (IV) produces brown-black precipitates of the oxide-hydroxide:
MnII(OH)2 + H2O2 ⟶ MnIVO (OH)2
- Other poorly soluble compounds of Mn (II) are the carbonate and the pale pink (see analysis) colored sulfide:
Mn2+ + CO32- ⟶ MnCO3 Mn2+ + S2- ⟶ MnSIn terms of color, this is NEVER the sulphide in life!
- Well-known oxygen compounds and minerals with manganese in the + III oxidation state are Braunite, Mn2O3, and the mixed valence hausmannite (Mn3O4, see Fig. 9.7.1).
- The hausmannite crystallizes in the spinel structure and contains a MnII- and two mnIIIIons per formula unit. It is a normal spinel, the octahedron is MnIII Jahn-Teller are distorted.
- α-Mn2O3 crystallizes in the C-type structure (also Bixbyit or defect anti-CaF2-Type). Here the Mn2+-Cations form a cubic closest packing of spheres and the oxide ions occupy 3/4 of the tetrahedral holes (cubic, space group Ia3, with magnetic order pseudo-cubic Pbca).
- The black γ form of Mn2O3 is isotypic to γ-Al2O3 and γ-Fe2O3 (Defect spinel) and, like this, is created when the hydroxides are carefully dehydrated.
- Other compounds are MnO (OH) (manganite) and complexes such as [MnF6]3-.
- The pigment 'Manganese Violet' is an ammonium Mn (III) pyrophosphate NH4Mn [P2O7] (see Fig. 9.7.6.). It is used in cosmetics and painting.
9.7.6. Mn violet: NH4Mn [P2O7]
MnO2 is also a very strong oxidizing agent (see analytics, see Frost diagram in Fig. 9.7.5) and can, for example, release chlorine from HCl:
|9.7.7. Mn blue: BaSO4: MnVI|
The permanganate ion is itself a strong oxidizing agent, which under alkaline conditions turns into manganese dioxide MnO2, in acidic conditions to the Mn2+ is reduced. For example, sulphurous acid can be oxidized to sulfuric acid and iodide to iodine. Synproportionation reactions of Mn (VII) and Mn (II) lead to Mn (IV):
|⚗ Mn flashes|
|Small crystals of potassium permanganate are concentrated on the interface between. Sulfuric acid (below) and absolute ethanol (above). The resulting green oil is Mn2O7, the anhydride of permanganic acid, which reacts with explosive decomposition.|
Radio element (artificial element, produced during nuclear fission). Chemically very similar to rhenium.
Rhenium comes together with molybdenum in molybdenite MoS2 in front. It is represented by the reduction of the oxides or sulfides with hydrogen or electrolytically. It crystallizes in a hexagonal close packing of spheres and is used in alloys for thermocouples and filaments (because of its high melting point). The +7 oxidation state is fairly stable. re2O7 can be distilled from an oxidizing medium, i.e. it is largely covalent. The oxide ReO3, the namesake of a very simple and basic structure type, is red. Oxides, sulfides and halides are also well characterized by oxidation states IV, V and VI, but less stable than the above-mentioned oxides. ReCl3 contains clusters with a Re3-Triangle, [Re2Cl8]2- the famous Re-Re quadruple bond.
Typical reactions with perrhenates, [ReO4]- are:
- How difficult is a doctorate
- Is chemical engineering chemistry plus mechanical engineering
- The Europeans hate the Arabs
- What's the worth of me
- What is the name of the Japanese rugby team
- What is your unpopular opinion about love
- German culture favors introverts or extroverts
- Works Adobe on Mac
- Is of a preposition or not
- How many missions landed on Mars
- What is the longest penalty shootout of all time
- Which party has violated the Oslo Agreement?
- What is the difference between supplication
- Hated Queen Diana
- How websites upload pirated content
- Where is blood actually produced?
- How can you tell advertising from propaganda?
- The Vietnamese language is copied from French
- Do people really need cosmetics
- How is summer in Medellin Colombia
- Was the Assassin's Creed real
- Who is Prabhat Choudhary
- How do I make the YouTube channel known
- What sets Keanu Reeves apart from other celebrities