School Science Lessons
2018-11-04
Please send comments to: J.Elfick@uq.edu.au

Chemistry Mn
Table of Contents
Manganese, Mn
Manganates, permanganates
Manganate, MnO42, manganate (VI)
Decomposition of manganates: 3.30.17
Potassium permanganate, KMnO4
Prepare manganates, MnO42-: 12.8.2

Manganese, Mn
See: Manganese Elements, Compounds, (Commercial)
Manganese, Table of Elements
Manganese, Properties
Manganese deficiency in soil: 1.7.0
Manganese and manganese deficiency symptoms: 1.7.0
Manganese compounds
Prepare manganates: 12.8.2
Reactions of manganese (II) salts: 12.8.1
Tests for manganese, benzidine test: 12.11.3.23 (See 2.)

Bustamite, MnCaSiO6: 35.3.3.1
Coronadite, Pb2Mn8O16: 35.20.12
Garnet (Mn3, Al2, Si3, O12): 35.3.3.3
Magnesite, bitter spar, MgCO3
Mancozeb (fungicide): 16.6.13
Maneb (fungicide): 16.6.14
Manganin, resistance alloy, 86% Cu, 12% Mn, 2% Ni, low temperature
Rhodochrosite, MnCO3, 35.20.35
Rhodonite, MnSiO3: 35.20.36.

Manganese
Manganese, Mn (Greekmagnesia, mineral from Magnesia, then altered) (cutaval, colloidal manganese), sheet, foil, granules,
powder (flammability hazard)
Manganin, alloy, 13-18% manganese, 1.5-4% nickel, in resistor
Manganese is a white-grey colour, very hard, brittle transition metal, available as electrolytic flake and manganese (IV) oxide
(manganese dioxide) extracted by electrolytic treatment of ores, e.g. pyrolusite (manganese (IV) oxide) used in ferromanganese for
alloy steel manufacture.
Manganese is a cofactor for many enzymes, but magnesium can usually substitute for it.
The properties of manganese are similar to iron, but manganese is harder, more brittle but less refractory.
It is used to produce ferromanganese to improve hardness, stiffness, and strength of carbon steel, stainless steel, high temperature steel,
and tool steel, also in non-ferrous alloys with aluminium, magnesium, copper and zinc.
Atomic number: 25, Relative atomic mass: 54.9380, r.d. 7.20, m.p. = 1244oC, b.p. = 2100oC, S.G. 7.2 to 7.4
Specific heat capacity: 477 J kg-1 K-1.

Manganese compounds
Alkaline battery, rechargeable alkaline-manganese battery, RAM battery: 15.6.13
Pigments: Mars brown, burnt umber, raw umber, manganese blue, manganese violet and black 14 are Toxic.
Manganese salts, Reactions of manganese (II) salts: 12.8.1
Manganese exists mostly in the (II) oxidation state in natural compounds.
Manganese (II) acetate tetrahydrate, brown crystals, soluble in alcohol and water, decomposes in cold water, used in textile dyeing,
fertilizers, food packaging, feed additives, paints and varnishes.
Manganese (II) carbonate
Manganese (II) chloride
Manganese (II) nitrate, manganese (II) nitrate tetrahydrate, Mn(NO3)2.4H2O, colourless or pink solid crystals, used for colour agent
in porcelain, catalyst, production of manganese dioxide
Manganese (II) sulfate
Manganese (III) acetylacetonate
Manganese alum, MnAl2(SO4)4.22H2O, Apjohnite mineral
Manganese aluminium silicate (Mn3Al2Si3O12), Mn3Al2[SiO4)3, garnet, spessartine, spessa rtite
Manganese aluminium silicate: 35.3.3.3
Manganese gluconate, manganese gluconate dihydrate, MnC12H22O14, light pink powder or coarse pink granules, soluble in water,
insoluble in alcohol and benzene, and used for feed additive, dietary supplement.
Manganese oxides
Manganese silicate, rhodonite: 35.20.36
Manganous chromate, red-brown pigment
Heat potassium chlorate: 17.3.11
Hydrogen peroxide decomposition: 17.3.1.2
Hydrogen peroxide, rate of reaction, suds: 17.1.5
Prepare chlorine: 13.4.1.0.

Manganese (II) carbonate
Manganese (II) carbonate, pink-white hygroscopic powder, S.G. 3.1, decomposes before melting point, soluble in dilute acid, insoluble
 in water, alcohol, ammonia.
Used as pigment, drier for varnishes, medications, plant nutrient, pharmaceuticals, animal feeds, ceramics.
Low cost: from pottery supplies stores
Manganese carbonate, rhodochrosite: 35.20.35

Manganese (II) chloride
Manganese (II) chloride, manganese (II) chloride tetrahydrate (test for chromium), Toxic if ingested
Manganese chloride, pink cubic hygroscopic crystals, soluble in water and alcohol, insoluble in ether, deliquescent.
Used for catalyst in chlorinating of organic compounds, dietary supplement, food additive, animal feed, paint dryers, fertilizers, dyeing,
disinfecting, purifying natural gas, dry cell batteries.

Manganese (II) sulfate
Manganese (II) sulfate, MnSO4, manganese (II) sulfate monohydrate, manganous sulfate, pink powder
Manganese (II) sulfate hydrated, MnSO4.H2O, Toxic if ingested
Manganese (II) sulfate monohydrate, MnSO4.H2O, For 0.1 M solution, 16.9 g in water
Manganese sulfate, red or pale red slightly efflorescent crystals, soluble in alcohol, insoluble in ether.
Used for glazes, varnishes, ceramics, dyeing, fertilizers, fungicides, ore flotation, in medicines and as a nutritional supplement.

Manganese oxides
Manganese (II) oxide, MnO, manganous oxide, manganosite
Manganese (II, III) oxide, Mn3O4, manganese tetroxide, insoluble in water, soluble in hydrochloric acid, mineral hausmannite
Manganese (III) oxide, Mn2O3, dark brown
Manganese (IV) oxide, manganese dioxide, MnO2, black crystalline solid or powder, soluble in acids and ammonium chloride, insoluble
in water, inert to most acids except when heated, forms chlorine with hot HCl
Manganese (IV) oxide, MnO2, manganese dioxide, pyrolusite, manganite, Toxic if ingested
Manganese (IV) oxide, Solution / mixture of 25%, Not hazardous
Manganese (VII) oxide, manganese heptoxide, risk of explosion, Not permitted in schools
Manganese (VII) oxide, Mn2O7
Manganese oxide, green cubic crystals or green powder.
Used for textile printing, ceramics, paints, coloured glass, animal feeds, fertilizers, welding, food additive, dietary supplement, catalyst
in production allyl alcohol.

Manganese (IV) oxide
Manganese (IV) oxide, MnO2, manganese dioxide, manganese black, manganese dioxide, "black oxide of manganese", in pyrolusite,
black powder resembling carbon in appearance.
Manganese (IV) oxide can be distinguished from carbon because it does NOT burn away when heated on a metal lid, forms a
wine-coloured borax bead (catalyst, oxidizing agent, depolarizer in dry cells, e.g. flashlight batteries).
Used as catalyst for decomposition of hydrogen peroxide.
Do NOT use for thermal decomposition of potassium chlorate.
Hydrated manganese oxide in some medicines for schizophrenics and diabetics.
Industrial use in the preparation of chlorine gas and as a catalyst in the preparation of oxygen.
Common names: Pyrolusite (in some dry cell batteries.)

12.8.1 Reactions of manganese (II) salts
1. Add drops of yellow ammonium sulfide solution to manganese (II) chloride solution.
Note the pink precipitate.
Mn2+ + S2- --> MnS (s)
This same precipitate occurs if you pass hydrogen sulfide into an alkaline solution of a manganese (II) salt,
but no precipitate occurs with an acidic solution.

2. Drop sodium hydroxide solution into manganese (II) chloride solution.
Note the white precipitate of manganese (II) hydroxide that rapidly turns brown due to atmospheric oxidation.
Keep on adding the sodium hydroxide solution and note that the precipitate is not soluble in excess.
Mn2+ + 2OH- --> Mn(OH)2 (s)
2.1. Repeat (2.) using ammonium hydroxide with same observations.
2.2. Repeat (2.) after first adding 2 cc of solid ammonium chloride to the manganese (II) chloride solution.
No precipitate occurs.
The ammonium ion introduced depresses the ionization of the hydroxide.

3. To 1 cc of manganese (II) chloride solution, add 1 mL of sodium hydroxide solution, then 2 mL of bromine water or sodium peroxide
and heat.
The valence 2 oxide or hydroxide is oxidized to the higher valence 4 oxide.
manganese dioxide, that forms a dark brown precipitate.
The permanganate forms if the manganese (II) salt is heated with excess oxidizing agent.
Boil some of the manganese (II) chloride
solution with a 2 cc of lead dioxide and 1 mL of concentrated nitric acid.
Dilute with water and filter.
The solution comes through showing the pink permanganate colour.

12.8.2 Prepare manganates
Heat on a crucible lid a piece of potassium hydroxide, crystals of potassium nitrate and some manganese dioxide until the whole mass
has fused.
Leave to cool and add some water and filter.
A deep green solution of potassium manganate forms.
The O2 comes from the KNO3.
4KOH + 2MnO2 + O2 --> 2K2MnO4 + 2H2O
The solution is unstable and is readily hydrolysed by dilute acids and even by largely diluting the solution into a permanganate.
3K2MnO4 + 2H2O --> 2KMnO4 + MnO2 + 4KOH
Dilute the green solution ten times with water and boil.
Note the pink colour of the permanganate on allowing the solution to settle.