School Science Lessons
2019-07-27
Please send comments to: J.Elfick@uq.edu.au

Chemistry Aluminium
Table of Contents
Aluminium
Alums

Aluminium, Al
See: Aluminium Elements, Compounds, (Commercial)
Aluminium, Table of Elements
Aluminium, properties: 7.2.2.1
Aluminium can, beverage can:
Aluminium compounds
Aluminium powder (Safety)
Aluminium foil electroscope: 31.3.8 (Physics)
Aluminium powder bounces: 31.7.16 (Physics)
Aluminium reactions: 12.1.0
Aluminium toxicity: 3.6.1
Anodize aluminium: 15.1.8
Beverage can composition: B1
Corrosion of aluminium: 15.3.15
Dilute sulfuric acid with aluminium: 12.3.3.1
Heat aluminium foil to form aluminium oxide: 8.2.11
Movement of suspended aluminium powder: 3.3.5
Prepare potash alum from its constituent salts: 12.14.1
Prepare potash alum with aluminium foil: 12.14.2
Soda alum, Na2SO4.Al2(SO4)3.24H2O
Recycle aluminium drink-can as potassium aluminium sulfate, alum: 12.7.3.1
Tests for aluminium: Tests.

Aluminium powder
Safety Aluminium powder
Aluminium powder bounces: 31.7.16 (Electric fields and potential)
Movement of suspended aluminium powder: 3.3.5.

Aluminium compounds
Artificial magnets, ferrite magnets: 29.4.72
Alnico magnets
Alumina, aluminium oxide
Alumina, anti-bumping, granules, boiling chips, fused alumina, flower pot bits
Alumina, alumina polishing powder
Aluminium acetate, Al (COOCH3)3, aluminium ethanoate
Aluminium ammonium sulfate, Harmful if ingested
Aluminium ammonium sulfate (dodecahydrate), AlNH4(SO4)2.12H2O, ammonium alum, food additive, E523, buffer, stabilizer
Aluminium bromide, anhydrous, Toxic if ingested or skin contact
Methanides, aluminium carbide, Al4C3
Aluminium chloride
Aluminium fluoride
Aluminium hydroxide
Aluminium nitrate
Aluminium orthophosphate
Aluminium oxalate, Harmful if ingested
Aluminium oxide, Al2O3, alumina
Aluminium phosphide, rat poison, used in ships
Aluminium potassium sulfate
Aluminium sulfate.

12.1.0 Aluminium reactions
Experiments
12.1.10 Alumina as a catalyst in the cracking process
12.1.8 Aluminium chloride with water
12.1.7 Aluminium sulfate reactions
12.1.1 Aluminium with acids
12.1.2 Aluminium with sodium hydroxide
12.1.6 Aluminium with sulfur
12.1.9 Bauxite digestion
12.1.4 Burn aluminium in oxygen
12.1.3 Iodine with aluminium
12.1.5 Thermite reaction, thermit welding.

Tests for aluminium
Heat substances with charcoal and fusion mixture: 12.11.3.8 (See 1.)
Tests for aluminium: 12.11.3 10
Tests for aluminium compounds: 12.13.1
Tests for aluminium compounds in solution: 12.11.3.9.

7.2.2.1 Aluminium properties
1. Aluminium, Al (Latin alumen bitter salt, referring to alum), (US Aluminum), Aluminium ion, Al3+.
In 1990, The International Union of Pure and Applied Chemistry (IUPAC) confirmed the use of the spelling "aluminium", but people
in the US are accustomed to using the spelling "aluminum".
Aluminium is a silver, light, ductile, malleable, metal, with mechanical strength.
Aluminium compounds are abundant.
Aluminium is extracted by electrolysis from the main aluminium ore bauxite dissolved in cryolite.
Bauxite is 8% of the earth's crust so aluminium is the most abundant element in the Earth's crust,
Atomic number: 13, Relative atomic mass: 26.9815, r.d. 2.70, m.p. = 660oC, b.p. = 2470oC, E 173
Specific heat capacity: 900 J kg-1 K-1.

2. Availability
Aluminium, Al, metal filings, ion Al3+, granules (stabilized), pellets (coated) (powder 1396), Flammable powder.
Aluminium is available as foil, sheet, and wire.
Aluminium ignots, 99.7% purity.
Aluminium reagent test kit, No. 1 tablets, No. 2 tablets, AAS Std, leaf, flakes, sheet, "Alfoil" cooking foil, drink-can, ingot, wire,
aluminium foil, 300 width × 150 m roll, "Alfoil" disposable containers, rectangular 120 mm × 175 mm, round 120 mm diameter.
Aluminium, although toxic, is not a heavy metal.
Low cost: aluminum kitchen foil, aluminum drink cans (beverage cans, plastic coated inside), aluminum window screen frames
Duralumin, alloy of Al + Cu + Mg.

3. Uses
1. Aluminium metal is not tarnished in air because it forms protective oxide that prevents further oxidation.
The aluminium foil used in home kitchens from grocery stores and the aluminium wire and aluminium sheeting from hardware stores are
all pure aluminium.
Most reactions of aluminium are inhibited by a surface coating of aluminium oxide.
This is the reason that such an active metal as aluminium can be used widely for construction and for containers.
Alfoil disposable containers + lid, 105 mm width × 184 mm depth × 38 mm height
Aluminium foil is used to to clean pots and barbecue grill on picnics. Rub rust from and polish chromium plating, seal used paint tins
and planting pots, catch baking drips.
Aluminium is protected by layer of oxide that can be thickened if an anode in electrolytic cell, i.e. anodized then can be coloured,
malleable, low density, used in "Alfoil" cooking foil, drink-cans, saucepans, cars, duralumin (alloy of Al + Cu, Mg), for aircraft bodies
and struts, motor vehicle parts.
Aluminium food additive, E173 (colour: metallic) (Banned, some countries, excess unsafe).

4. Reactions
Aluminium reacts with dilute HCl or H2SO4 to form H2 and metal ion, with concentrated oxidizing acids, HNO3 or H2SO4 to
produce high oxidation number ions, and sulfur dioxide SO2 or nitrogen dioxide, NO2, with steam to give the oxide and hydrogen gas.
Heated powder forms oxide.
Excess aluminium may cause short term toxicity, e.g. aluminium sulfate in drinking water, corroded cooking utensils used for cooking
acidic foods, alum treatment of water.

5. Safety
�Aluminium powder is not safe for school use, so it is not supplied as powder.
So to avoid explosive reactions, do not grind aluminium metal to powder.
Finely divided aluminium particles (powder or fine turnings) burn in air with an intense white flame if ignited.
A significant amount of ultraviolet radiation is emitted, and the flame should not be watched with the naked eye.
Unoxidized aluminium powder reacts vigorously with both concentrated acids or alkalis to yield hydrogen gas, which is explosive when
mixed with air.
The reaction may occur with such vigour that the aluminium particles and acid or alkali may be ejected from the container.
Aluminium metal reacts violently with halogens (chlorine, bromine, iodine).
The reaction of aluminium with liquid bromine is hazardous and should not be attempted.

Aluminium compounds in solution tests
Put 2 drops of cobalt chloride solution (red) on a piece of filter paper.
The drop 2 drops of aluminium sulfite solution of the filter paper.
Hold the filter paper over a small flame, then ignite it over a saucer.
A blue ash indicates aluminium compounds.

Aluminium oxide, alumina
Aluminium oxide, Al2O3, alumina, corundum, amphoteric oxide, almost insoluble in water (used for leaching minerals), lung irritation,
Toxic if inhaled, alumina (porcelain), amphoteric, corundum (hardness 9, abrasive, sand paper, in red ruby, in blue sapphire),
diamantine, emery powder (abrasive), corroded aluminium (bauxite, hydrated aluminium oxides Al2O3.nH2O + laterite), alumina
hydrate for craft, alumina has amorphous or crystalline state in corundum and bauxite powder used for thin-layer chromatography plates.
Low cost purchase from pottery supplies store.
Amphoteric oxides react with both acids and bases, e.g. Al2O3, PbO, SnO, ZnO.
Their hydroxides are also amphoteric.

Aluminium chloride, AlCl3
Aluminium chloride, AlCl3, anhydrous, covalent, Toxic if ingested
Aluminium chloride, Solution < 5%, Not hazardous
Aluminium chloride, hydrated, AlCl3.6H2O, the anhydrous AlCl3 is covalent, for 0.1 M solution, 24 g of hydrated salt in 1 Litre water
Fireproof cloth: 3.5.11 (See: 2.)
Aluminium chloride with water: 12.1.8.

Aluminium hydroxide
Aluminium hydroxide (1-water), bauxite (antacids) 500 g, E173 (food additive)
Alkalis with amphoteric oxides and hydroxides: 12.7.7
Bauxite digestion: 12.1.9.

Aluminium nitrate
Aluminium nitrate, hydrated aluminium nitrate, aluminium nitrate nonahydrate, Al(NO3)3.9H2O, Harmful if ingested, crystals , lumps,
white, soluble in water, used in tanning, antiperspirants, inhibit corrosion
Aluminium nitrate with sodium hydroxide
Al(NO3)3 + 3NaOH --> Al(OH)3 + 3NaNO3.

Alums
The original "alum" was the hydrated double salt of aluminium and potassium with colourless octahedral crystals and an astringent taste,
used for mordants before dyeing cloth.
Later the term "alum" was used to describe similar double sulfates where other elements, or radicals replaced aluminium or potassium.
So an "alum" is a hydrated aluminium potassium sulfate and related minerals.
Some plants with astringent roots are called "alum roots".
Aluminium ions form alums that are complex hydrated metal sulfates that contain 12 or 24 H2O.
Aluminium potassium sulfate is a buffer and firming agent, E522.
Ammonium alum, AlNH4(SO4)2.12H2O.

Aluminium potassium sulfate
Prepare chrome alum: 12.14.4.0
Prepare iron (III) ammonium alum (NH4)2SO4.Fe2(SO4)3.24H2O: 12.14.3
Potassium alum, "alum", Toxic if ingested
Potassium aluminium silicate, E555: 35.15.0
Potassium aluminium sulfate, aluminium potassium sulfate, alum, potash, potash alum
Potash alum, aluminium potassium sulfate, KAl(SO4)2.12H2O
Potassium salts
Prepare chrome alum: 12.14.4
Prepare potash from ash: 5.40
Prepare potash alum: 12.14.1
Prepare potash alum with aluminium foil: 12.14.2
Potassium alum, "alum", potash alum, potassium aluminium sulfate,
Al2(SO4)3.K2(SO4).24H2O, K2SO4.Al2(SO4)3.24H2O, KAl(SO4)212(H2O)
Artificial gemstones: 12.10.2.6.1
Fireproof cloth: 3.5.11 (See 2.)
Kalinite, Aluminium potassium sulfate
Potassium alum and clay suspensions: 7.6.2.2
Prepare invisible inks: 4.19
Prepare potash alum from its constituent salts: 12.14.1
Prepare potash alum with aluminium foil: 12.14.2
Prepare self-leavened flour, "self-raising flour": 19.1.8.1
Recycle aluminium drink-cans as potassium aluminium sulfate, alum: 12.7.3.1.

Ammonium alum, NH4Al(SO4)2.12H2O, Tschermignite
Potassium aluminium sulfate, aluminium potassium sulfate, alum, aluminium potash, potash alum
Soda alum, Na2SO4.Al2(SO4)3.24H2O
luminium potassium sulfate
Alum, potassium alum, "common alum", potash alum, hydrated potassium aluminium sulfate, hydrated aluminium potassium sulfate,
aluminium potassium sulfate 12-hydrate, kalinite, a double sulfate of aluminium, the "alum" sold at grocery shops.
Aluminium potassium sulfate is very astringent and is used for purifying water.
Al2(SO4)3.K2(SO4).24H2O or AlK(SO4)2.12H2O or
KAl(SO4)2.12H2O.
The original "alum" was the hydrated double salt of aluminium and potassium with colourless octahedral crystals and an astringent taste,
used for mordants before dyeing cloth.
Later the term "alum" was used to describe similar double sulfates where other elements, or
radicals replaced aluminium or potassium.
So an "alum" is a hydrated aluminium potassium sulfate and related minerals.
Some plants with astringent roots are called alum roots.
Aluminium ions form alums that are complex hydrated metal sulfates that contain 12 or 24 H2O.
Aluminium potassium sulfate is a buffer and firming agent, E522.
Ammonium alum, AlNH4(SO4)2.12H2O.
Chrome alum, chromium (III) potassium sulfate, potassium chromium sulfate, CrK(SO4)2.12H2O or K2SO4.Cr2(SO4)3.24H2O,
for tanning, mordant, photography, purple or violet-red octahedral crystals.

Aluminium silicate, Zeolite, e.g. tetrapropylammonium, (TPA) ZSM-5: 35.20.49
Aluminium sulfate
Artificial magnets, ferrite magnets, "Alnico", "Alcomax": 29.4.72
Bauxite is a mixture of iron and aluminium hydroxides and oxides.
Bauxite: 35.20.5 (Geology)
Bauxite digestion: 12.1.9
Beryl, Be3Al2(SiO3)6
Bentonite, bentonite clay: 35.22.4.4 (Geology)
Copper-aluminium alloys, bronze: 5.5.8
Cryolite, sodium aluminium fluoride, Na3AlF6: 35.20.13 (Geology)
Fuller's earth: 35.22.4.5 (Geology)
Garnet: 35.3.3.3 (Geology)
Halloysite, clay mineral: 35.22.4.7 (Geology)
Illite, clay mineral: 35.22.4.1 (Geology)
Kaolinite, kaolin-type clays: 35.20.21.1 (Geology)
Pegmatite: 35.21.3 (Geology)
Prepare potash alum with aluminium foil: 12.14.2
Stilbite: 35.20.43 (Geology)
Sunstone (Geology)
Tourmaline (Geology)
Tschermignite, NH4Al(SO4)2.12H2O, ammonium alum
Weight of aluminium in aluminium sulfate: 17.6.2
Zeolite: 35.20.4 (Geology).

Aluminium potassium sulfate
Aluminium potassium sulfate-12-water, muddy water: 10.11.1,
Aluminium potassium sulfate-12-water, fireproof paper: 3.5.11 (See 2.)
Aluminium potassium sulfate-12-water, into clay suspension: 7.6.2.2
Aluminium potassium sulfate-12-water, Secret writing inks, alum solution, K2SO4Al2(SO4)3.2H2O: 3.2.5.1
Prepare self-leavened flour, "self-raising flour": 19.1.8.1.

Aluminium potassium sulfate-12-water, aluminium potassium sulfate hydrated, AlK(SO4)2.12H2O, KAl(SO4)2.12H2O
Aluminium potassium sulfate-12-water, potash alum, "alum", aluminium potash
Alum, potassium alum, "common alum", potash alum, hydrated potassium aluminium sulfate, hydrated aluminium potassium sulfate,
aluminium potassium sulfate 12-hydrate, kalinite, a double sulfate of aluminium, the "alum" sold at grocery shops.
Aluminium potassium sulfate is very astringent and is used for purifying water.
Al2(SO4)3.K2(SO4).24H2O or AlK(SO4)2.12H2O or
KAl(SO4)2.12H2O.

Aluminium sulfate
Aluminium sulfate reactions: 12.1.7
Artificial gemstones: 12.10.2.6.1
Dyes with a mordant: 19.5.3 (See 2.)
Potassium alum or aluminium sulfate with clay suspensions: 7.6.2.2
Weight of aluminium in aluminium sulfate: 17.6.2
Zeolite 35.20.49 (Geology).

Aluminium sulfate, Al2(SO4)3, hydrated aluminium sulfate, Al2(SO4)3.18H2O, (NOT "alum"!)
Aluminium sulfate, Al2(SO4)3 xH2O, aluminium sulfate hydrate, cake alum, Harmful to eyes, Harmful if ingested
Aluminium sulfate octadecahydrate, Al2(SO4)3.18H2O, wrongly "alum", E520, foam agent in fire extinguishers, water filter powder,
flocculation agent, food additive E520, modifier, precipitator in sewage treatment, mordant, paper sizing, for 0.l M solution, 66 g of
hydrated salt in 1 L water.

12.1.1 Aluminium with acids
Dissolve aluminium in heated dilute hydrochloric acid and note that hydrogen gas forms.
2Al + 6H + --> 2A13+ + 3H2 (g)
Hot concentrated sulfuric acid will attack aluminium with the production of sulfur dioxide.
Dilute or concentrated nitric acid acts only very slowly on aluminium.

12.1.2 Aluminium with sodium hydroxide
Use aluminium cooking foil or aluminium pie pans.
Use caustic soda drain cleaner from a hardware shop.
Wear safety goggles, gloves, lab coat.
Keep away any matches, sparks, flames.
If exploding hydrogen, wear ear protection.
Be careful! Hydrogen gas forms from the very rapid reaction
1. Use a dropper to put drops of concentrated sodium hydroxide solution onto a sheet of aluminium foil or aluminium powder in a
test-tube.

2. Add 5 g coarse aluminium powder to 20 ml of 40 % sodium hydroxide solution in a test-tube.
Quickly place the test-tube in the bottom of a tall glass beaker before the violent react occurs.
The coarse aluminium powder has a surface layer of aluminium oxide, which is first dissolved by the sodium hydroxide before the main
reaction occurs.
The aluminium completely dissolves and the water acts here too as an acid
(The aluminate ion in an anhydrous compound is shown as AlO2-, and in the hydrated form is shown as Al(OH)4-.)
�2Al (s) + 2NaOH (aq) + 2H2O (l) --> 2NaAlO2 (aq) + 3H2 (g) + energy
2Al + 2OH- + 2H2O --> 2AlO2- + 3H2 (g)
2Al (s) + 2NaOH (aq) + 6H2O --> 2Na+ (aq) + 2[Al(OH)4]- + 3H2 (g)
The following equations show the aluminium reacting with water to form the amphoteric aluminium hydroxide Al(OH)3, which later
goes in solution to produce aluminates, [Al(OH)4]-.
2Al + 6H2O --> 2Al(OH)3 + 3H2
Al(OH)3 + NaOH --> Na+ + [Al(OH)4]-
Al2O3 + 2NaOH + 3H2O --> 2Na+ + 2[Al(OH)4]-
Sold as "drain cleaners", e.g. Drano, contain sodium hydroxide crystals and pieces of aluminium, which react as above when put in
a wet clogged drain.
The reaction is very hot as the sodium hydroxide reacts with fats to form soaps, the hydrogen applies pressure to move the pieces of
aluminium to whirl around and cut the blockage.

3. Stand a clear glass bottle in a container of water.
Do not use a plastic drink bottle.
Add water to the bottle to 1/3 volume and add water to the container so the water levels in the bottle and container are the same.�
Add a small measured amount of caustic soda to the bottle.
Pick up the bottle, dissolve the caustic soda by swirling the bottle, then replace the bottle in the container.
Roll a� sheet of aluminium foil into a tube to fit through the mouth of the bottle.
Attach a balloon to the mouth of the bottle so that it fills with hydrogen gas.
Attach a balloon clip and let the balloon float up in the air.
If the balloon does not float up in the air, because it is not full enough, wait until the bottle has cooled and repeat the experiment with
more caustic soda and aluminium foil.
If the balloon does not float up in the air, and feels heavy, because the reaction has been too vigorous so some water has condensed
in the balloon, wait until the bottle has cooled and repeat the experiment with less caustic soda and aluminium foil.

12.1.3 Iodine with aluminium
Use < 5 g total material of iodine to react with aluminium powder in a fume cupboard.
However, be aware that a cloud of unreacted iodine vapour may be released.
Fine particles of aluminium react violently with iodine, especially after a drop of water has been added.
A large amount of unreacted iodine is liberated as purple vapour into the air.
This reaction should only be done with < 5 g of materials and in a fume cupboard or outdoors.
Mix the ingredients in a small ceramic mortar and pestle.
All observers must wear eye protection.

12.1.4 Burn aluminium in oxygen
Sprinkle aluminium powder onto a Bunsen burner flame or heat aluminium powder in a crucible, then lower it into a gas jar of oxygen.
he aluminium burns brightly to form the white powder magnesium oxide.
4Al (s) + 3O2 (g) --> 2Al2O3 (s)
aluminium + oxygen --> aluminium oxide
Aluminium oxide is an amphoteric oxide that does not dissolve in water.
Stored aluminium is always coated with aluminium oxide, which protects it from most chemical reactions.
So aluminium can be used for many purposes where an unreacted metal is needed.

12.1.5 Thermite reaction, thermit welding
Be careful! The thermite reaction is a hazardous experiment.
Mix aluminium powder or aluminium turnings with iron oxide and ignite the mixture with a burning magnesium ribbon.
Do the experiment in the open with observers at least ten metres away.
Do not use > 25 g of the reaction mixture.
Prepare the reaction mixture in a cut down aluminium beverage can, suspended above a bucket or trough of sand to contain the molten
iron formed.
The mixture may be difficult to ignite, but burns with white heat, producing molten iron that can be tapped from the bottom of the
container.
Be careful! Burning magnesium ribbon held close to the eyes may cause eye damage.
The mixture may react violently if the aluminium particles are too fine.
Any trace of moisture in the reactants or container may cause violent evolution of steam and ejection of the white hot contents.
2Al + Fe2O3 --> 2Fe + Al2O3
8Al + 3Fe3O4 --> 9Fe + 4Al2O3
Thermit welding is used to weld iron rails together
2Al + 3FeO -->3Fe + Al2O3
2Al + Fe2O3 --> 2Fe + Al2O3
The ends of the rails are encased in thermit putty to hold the molten products of the reaction.
The putty consists of silica sand, bentonite, carboxymethyl cellulose and water.

12.1.6 Aluminium with sulfur
Mix dry aluminium powder with twice its volume of sulfur powder.
Put into a test-tube only enough to cover the bottom of the test-tube.
Be careful! Larger quantities may explode! Set up a safety screen.
Clamp the test-tube vertically and heat with a Bunsen burner.
Note the vigorous action where aluminium sulfide is synthesized.
Leave to cool, then add drops of water.
Hydrogen sulfide forms because of the hydrolysis of the aluminium sulfide.
2Al + 3S --> Al2S3
Al2S3+ 6 H2O --> 2Al(OH)3 (s) + 3H2S (g).

12.1.7 Aluminium sulfate reactions
1. Add ammonia solution, NH3 (aq) ("ammonium hydroxide") to aluminium sulfate solution.
Note the white precipitate of aluminium hydroxide that is insoluble in excess ammonia solution.
Al3+ + 3OH- --> Al(OH)3 (s).

2. Add drops of sodium hydroxide to aluminium sulfate solution.
Note the white precipitate that dissolves in excess sodium hydroxide to form sodium aluminate.
Aluminium hydroxide is amphoteric.
Al(OH)3 + OH- --> AlO2- + 2H2O.

3. Add blue litmus solution to aluminium sulfate solution.
The blue litmus turns red.
Add sodium carbonate solution and note the production of carbon dioxide.
Aluminium salts in solution can act as acids because of hydrolysis.
Al3+ + 3H2O --> Al(OH)3 + 3H +.

4. Pass hydrogen sulfide through aluminium sulfate solution to produce the hydroxide, not the sulfide.

5. Mix aluminium sulfate with twice its volume of anhydrous sodium carbonate and heat it on a charcoal block.
Note the white infusible mass.
Add cobalt nitrate solution and heat again.
A bright blue solid forms.

12.1.8 Aluminium chloride with water
Be careful! Demonstrate this reaction only to senior students.
Place < 5 g of aluminium chloride in a beaker in a fume cupboard and add water drop-by-drop.
The material will hiss, crackle and release clouds of hydrogen chloride and fine particles.
Anhydrous aluminium chloride, AlCl3, reacts violently with water to form the hydrated salt by hydrolysis, and a solution of H+ ions and
Cl- ions (a solution of hydrochloric acid) and hydrogen chloride gas.
The formation of an acid solution is more typical of a non-metal rather than a metal and this reflects the position of aluminium to the
right of magnesium in the periodic table.
Fine aerosol particles may also be generated.
Both the hydrogen chloride gas and the fine particles are extremely irritant to the lungs.
Aluminium chloride should only be used in a fume cupboard and only in small amounts.
Do not mix aluminium chloride with alkaline materials, e.g. sodium hydroxide, because a violent reaction may occur.
Aluminium chloride is exceedingly hygroscopic so keep it in a tightly-sealed plastic container.
Purchase the material only in small amounts, e.g. 100 g.
Aluminium bromide, AlBr3, has dangerous properties similar to anhydrous aluminium chloride.
AlCl3 (S) + 3H2O (l) --> Al(OH)3 (s) + 3H+ (aq) + 3Cl- (aq).

12.1.9 Bauxite digestion
An aliquot is a portion, a known fraction of the whole sample.
Wear safety gloves and safety spectacles
Weigh 10 g of ground, dried bauxite and transfer to a reflux flask.
Add 100 mL of 20% sodium hydroxide solution and boil under reflux for 1-2 hours.
Leave to cool, then transfer the solution and residue to a 200 mL volumetric flask.
To make sure all the contents of the reflux are transferred, use demineralized water.
Leave to cool, then make up to volume with demineralized water.
When the muddy residue has settled overnight, remove a 10 mL aliquot to a 250 mL beaker and dilute to 100 mL with demineralized
water.
Heat the mixture until it boils, then make acid with 1:1 HCl using methyl red indicator.
Add 2 g of ammonium chloride, then add 1:1 ammonium hydroxide until the yellow end point is reached.
Boil the mixture to coagulate the precipitate, then filter it while still hot and wash the precipitate on the filter paper with hot water.
Leave the precipitate and filter paper overnight to dry to a slightly damp consistency.
Transfer the precipitate to a weighed crucible, e.g. porcelain, silica or platinum.
Dry the precipitate on the edge of a hot plate.
Do not allow any material to be lost by spitting.
Transfer the crucible and contents to a muffle furnace and ignite to a constant weight at 1, 0000 to 1, 200oC.
Leave the crucible and contents to cool in a desiccator, then weigh them.
Calculate the percentage of alumina in the the bauxite: (weight of crucible and residue - weight of crucible) × 20 × 100 / weight of the
sample.
If the "mud" is left with the solution it contributes to less than 1% of the total volume, an almost insignificant error.
The alumina content can also be determined volumetrically with EDTA.

12.1.10 Alumina as a catalyst in the cracking process
See diagram 12.1.10: Alumina as a catalyst
Large quantities of alumina, aluminium (III) oxide, are used in the cracking processes in oil refineries.
One of the products, ethylene gas, C2H2, is used in the petrochemical industry to produce polyethylene and other polymers.
Activate alumina is very porous and is used as a filter for water treatment, an adsorption desiccant and a catalyst for natural gas and oil
refining processes.

Experiment
Use a fume hood for this experiment.
Hot paraffin oil and ethylene gas are flammable.
Set up the apparatus as in diagram 12.1.10.
See diagram 12.1.10: Alumina as a catalyst
Put 5 cm of paraffin oil and boiling chips in the boiling tube.
Clamp it at a shallow angle, then put 0.5 g of alumina powder half way down the boiling tube.
Replace the stopper.
First heat the alumina strongly with a Bunsen burner, then heat the alumina and paraffin oil alternately until the paraffin oil boils and its
vapour passes over the alumina.
Let the first few bubbles of gas escape under the fume hood, then collect two test-tubes of gas.
Fix stoppers on the test-tubes.
Immediately after collecting the two test-tubes of gas, turn off the Bunsen burner and remove the delivery tube and stopper from under
the boiling tube.
This action prevents water "sucking back" into the boiling tube as it cools.

12.13.1 Tests for aluminium compounds
Put two drops of red cobalt chloride solution on to a piece of filter paper.
Add two drops of aluminium sulfate solution.
Dry the paper by holding it over a flame and then ignite it over a saucer.
The ash is blue.
This is a test for all aluminium compounds in solution.

12.11.3.9 Tests for aluminium compounds in solution
Put 2 drops of cobalt chloride solution (red) on a piece of filter paper.
The drop 2 drops of aluminium sulfite solution of the filter paper.
Hold the filter paper over a small flame, then ignite it over a saucer.
A blue ash indicates aluminium compounds.

12.11.3.10 Tests for aluminium
1. Heat charcoal with fusion mixture, note heated metal appearance.
Aluminium produces a white residue.
Add drops of cobalt nitrate solution and heat again to form a blue mass but this is also caused by fusible phosphates, arsenates, borates
and silicates.

Alnico magnets
Alnico magnets, ferromagnetic alloy, Al 8-12%, Ni 15-26%, Co 5-24% + in some forms Cu 6%, Ti 1%
used to make strong permanent magnets for electric motors, refrigerator doors and radio speakers, used at 500oC to 800oC, conduct
electricity, resist corrosion.