School Science Lessons
2024-12-24
(topicIndexAluminium)
Aluminium, Al
Please send comments to: j.elfick@uq.edu.au
Contents
12.0.0 Aluminium properties
12.1.0 Aluminium compounds
12.2.0 Aluminium compounds, (Geology)
12.3.0 Aluminium experiments
12.4.0 Aluminium powder
Tests for aluminium
12.1.0 Aluminium compounds
12.1.1 Aluminium acetate
12.1.2 Aluminium ammonium sulfate
12.1.3 Aluminium bromide
12.1.4 Aluminium carbide
12.1.5 Aluminiumchloride
12.1.6 Aluminium fluoride
12.1.7 Aluminium hydroxide
12.1.8 Aluminium nitrate
12.1.9 Aluminium oxalate
12.1.10 Aluminium oxide
12.1.11 Aluminium phosphate
12.1.12 Aluminium phosphide
12.1.13 Aluminium potassium sulfate
12.1.14 Aluminium sulfate
12.1.15 Aluminium silicate
12.1.16 Alum
12.1.17 Anti-bumping granules
12.20 Aluminium compounds, (Geology)
12.2.1 Alnico magnets
12.2.2 Bauxite
12.2.3 Cryolite
Feldspars, (Geology)
12.2.5 Kyanite
12.2.6 Stilbite
12.2.7 Zeolite
12.3.0 Aluminium experiments
12.3.1 Alumina as a catalyst in the cracking process
12.3.2 Aluminium chloride with water
12.3.3 Aluminium sulfate reactions
12.3.4 Aluminium with acids
12.3.5 Aluminium with sodium hydroxide
12.3.6 Aluminium with sulfur
12.3.7 Bauxite digestion
12.3.8 Burn aluminium in oxygen
15.1.6 Corrosion of aluminium
12.3.10 Heat aluminium foil
12.3.11 Iodine with aluminium
12.3.12 Tests for aluminium
12.3.11 Tests for aluminium compounds
12.3.12 Tests for aluminium compounds in solution
12.3.15 Thermite reaction
12.0.0 Aluminium properties
See: Aluminium, Table of the Elements
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".
However, 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. = 660 oC, b.p. = 2470 oC, E 173
Specific heat capacity: 900 J kg-1 K-1
Aluminium availability:
Aluminium, Al, metal filings, ion Al3+, granules (stabilized), pellets (coated) (powder 1396), Flammable powder
Aluminium is available as foil, sheet, and wire.
Aluminium foil, "Alfoil" cooking foil, 300 width × 150 m roll, "Alfoil" disposable containers, rectangular 120 mm × 175 mm, round 120 mm diameter.
Aluminium ignots, 99.7% purity
Aluminium reagent test kit, No. 1 tablets, No. 2 tablets, AAS Std, leaf, flakes, sheet, drink-can, ingot, wire
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
Aluminium uses
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 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.
It is malleable, low density, used in "Alfoil" cooking foil, drink-cans, saucepans, duralumin (alloy of Al + Cu, Mg), aircraft bodies and struts, motor vehicle parts.
Aluminium food additive, E173 (colour: metallic) (Banned, some countries, excess unsafe)
Heated powder forms oxide.
Excess aluminium may cause short term toxicity, e.g. aluminium sulfate in drinking water, corroded cooking utensils with acidic foods, alum treatment of water.
12.1.1 Aluminium acetate
Aluminium acetate, Domeboro, C6H9AlO6, Al COOCH3)3, aluminium ethanoate, topical astringent, antiseptic agent.
12.1.2 Aluminium ammonium sulfate
Aluminium ammonium sulfate (dodecahydrate), (AlNH4(SO4)2.12H2O), ammonium alum, food additive, E523, buffer, stabilizer.
12.1.3 Aluminium bromide
Aluminium bromide, AlBrx, commonly aluminium tribromide (Al2Br6), used in Friedel–Crafts reactions for production of polystyrene.
12.1.4 Aluminium carbide
Aluminium carbide, (Al4C3), yellow-brown crystals, reacts with water to give methane.
Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4
12.1.5 Aluminium chloride
Aluminium chloride, (AlCl3), anhydrous, covalent, Toxic if ingested, but 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.
Aluminium chloride with water: 12.1.8
12.1.6 Aluminium fluoride
Aluminium fluoride, aluminum trifluoride, AlF3, odourless white powder, with cryolite used in production of aluminium by electrolysis.
12.1.7 Aluminium hydroxide
Aluminium hydroxide, Al(OH)3, occurs as mineral gibbsite (hydrargillite), E173 food additive, antacid, many biomedical uses.
Prepare aluminium hydroxide precipitate: 7.6.4
12.1.8 Aluminium nitrate
Aluminium nitrate, Al(NO3)3, hydrated aluminium nitrate, aluminium nitrate nonahydrate, Al(NO3)3.9H2O harmful if ingested.
Crystals are white and soluble in water. It is used in tanning, antiperspirants, to inhibit corrosion.
Aluminium nitrate with sodium hydroxide: Al(NO3)3 + 3NaOH --> Al(OH)3 + 3NaNO3.
12.1.9 Aluminium oxalate
Aluminium oxalate, C6Al2O12, strong dicarboxylic acid, occurs in many plants, produced in the human body and excreted in the urine.
12.1.10 Aluminium oxide
Aluminium oxide, (Al2O3), alumina, orundum, 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.
Alumina polishing powder
12.1.11 Aluminium phosphate
Aluminium phosphate, AlO4P, berlinite mineral. used in cake mixes and baking powders, and as an antacid and adsorbent of toxoids.
12.1.12 Aluminium phosphide
Aluminium phosphide, AlP, fumigant, grey-yellow crystalline solid, phosphideis used to destroy pests in grain silos.
It has a strong smell like garlic or rotten fish and should be tranported in the open on the back of a vehicle.
It reacts with water to give very toxic phosphine gas.
AlP + 3 H2O -->Al(OH)3 + PH3
12.1.13 Aluminium potassium sulfate
Aluminium potassium sulfate, potassium aluminium sulfate, alum, aluminium potash, potash alum, Harmful
Potassium aluminium sulfate, aluminium potassium sulfate, alum, potash, potash alum
Potassium alum, "alum", potash alum, potassium aluminium sulfate, Al2(SO4)3.K2(SO4).24H2O, K2SO4.Al2(SO4)3.24H2O, KAl(SO4)212(H2O)
Kalinite, Aluminium potassium sulfate
Aluminium potassium sulfate-12-water Aluminium potassium sulfate-12-water, aluminium potassium sulfate hydrated
Al2(SO4)3.K2(SO4).24H2O or AlK(SO4)2.12H2O or 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
12.1.14 Aluminium sulfate
Aluminium sulfate reactions: 12.3.3
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 called "alum", E520, foam agent in fire extinguishers, water filter powder.
It is used as a flocculation agent, food additive E520, modifier, precipitator in sewage treatment, mordant, paper sizing.
For 0.l M solution, use 66 g of hydrated salt in 1 L water.
Aluminium sulfate with clay suspensions7.6.3
12.1.15 Aluminium silicate
Aluminium silicate, Al2SiO5, fibrous material, mineral andalusite Al2O3·SiO2
12.1.16 Alum
The original "alum" was the hydrated double salt of aluminium and potassium with colourless octahedral crystals and an astringent taste.
It was 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.
"Alum" often refers to potassium alum, potash alum, potassium aluminium sulfate, aluminium potassium sulfate
KAl(SO4)2·12H2O, AlK(SO4)2.12 H2O, KAl(SO4)2, AlK(SO4)2, K2SO4.Al2(SO4)3.24H2O, AlKO8S2.
Soda alum, Na2SO4.Al2(SO4)3.24H2O
Potassium alum, "common alum", potash alum, hydrated potassium aluminium 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 potassium sulfate is a buffer and firming agent, E522.
Other alums:
Ammonium alum, Aluminium ammonium sulfate dodecahydrate, AlNH4(SO4)2.12 H2O, AlH28NO20S2, NH4Al(SO4)2.12H2O, Tschermignite
Sodium alum, Soda alum, Sodium aluminum sulfate dodecahydrate, AlNa(SO4)2· nH2O (n = 0 or 12), AlH24NaO20S2, Na2SO4.Al2(SO4)3.24H2O
Chrome alum KCr(SO4)2·12H2O, CrK(SO4)2.12H2O, K2SO4.Cr2(SO4)3.24H2O, chromium (III) potassium sulfate, potassium chromium sulfate
It is used for for tanning, mordant, photography, purple or violet-red octahedral crystals.
Industrial alum (papermaker's alum) Al2(SO4)3·nH2O
Tschermignite, NH4Al(SO4)2.12H2O, ammonium alum
12.1.17 Anti-bumping granules, boiling chips, alumina
Anti-bumping granules, boiling chips (- ceramic, silicon carbide, fused alumina)
Boiling chips, fused alumina or flower pot bits, prevent large bubbles of gas forming that could cause explosive emissions from a beaker containing heated solution.
Sudden formation of a large amount of vapour from the bottom of a heated vessel of liquid, rather than the usual controlled boiling causes explosions.
So boiling chips (anti-bumping granules) are added to chemical reactions to keep the bubbles small and aid steady boiling.
Hydrocarbons with longer chains have higher boiling points than with branched chains, because of more van der Waals intermolecular bonds between molecules.
12.3.15 Thermite reaction
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.
12.3.10 Heat aluminium foil
Heat aluminium foil to form aluminium oxide
Aluminium foil (al-foil, alu-foil, "Reynolds wrap'), has thickness usually < 0.2 mm.
It is shiny on one side and matte on the other side, caused by the rolling process of manufacture.
Heat a piece of aluminium cooking foil or a "silver" milk bottle top.
Describe what happens to the aluminium foil.
You may not see any changes, because aluminium does not change colour when heated.
The melting point is 655 oC to 660 oC.
When white hot, it slowly forms a coating of aluminium oxide, alumina.
Do not heat aluminium powder.
If not pure, it may explode.
4Al (s) +3O2 (g) --> 2Al2O3 (s)
aluminium + oxygen --> aluminium oxide.
12.2.1 Alnico magnets
Alnico magnets, ferromagnetic alloy, contains Al 8-12%, Ni 15-26%, Co 5-24% + in some forms Cu 6%, Ti 1%.
It is used at 500 oC to 800 oC to make strong permanent magnets for electric motors, refrigerator doors and radio speakers.
12.2.2 Bauxite
Bauxite, Al2O3 x2H2O, (hydrated aluminium oxide, Al2O3), is a residual sedimentary mineral.
It contains alumina and other oxides of aluminium in the amorphous or crystalline state.
So it is more a rock-like mixture than a mineral.
Bauxite is a mixture of iron and aluminium hydroxides and oxides.
It is usually formed by weathering in tropical regions.
It is the most important ore for production of aluminium.
Bauxite has non-metallic lustre, white streak, no good cleavage, can be scratched by the finger nail, white to brown grey colour, uneven fracture, specific gravity 2.0-2.5.
12.2.3 Cryolite
Cryolite, sodium aluminium fluoride, Na3AlF6, has colourless to white to yellow colour, and sometimes purple to black colour.
It has Mohs scale of hardness 2.5-3, white streak, greasy to glassy lustre, no cleavage, uneven fracture and specific gravity 2.95-3.0.
The refractive index is 1.34. so the specimen almost disappears in water.
It is a colourless rare mineral used as a flux in electrolytic production of aluminium from bauxite, and is manufactured synthetically.
Note the disappearance in water, no salty taste and density of the specimen.
12.2.5 Kyanite
Kyanite, Al2(O, SiO4), disthene, munkrudite, cyanite, rhaeticite (white grey kyanite), (Greek kyanos blue), is an aluminosilicate mineral.
Mohs scale of hardness 4-5 and 6.5-7 depending on the direction of the cleavage planes, colourless streak, vitreous lustre.
Found in aluminium-rich metamorphic pegmatites and sedimentary rock.
Used in refractory and ceramic products, electrical insulators, abrasives, gemstones.
Elongated, columnar crystals.
Anisotropic, i.e. two different harnesses on perpendicular axes.
12.2.6 Stilbite
Stilbite is a member of the zeolite group, lamellar zeolite, hydrated sodium calcium aluminium silicate, Ca(Al2Si7O18).6H2O.
Stilbite, hydrated sodium calcium aluminium silicate, has more than one chemical formula, e.g. Na2CaK2Al2Si7O18.7H2O, or
NaCa2Al5Si13O3614H2O, has white to pink to yellow colour, Mohs scale of hardness 3.5-4, white streak, glassy to pearly lustre,
good cleavage in one direction, specific gravity 4.56.
Note how thin crystals stick together like a sheaf of wheat, lustre and density of the specimen.
12.2.7 Zeolite
Zeolite (T5O10, T10O20 chains), e.g. tetrapropylammonium (TPA) ZSM-5, clinoptilolite
Zeolite, e.g. tetrapropylammonium (TPA)ZSM-5, is a group of natural or synthetic hydrated aluminium silicates, appear to boil when heated in a blowpipe.
They retain pores or channels in their crystal structure, easily gain or lose water, and have a high ion exchange capacity.
Zeolites are used in detergents as water softeners, and as catalysts for reforming petroleum products.
Sodium aluminosilicates, e.g. albite (NaAlSi3O8), jadeite (NaAlSi2O6), "Zeolite A", synthetic laundry detergent, Na12Al12Si12O48. 27H2O
12.3.1 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, then replace the stopper.
Hheat 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.
12.3.2 Aluminium chloride with water
12.3.2 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 hydrochloric acid + HCl gas.
Formation of an acid solution is more like a non-metal than a metal, which 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)
12.3.3 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.
12.3.4 Aluminium with acids
The reaction is very slow to start because ot the coating of aluminium oxide on aluminium.
After the acid has broken through the aluminium oxide, the reaction is fast, very fast if using powdered aluminium.
Dissolve aluminium in heated dilute hydrochloric acid and note that hydrogen gas forms.
2Al + 6H + --> 2A13+ + 3H2 (g).
2Al + 3H2SO4 --> Al2(SO4)3 + 3H2 Hot concentrated sulfuric acid will attack aluminium with the production of sulfur dioxide.
Dilute or concentrated nitric acid acts only very slowly on aluminium, because of passivation.
12.3.5 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) + 2Al(OH)4-+ 3H2 (g)
The aluminium reacts 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+ + 2Al(OH)4-
It is sold as "drain cleaners", e.g. Drano, contains sodium hydroxide crystals and pieces of aluminium, which react when put in a wet clogged drain.
The reaction is very hot as the sodium hydroxide reacts with fats to form soaps.
The hydrogen evolved 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 with more caustic soda and aluminium foil.
If the balloon does not float up in the air and feels heavy, the reaction has been too vigorous so some water has condensed in the balloon.
So wait until the bottle has cooled and repeat the experiment with>less caustic soda and aluminium foil.
12.3.6 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)
12.3.7 Bauxite digestion
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 oC to 1, 200 oC.
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.
12.3.8 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.
The 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.
12.3.11 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.
12.3.12 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.
2. Test aluminium
Test aluminium after dipping it in concentrated hydrochloric acid then press it on absorbent paper to remove the layer of aluminium oxide.
The voltage reading will start at a low value then increase as remaining aluminium oxide dissolves.
Record the maximum value.
12.3.13 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.
12.3.14 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.
12.4.0 Aluminium powder
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.
15.1.6 Corrosion of aluminium
Put a piece of aluminium foil in water. Put a copper coin on the foil and leave it for some days. A simple aluminium /copper cell forms and a small electric current can be detected with an ammeter. The aluminium foil has holes where the coin lies on it. The water appears cloudy, because of the fine particles of aluminium released during corrosion.