BY:

Cher Thu Yuen

Kenneth Chin

Jacqueline Teyew Ywan

Xing

Fong Chui Yeng

Jane Lee

2.1 The Extraction Of Aluminium

Purification Of The OxideBauxite

(Impure Al2O3)

Filter off Fe2O3 andother insoluble matter

H2O or CO2 added

Add NaOH (aq)

Filtrate contains Al(OH)4- and SiO3

2-

Filter to obtain Al(OH)3

Al(OH)3 decomposed by heat

Pure Al2O3

Al(OH)3 precipitate

Al(OH)3 Solid

The Electrolysis Of Aluminium Oxide

2.2 Bonding and Properties Of Aluminium Oxide and Chloride

Compounds

BONDINGIN ALUMINIUM

COVALENT

E.g.Aluminium Carbide Al4C3

Aluminium Nitride AlNAluminium Chloride Al2Cl4

IONIC WITH COVALENTCHARACTERISTICS

E.g.Aluminium Oxide Al2O3

Aluminium Hydroxide Al(OH)3

Why does aluminium forms Ionic Compounds with covalent characteristics?

Al3+ ions have high charge density which enablesit to polarise the electron cloud of and anion togive it a high degree of covalent character in theionic bond

Factors Affecting The Magnitude Of Covalent Characteristic In Ionic Bond

Factors Affecting The Magnitude Of Covalent Characteristic In Ionic Bond

Polarising Power of Cation:

Cations with ↓radii and ↑ charge have ↑ polarising power

Polarisability Of The Electron Cloud:

Anion with ↑ radii and ↑ charge are easily polarised

Ability of cation to polarise electron cloud of anion and tendency to form a covalent compound increases in the following order:

F<Cl<Br<I

Compound AlF3 AL2O3 Al2Cl6 Al4C3

% Covalent Character 20 30 60 70

What is it??

-- A white solid with very high melting point, 2050 0C(Due to bond between Al3+ ion and O2- ion is very strong

-- The ionic bond between 2 ions also showns significant covalent characteristics making Al2O3

amphoteric.

-- High Lattice Energy, therefore Al2O3 insoluble in water but dissolves in both hot acid & alkali

Acid: Al2O3 (s) + 6HCl (aq) → 2AlCl3 (aq) + 3 H2O (l)Alkali: Al2O3 (s) + 2NaOH (aq) → 2NaAl(OH)4 (aq)

USES OF Al2O3

USES OF Al2O3

Cracking

Dehydration

Cement

Refractory Furnance Bricks

Alcohol

Column Chromatography

Thin Layer Chromatography

As Stationary Phase

Set quickly

Resistant to sea water

THERMITE PROCESS

- A Redox Reaction

- Thermite = mixture of Al Powder + Fe2O3

When Ignited,

- A violent reaction occur

- Highly exothermic

- Al → oxidised

- Fe2O3 → reduced to white hot molten iron (sink to the bottom of the reaction mixture)

Uses:

- Welding Steel Object

- Making Bombs

- A white solid

- Types of bonding: Covelent + Van Der Waals Force of Attraction

-This causes AlCl3 to,

a) Sublines at low temperature

b) Dissolves easily in organic solvents

c) Form fumes in moist air

Passing dry chlorine / dry hydrogen chloride gas over aluminium powder

Al (s) + 3Cl2 (g) → Al2Cl6 (s)2Al (s) + 6HCl (g) → Al2Cl6 (s) + 3 H2 (g)

= All the apparatus used must be kept dry

= (Aluminium Chloride easily undergoes hydrolysis when exposed to moisture in air.

Al2Cl6 (s) + 6H2O (l) → 2Al(OH)3 (s) + 6HCl (g)

The solubility of AlCl3 is an extremely exothermic process.

Why?

-Hydration energy becomes more negative when the charge on the ions increases.

- Hydration energy becomes more negative when the size becomes smaller.

Al-Cl bond can be easily broken and this cause the standard electrode potential to be high for Aluminium.

AlCl3 (s) + 6H2O (l) → {Al(H2O)6}3+ (aq) + 3Cl- (aq) ; ∆H= -4610 KJ mol-1

Al (s) → Al3+ (aq) + 3e ; EΘ = - 1.66V

2.3 Acidic Character Of Aqueous Aluminium Salts

1. Soluble aluminium salts dissolve in water to produce Al3+ ions. e.g.

2. Aluminium salts forms the complex hexaaqualuminium (III) ions, {Al(H2O)6}3+, which has a octahedral geometry.

3. The high density charge of the central aluminium ion withdraws electron density from the O-H bonds in the water molecules thus weakening the bonds.

4. The hydrated complex ions is therefore likely to lose a proton, H+ and behave as an acid.

The Al3+ can act as a Bronsted-Lowry Acid. As a result, the aqueous solution of Al3+ ions are acidic.

Al2Cl6 (s) + aq → 2Al3+ (aq) + 6Cl- (aq)

{ Al(H2O)6}3+ (aq) + H2O (l) → {Al(H2O)5(OH)}2+ (aq) + H3O+ (aq)

5. In the presence of stronger bases, such as carbonate ion or the sulphide ions, the equilibrium above shifts to the right so that three protons are removed and hydrated aluminium hydroxide is precipitated with the release of carbon dioxide and hydrogen sulphide gas respectively.

• When sodium carbonate is added to aqueous aluminium salts, effervescence occurs.

• Other cations that give effervescence are Cr3+ (aq) and Fe3+ (aq)• Test for H2S: balckens lead (II) ethanoate paper

6. In excess of strong bases such as sodium hydroxide, NaOH, the aluminium hydroxide forms diaquatetrahydroxoal uminate (III) ions / aluminate.

Al(OH3) (s) + OH- (aq) → {Al(OH)4}- (aq)

2{Al(H2O)6}3+ (aq) + 3CO32- (aq) → 2Al(OH)3.3H2O (s) + 2CO2 (g) + 3H2O (l)

2{Al(H2O)6}3+ (aq) + 3S2- (aq) → 2Al(OH)3.3H2O (s) + 3H2S (g) + 3H2O (l)

H2S + (CH3COO)2Pb → PbS (s) + 2CH3COOH

2{Al(H2O)6}3+ (aq) + 3CO32- (aq) → 2Al(OH)3.3H2O (s) + 2CO2 (g) + 3H2O (l)

2{Al(H2O)6}3+ (aq) + 3S2- (aq) → 2Al(OH)3.3H2O (s) + 3H2S (g) + 3H2O (l)

7. In dilute acid added to aluminate, equilibrium shifts to the left and aluminate hydroxide is reprecipitated. If in excess acid, precipitate dissolves

8. The high charge density of Al3+ ion enables it to be used as coagulating agents for the coagulation of blood and organic materials in water.

Al(OH3) (s) + 3H+ (aq) → Al3+ (aq) + 3H2O (l)

2.4 Resistance Of Aluminium To Corrosion

1. Aluminium is a reactive metal, therefore it react very actively with oxygen and dilute acid

2. When aluminium exposed to air / reacted with dilute acid, a thin, non-porous oxide layer, Aluminium Oxide is form.

3. Oxide layer protect aluminium from further reaction.

4. In industry, protective oxide can be thickened using anodisation process

2.5 The Uses of Aluminium And Its Compounds In Industry

ALUMINIUMALUMINIUM

GOOD CONDUCTOR OF HEAT

GOOD CONDUCTOR OF HEAT

GOOD CONDUCTOR OF ELECTRIC

GOOD CONDUCTOR OF ELECTRIC

RESISTANT TO CORROSION

RESISTANT TO CORROSION

LIGHT IN WEIGHT

LIGHT IN WEIGHTSHINNY SURFACESHINNY SURFACE

ALLOY OF ALUMINIUM

Duralumin(95% Al; 4% Cu; 1% Mg, Fe, Si) Construction Materials

Magnalium (83% Al; 15% Mg; 2% Ca) Body of Aircrafts

ALUMINIUM AND ITS COMPOUND

Alums (MI2SO4.MII

2(SO4)3 . 24H2O) Used to clean water and sewage

Ceramics Making cement, tiles, water container,

window glass, etc.