8/6/2019 Group 13 Aluminium
1/48
AluminiumSymbol : Al
Proton number : 13
Electronic configuration : 2.8.3
Melting point : 660 oC
Boiling point : 2450 oC
Density : 2.70 g cm-3
Standard electrode potential : -1.66 VElectronegativity : 1.5
Lattice structure : Hexagonal close-pack
8/6/2019 Group 13 Aluminium
2/48
Most abundant metal on earth
3rd most abundant element on earth
Makes up about 8% of the Earths crust Very reactive element, hence does not occur naturally in the
uncombined state
Ores containing aluminium:
Bauxite Al2O3.2H2OGibbsite Al(OH)3
Diaspore AlO(OH)
Corundum Al2O3
Cryolite Na3AlF6
Kaolinite Al2Si2O7.2H2O
Feldspar KAlSi3O8
8/6/2019 Group 13 Aluminium
3/48
Extraction of
A l u m I n I u m
8/6/2019 Group 13 Aluminium
4/48
Purification of Bauxite
8/6/2019 Group 13 Aluminium
5/48
8/6/2019 Group 13 Aluminium
6/48
Electrolysis of Bauxite
8/6/2019 Group 13 Aluminium
7/48
Use this
a molten mixture of
cryolite (sodium
hexafluoroaluminate)with calcium and
aluminium fluoride
Melting point of aluminium oxide: 2050 oC
Melting point of aluminium oxide + molten cryolite: 900 oC - 950 oC
LOWER THE MELTING POINT OF ALUMINIUM OXIDE!
8/6/2019 Group 13 Aluminium
8/48
Hall-Heroult Process
8/6/2019 Group 13 Aluminium
9/48
At the anode (graphite):
Oxide ions are discharged
~ forms oxygen gas~ oxygen liberated reacts with carbon electrode
~ produces carbon dioxide and carbon monoxide
~ anode is corroded slowly and must be replaced from time to time
At the cathode (graphite):
Al3+ is reduced to liquid aluminium
~ melting point = 660 oC
~ denser than the electrolyte and sinks to the bottom of the cell~ drains off into moulds to cool
The overall chemical reaction is:
8/6/2019 Group 13 Aluminium
10/48
Note:Very high current (about 40,000 A) is used to maintain the temperature of the
electrolyte at 900 oC to prevent it from freezing
Low voltage (about 4.0 V) is used to prevent the fluoride ions from being
discharged. Fluorine and fluorine containing compounds are poisonous
8/6/2019 Group 13 Aluminium
11/48
8/6/2019 Group 13 Aluminium
12/48
8/6/2019 Group 13 Aluminium
13/48
8/6/2019 Group 13 Aluminium
14/48
Aluminium chloride: White solid at room conditions
Sublimes at 180 C
Soluble in water and organic solvents
Fumes in moist air
Covalent compound
8/6/2019 Group 13 Aluminium
15/48
Exist as a dimer at room conditions.
When heated. It will sublime as the dimer.
Dimer starts to disso
ciate at >400
Cto
AlC
l3 (g)
Complete dissociation at 800 C. *No MORE DIMER!!!!*
8/6/2019 Group 13 Aluminium
16/48
Undergoes hydrolysis in water.
Produces acidic solution
Al2Cl6 + 6H20 2Al(OH)3 + 6HCl
Anhydrous aluminium chloride is a catalyst.
WHEN??????
Benzene ring electrophilic substitution.
8/6/2019 Group 13 Aluminium
17/48
PREPARATIONOF ALUMINIUM CHLORIDE
Dry chlorine gas/ HCl gas pass over heated
aluminium powder.
2Al(s) +3Cl2(g) Al2Cl6(s) (white solid when cool)
8/6/2019 Group 13 Aluminium
18/48
Al ion has HIGHCHARGE DENSITYand empty orbitalsof valence shells.
Thus it can form complexes by receiving lone pair
from ligands.
8/6/2019 Group 13 Aluminium
19/48
FACTS on ALUMINIUM!!!
Most abundant metal on the earths surface
Light
Resistant to corrosion
100% recyclable and recycling process uses very little energy
One of the most difficult metal to extract, despite its
abundance
8/6/2019 Group 13 Aluminium
20/48
Used in:
High tension cables high electrical conductivity. Light.
Firefighter suits good thermal insulator. (Reflect heat)
DID you know???
Doctors wrap premature babies in foil to keep baby warm and
prevent heat loss from body.
Used in extractionofCHROMIUM and MANGANESE
(Thermite process) aluminium has high affinity for oxygen.
Alum K2SO4.Al2(SO4)3.24H2O. Cleans water.
Precipitates suspended particles.
8/6/2019 Group 13 Aluminium
21/48
Make CERAMICS: hard and stable even at high temperature
Cans// ThinSheets// Wires: very malleable and ductile
8/6/2019 Group 13 Aluminium
22/48
ANODISATION
Aluminium is a REACTIVEMETAL (based on E.C.S)
- It will react actively with O2 and dilute acid
- This will then form an OXIDE layer on metal surface
ANODE: 4OH- 2H20 +O2+ 4e
Oxygen liberated oxidises aluminium to aluminium oxides.
8/6/2019 Group 13 Aluminium
23/48
Function of anodisation:
- Used in industries. To FURTHERTHICKENthe aluminium
- Protects aluminium from further attack
- Also trap dyes: colourful!!! due to oxide layer. Waterproof.
8/6/2019 Group 13 Aluminium
24/48
Chemical
Properties of
Aluminum
8/6/2019 Group 13 Aluminium
25/48
Aluminum is a strong reducing agent and a
reactive metal
proof .^
~ large ve value in the standard electrodepotential (-1.66V)
The electron configuration
aluminum is 1s22s22p63s23p.
The outer three electrons occupy three s2p hybrid orbital that point in orthogonal
directions.
These electrons easily form covalent bonds, as in anhydrous AlCl3.
8/6/2019 Group 13 Aluminium
26/48
Reaction with non-metallic elements
Aluminum reacts directly when heated!
e.g. 4Al(s)+ 3O2(g)>>>>>2Al2O3(s)
2Al(s)+3S(s)>>>>>>>Al2S3(s)
2Al(s)+N2(g)>>>>>>>2AlN(s)
4Al(s)+3C(s)>>>>>>>Al4C3(s)
2Al(s)+3Cl2(s)>>>>>>Al2Cl6(s)
8/6/2019 Group 13 Aluminium
27/48
8/6/2019 Group 13 Aluminium
28/48
Reaction with sulphuric acid
Aluminium reacts with hot, dilute/concentrated sulphuric (VI) acid, liberating sulphur
dioxide gas
Reaction with dilute sulphuric acid is slow.
2Al(s)+6H2SO4(aq)>>>>>>Al2(SO4)3(aq)+ 3SO4(g)= 6H2O(l)
8/6/2019 Group 13 Aluminium
29/48
Reaction of aluminium with air
Aluminium is a silvery white metal.
The surface of aluminium metal is covered with a thin layer of oxide thathelps protect the metal from attack by air.
If the oxide layer is damaged, the aluminium metal is exposed to attack.
Aluminium will burn in oxygen with a brilliant white flame to form thetrioxide alumnium(III) oxide, Al2O3.
4Al(s)+ 3O2(l) 2Al2O3(s)
Same goes to water.
8/6/2019 Group 13 Aluminium
30/48
Reaction of aluminium with the halogens
Aluminium metal reacts vigorously with all the halogens to form aluminium halides.
It reacts with chlorine,Cl2 forming aluminium(III) chloride, AlCl3,
2Al(s)+ 3Cl2(l) 2AlCl3(s)
It reacts with Bromine,Br2 forming aluminium(III) bromide, AlBr3
2Al(s)+ 3Br2(l) 2AlBr3(s)
It reacts with iodine, I2, forming aluminium(III) iodide, AlI3.2Al(s)+ 3l2(l) 2All3(s)
8/6/2019 Group 13 Aluminium
31/48
Reaction of aluminium with bases
Aluminium dissolves in sodium hydroxide with the evolution of hydrogen gas, H2, and
the formation of aluminates of the type [Al(OH)4]-.
2Al(s)+ 2NaOH(aq)+ 6H2O 2Na+(aq)+ 2[Al(OH)4]- + 3H2(g)
8/6/2019 Group 13 Aluminium
32/48
Bonding inAluminum
compounds
8/6/2019 Group 13 Aluminium
33/48
Generally, aluminum forms ionic compounds with
covalent character.
reason: Al3+ ions have a higher charge density which
can distort the electron cloud of the neighboring
anion.
degree of covalent character
Polarising effect Polarisibility of anion of cationelectron cloud
Cation highly anion is large
charged has stronger and highly chargedPolarizing effect
easily polarized
8/6/2019 Group 13 Aluminium
34/48
For halide ions, polarisibility of an electron cloud
increases
Tendency to form covalent compound increases in
the following
F-
8/6/2019 Group 13 Aluminium
35/48
Gen
erally, to determin
e the bon
d formed is ion
ic,covalent or polarlised, consider the elements
electronegativity
Difference of electronegativity, @E between the
bonded elements is
a)@E=0, the bond is covalent bond
b)0
8/6/2019 Group 13 Aluminium
36/48
Aluminum oxide Al2O3
Aluminum oxide is a white solid with high
melting point of 2050C
INDICATION!
-Indicates bonding betweenAl3+ and O2- ions are
very strong
-lattice energy ofAl2O3
-is very high due to high charge and very small ionic
radius.
-RESULT!
-Al2O3 is insoluble in water
-Al2O3 has high melting point.
Corundum from crystalline Al2O3
8/6/2019 Group 13 Aluminium
37/48
Aluminum oxide Al2O3
Covalent character in ionic bond causes aluminum
oxide to be amphoteric
Aluminium oxide forms salt with acid and alkalis
Al2O3(s)+ 6HCl (l) 2ALCl3(aq)+3H2O(l)
Al2O3(s)+2NaOH(aq)+3H2O 2NaAl(OH)4(aq)
Corundum from crystalline Al2O
3
8/6/2019 Group 13 Aluminium
38/48
Aluminum oxide Al2O3
Uses ofAl2O3
a) Dehydration of alcohols to alkene
CH3CH2OH(l) C2H4(g)+H2O
Ethanol Ethene
b)Cracking of alkanes in petroleum industry
C6H14 C2H4(g)+C4H10(l)Hexane Ethene Butane
c)Refractory lining in the furnace
d)A
s an
adsorbin
g agen
t in
column
chromatography
Corundum from crystalline Al2O
3
350C
8/6/2019 Group 13 Aluminium
39/48
Aluminum Hydroxide Al(OH)3
Aluminum hydroxide is a white solid
- Prepared by adding excess aqueous ammonia tosolution containing Al3+ ions
NH3+H20 NH4++OH-
Al3++3H2O Al(OH)3
8/6/2019 Group 13 Aluminium
40/48
Aluminum Hydroxide Al(OH)3
Aluminum oxide is amphoteric
- It dissolves in both acid and alkalis
Al(OH)3(s)+ 3H+(aq) NH4++OH-
Al3++ 3OH Al(OH)4-
8/6/2019 Group 13 Aluminium
41/48
Aluminum Hydroxide Al(OH)3
IfCO2 is passed through the aluminate solution, Al(OH)3
is reprecipitated
Prove: aluminum hydroxide is a weak acid
2Al(OH)4-(aq)+CO2(g) 2Al(OH)3(s)+CO3(aq)+H2O(l)
8/6/2019 Group 13 Aluminium
42/48
Aluminum Hydroxide Al(OH)3
application of aluminum hydroxide
Used as a morda
nt in
dyein
g in
dustry to help dye biteup the fabric
Making water-proof clothing
8/6/2019 Group 13 Aluminium
43/48
Question time!
Remember!You get 1 mark for each
c
orrec
t answer!
8/6/2019 Group 13 Aluminium
44/48
1. What is the function of anodisation?
- Forms oxide layer to protect the aluminium
from further attack
- Traps dyes (waterproof)
- Increase thickness of aluminium
8/6/2019 Group 13 Aluminium
45/48
2. What form is aluminium chloride at room
temperature?
- Solid form. It is a white solid.
8/6/2019 Group 13 Aluminium
46/48
Aluminium is resistant to corrosion because
A) The presence of impervious oxide layer on the surface of
aluminiumB) Aluminium oxide is porous
C) The ionisation energy of aluminium is very high
D) Aluminium is less reactive
Answer:
A)
Corrosion is the oxidation of a metal by moisture and air. The presenceof non-porous oxide layer on the surface of aluminium shields the
aluminium from attack by moisture and air.
8/6/2019 Group 13 Aluminium
47/48
In the extraction of aluminium from bauxite, a current of 40000 A is used.
The function of the high current is to
A) Prevent the discharge of sodium ions from the dissociation ofcryolite
B) Increase the yield of aluminium
C) Keep the temperature of the electrolysis cell at 900 oC
D) Increase the rate of electrolysis
Answer:
C)
At temperature lower than 900o
C, the electrolyte will freeze. The highcurrent is necessary to generate heat to keep the temperature of the
electrolyte at 900 oC
8/6/2019 Group 13 Aluminium
48/48
Thank you!