1. Group 3 Members General comment
Elements symbol
Boron B
Aluminium Al
Gallium Ga
Indium In
Thallium Tl
General comment
Boron is a nonmetal, aluminium is a metal whereas gallium, Indium and Thallium are weakly metallic.
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2. Group 3 Uses of boron Aluminium
1. Boron is used in making heat resistant glasses
2. Boron is a essential nutrient.
3. Sodium tetra borate (borax), Na2B4O7. 10H2O is used to standardize hydrochloric acid solutions.
Na2B4O7 (aq) + 2HCl (aq) + 5H2O (l)
→ 2NaCl (aq) + 4H3BO3 (s)
Aluminium
Aluminium is a light metal that strong, malleable and ductile.
Its surface is protected by a thin layer of oxides the prevents from being very reactive.
It is used for electric cables, sauce pans, tins, airplanes.
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3. Group 3 Extraction of Aluminium Principles in extraction
Ore: Bauxite (Al2O3.xH2O)
Major impurities are
Silica or SiO2
Iron salts
Principles in extraction
Extraction of aluminium involves removal of impurities (purification) and then reduction to metal by electrolysis.
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4. Group 3 Steps in extraction of Aluminium
The ore is heated
to remove water and,
To convert iron salts to iron III oxide
Steps in extraction of Aluminium
2. The powdered ore is heated with concentrated sodium hydroxide to dissolve aluminium oxide and silica such that the insoluble iron oxide is filtered off.
Aluminium oxide form aluminate
Al2O3 (s) + 2NaOH (aq) + 7H2O (l)
→ 2Na[Al(OH)4(H2O)2] (aq)
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5. Group 3 Steps in extraction of Aluminium Al2O3 (s) + OH-(aq)
Or the ionic form
Al2O3 (s) + OH-(aq)
→ 2AlO2-(aq) + H2O(l)
Silica also dissolves forming sodium silicate.
SiO2 (s) + 2NaOH (aq)
→ Na2SiO3(aq) + H2O (l)
Steps in extraction of Aluminium
3. To the filtrate A little aluminium hydroxide is added to precipitate Aluminium hydroxide,(seeding).
NaAlO2(aq) + 2H2O(l)
→ NaOH(aq) + Al(OH)3(s)
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6. Group 3 Steps in extraction of Aluminium
Alternatively carbon dioxide bubbled through the filtrate to precipitate aluminium hydroxide as follows
2NaAl(OH)4(aq) + CO2(g) →
2Al(OH)3(s) + Na2CO3(aq) + H2O(l)
Steps in extraction of Aluminium
4. The precipitated aluminium hydroxide is filtered off, washed and ignited to give pure aluminium oxide (alumina).
2Al(OH)3(s) → Al2O3(s) + 3H2O (g)
Alumina
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7. Group 3 Steps in extraction of Aluminium
5. Aluminum is obtained form aluminium oxide by electrolysis.
Cryolite, Na3AlF6, is added to
lower the melting point of alumina from20500C to 9000C
and improve conductivity of aluminium oxide
Steps in extraction of Aluminium
At the cathode (carbon) aluminium is liberated
Al3+ (aq) + 3e- → Al (s)
At the anode (carbon) oxygen is liberated
2O2- - 4e → O2 (g)
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8. Group 3 Steps in extraction of Aluminium
The anode is eaten up by oxygen
C + O2 (g) → CO2 (g)
Trial 1
During the extraction of aluminium, the ore is first purified.
(i) Write the name and formula of one ore from which aluminium is extracted. (1 marks)
(ii) Name two main impurities in the ore. (1 marks)
(iii) Name the reagent that is used in the purification of the ore (1 marks)
The purified ore is mixed with caryolite, melted and electrolyzed.
(i) State the purpose of adding caryolite. (1 mark)
(ii) Name the electrodes used. (1 mark)
(iii) Write an equation for the reaction that takes place at the cathode during the electrolysis. (2 marks)
Write an equation to show how anhydrous aluminium chloride can be obtained from aluminium. (2 marks)
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9. Group 3 Reactions of aluminium (a) with non metals
Trial 2
Write the formula of an ore of aluminium.
During the extraction of aluminium, the ore is first treated with sodium hydroxide, followed by aluminium hydroxide.
State the purpose of adding sodium hydroxide. (1.mark)
Write an equation for the reaction between the ore and sodium hydroxide. (1½ marks)
What is the purpose of adding aluminium hydroxide?
(1 mark)
Briefly explain how aluminium can be obtained after the ore has been treated as in (b).(3.marks)
Carbon dioxide was used instead of aluminum hydroxide in (b).
Write an equation for the reaction that took place.
Reactions of aluminium
(a) with non metals
Aluminium combines directly with oxygen, sulphur, nitrogen and halogens at appropriate conditions.
4Al (s) + 3O2 (g) → 2Al2O3(s)
4Al (s) + 6S (s) → 2Al2S3(s)
2Al (s) + N2 (g) → 2AlN (s)
2Al (s) + 3F2 (g) → 2AlF3(s)
The oxide and fluoride are ionic, and the rest are predominantly covalent.
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10. Group 3 Reactions of aluminium Reactions of aluminium
(b) Reaction with HCl
Aluminium reacts with moderately concentrated HCl to give a chloride and hydrogen gas.
2Al (s) + 6HCl (aq)
→ 2AlCl3(s) + 3H2(g)
Reactions of aluminium
(c) with sulphuric acid
Aluminum is not readily attacked by dilute sulphuric acid, but with the concentrated acid it gives the sulphate and sulphur dioxide and water.
2Al (s) + 4H2SO4(aq) →
Al2(SO4)3(s)+ 2H2O(l) + SO2(g) + 2H2(g) .
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11. Group 3 Reactions of aluminium Reactions of aluminium
(d) Reaction with nitric acid
Aluminium does not react with nitric acid probably due to formation of an impenetrable oxide layer on the surface.
Reactions of aluminium
(e) Reaction with sodium hydroxide
Aluminium reacts with sodium hydroxide liberating hydrogen gas.
 2Al(s) + 2-OH(aq) + 6H2O(l)
→ 2Al(OH)4-(aq) + 3H2(g) .
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12. Group 3 Halides of aluminium (a) Aluminium fluoride (AlF3)
It can be made by reacting metallic aluminium with fluorine. It is the only ionic aluminium halide and it is sparingly soluble in water.
Halides of aluminium
(b) Aluminium chloride, Al2Cl6
 Preparation:
1. By passing hydrogen chloride or chlorine over heated metal under anhydrous conditions.
2Al(s) + 3Cl2 (g) → Al2Cl6 (s)
2Al(s) + 6HCl (g)
→ Al2Cl6 (s) + 3H2 (g)
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13. Group 3 Halides of aluminium Covalent bond Halides of aluminium
(b) Aluminium chloride, Al2Cl6
 Preparation:
2. By passing chloride gas over a mixture of aluminium oxide and charcoal heated to about C.
Al2O3 (s) + 3C (s) + 3Cl2
→ Al2Cl6 (s) + 3CO (g)
Halides of aluminium
Structure of aluminium chloride
Covalent bond
Dative bond
Cl Cl Cl
Cl Cl Cl
Al Al
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14. Group 3 Oxide of aluminium Trial 3 Preparation
(a) The relative molecular mass of aluminium chloride in a vapour phase is 267.
(i) Write the molecular formula of aluminium chloride in a vapour phase.
(ii) Write a structural formula to show the bonding in aluminium chloride vapour.
(iii) Note the types of bonds involved in the structure you have drawn in (ii) above.
Oxide of aluminium
Preparation
By heating aluminium with oxygen or
by heating aluminium hydroxide
2Al(s) + 3O2  → 2Al2O3 (s)
2Al(OH)3(s) → Al2O3(s) + 3H2O(g)
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15. Group 3 Trial 4 Oxide of aluminium Reactions
1. Aluminium oxide is amphoteric, thus, reacts with both acids and alkalis to give salts.
 Al2O3(s) + 6H+ (aq)
→ 2Al3+ (aq) + 3H2O (l)
Al2O3(s) + 2-OH (aq) + 3H2O (l)
→ 2Al(OH)4- (aq)
Trial 4
With reference to aluminium oxide, explain the term amphoteric property.
Write appropriate equations
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16. Group 3 Hydrolysis of aluminium salts
Aluminium salts produce acidic solution because they hydrolyze in water to form hydrogen ions as follows:
Al3+(aq) + 3H2O (l)
→ Al(OH)3(s) + 3H+(aq)
Hydrolysis of aluminium salts
Due to hydrolysis
Aluminium salt solution turn blue litmus paper red.
Al3+ salt solutions are cloudy due to formation of insoluble Al(OH)3.
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17. Group 3 Hydrolysis of aluminium salts Due to hydrolysis
Aluminium salt solution give off a gas with a white precipitate of aluminium hydroxide when reacted with sodium carbonate solution.
2Al3+(aq) + 3CO32-(aq) + 3H2O(l)
→ 2Al(OH)3 (s) + 3CO2 (g)
Trial 5 Explain, giving the necessary equations, why, (i) solutions of simple Al3+ salts are acidic. (ii) aluminium utensils should not be washed in strong alkaline solution.
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18. Group 3
Trial 5
How and under what conditions does aluminium react with
(i) hydrochloric acid,
(ii) nitric acid
(iii) sodium hydroxide
(iv) iodine
(v) iron (III) oxide.
Trial 6
Aluminium metal is prepared by an electrolytic method and not by heating aluminium oxide with coke in a blast furnace.
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19. Group 3 Qualitative analysis of Al3+ With sodium hydroxide
It forms a white precipitate soluble in excess.
Al3+ (aq) + 3OH-(aq) → Al(OH)3(s)
Al(OH)3 (s)
OH- (excess) Al(OH)4- (aq)
Qualitative analysis of Al3+
With dilute ammonia
It forms a white precipitate.
Al3+(aq) + 3OH-(aq) → Al(OH)3(s)
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20. Group 3 End Qualitative analysis of Al3+
With sodium carbonate solution
It forms a white precipitate with effervescence, soluble in excess.
2Al3+ (aq) + 3CO32- (aq) + 3H2O (l)
→ 2Al(OH)3(s) + 3CO2(g)
Then
2Al(OH)3 (s) + CO32- (aq) + H2O (l)
→ 2Al(OH)4- (aq) + CO2(g)
End
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