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1 Chapter 6 : Metal and nonmetal i) General comparison between metals and nonmetals • ii)Metal Aluminum Industrial production of aluminum Physical and chemical properties Applications Iii)Nonmetals Preparations of chlorine in laboratory (concentrated HCl) Industry ( electrolysis:Down’s method) Chemical test Physical and chemical properties Applications General comparison between metals and nonmetals METALS Form cation in aqueous Good heat and electrical conductor High melting and boiling point Usually appear as solid at room temperature Formed basic oxides NONMETALS Industrial production of Aluminum : Extraction of Aluminum using electrolytic method The ore containing aluminum compaund, which is comercially used in the extractive metallurgy is called bauxite. Bauxite is a hydrated aluminum oxide. Extraction of aluminum from bauxite is carried out in three stages: Ore dressingcleaning ore by means of separation of the metal containing mineral from the waste (gangue). Chemical treatment of bauxite for converting the hydrated aluminum oxide to pure aluminum oxide. Reduction of aluminum from aluminum oxide by the electrolytic process. Al 2 O 3 in molten cryolite Steel (Fe) Process of extraction of aluminum: Aluminium is obtained by the electrolytic reduction of its molten oxide, alumina (Al 2 O 3 ). Hall-Heroult process Alumina is a very poor electricity conductor and has a very high melting point (2045ºC). Therefore the mineral cryolite (Na 3 AlF 6 ) is added to lower the melting point. During the electrolysis of Al 2 O 3 , the pure aluminium is attracted to the cathode, At the cathode, reduction takes place : Al 3+ + 3e - Al Then the oxygen is attracted to the anode, At the anode, oxidation takes place : 2O 2- O 2 + 4e - However, at HIGH temperature of the cell, the carbon anodes burn in this oxygen to form carbon dioxide. Continual replacement of the anodes is a major expense.
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Page 1: Chapter 6

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Chapter 6 : Metal and nonmetal• i) General comparison between metals and

nonmetals

• ii)Metal– Aluminum

• Industrial production of aluminum• Physical and chemical properties• Applications

• Iii)Nonmetals– Preparations of chlorine in

• laboratory (concentrated HCl)• Industry ( electrolysis:Down’s method)• Chemical test• Physical and chemical properties• Applications

General comparison between metals and nonmetals

• METALS– Form cation in

aqueous– Good heat and

electrical conductor– High melting and

boiling point– Usually appear as

solid at room temperature

– Formed basic oxides

• NONMETALS

Industrial production of Aluminum : Extraction of Aluminum using electrolytic

method• The ore containing aluminum compaund, which is comercially used

in the extractive metallurgy is called bauxite.

• Bauxite is a hydrated aluminum oxide.

• Extraction of aluminum from bauxite is carried out in three stages:– Ore dressing– cleaning ore by means of separation of the metal

containing mineral from the waste (gangue).

– Chemical treatment of bauxite for converting the hydrated aluminum oxide to pure aluminum oxide.

– Reduction of aluminum from aluminum oxide by the electrolytic process.

Al2O3 in molten cryolite

Steel (Fe)

Process of extraction of aluminum:• Aluminium is obtained by the electrolytic reduction of its molten

oxide, alumina (Al2O3). Hall-Heroult process

• Alumina is a very poor electricity conductor and has a very high melting point (2045ºC). Therefore the mineral cryolite (Na3AlF6)is added to lower the melting point.

• During the electrolysis of Al2O3, the pure aluminium is attracted to the cathode, – At the cathode, reduction takes place :

Al 3+ + 3e- Al

• Then the oxygen is attracted to the anode, – At the anode, oxidation takes place :

2O2- O2 + 4e-

• However, at HIGH temperature of the cell, the carbon anodes burn in this oxygen to form carbon dioxide.

• Continual replacement of the anodes is a major expense.

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Some economic and environmental considerations

• Economic considerations• Think about:

– The high cost of the process because of the huge amounts of electricity it uses.

– Energy and material costs in constantly replacing the anodes

• Environmental problems in mining and transporting the bauxite

• Think about:– Loss of landscape due to

mining– Noise.– Atmospheric pollution from the

various stages of extraction. For example: carbon dioxide from the burning of the anodes (greenhouse effect);

Physical properties of aluminum:

• Aluminium is a soft, lightweight metal• has a low density • is a good electrical conductor• good heat conductor• has a good appearance• nontoxic/ nonpoisonous• nonmagnetic

Chemical Properties of Aluminum:

1) Resists corrosion because of the strong thin layer of oxide on its surface that helps protect the metal from attack by air. So, normally, aluminum metal does not react with air.

2) Aluminum will burn in oxygen to form the aluminum oxide, 4Al(s) + 3O2(l) 2Al2O3(s)

3) Aluminium metal reacts vigorously with all the halogen: 2Al(s) + 3Cl2(l) 2AlCl3(s)2Al(s) + 3Br2(l) Al2Br6(s)

4) Dissolve in acid and bases2Al(s) + 6HCl 2Al3+ + 6Cl- + 3H2(g)2Al(s) + 2NaOH + 6H2O 2Na+ + 2[Al(OH)4]- + 3H2(g)

5) Good reducing agent (easily oxidized), especially LiAlH4

Application of aluminum:

• for aircraft industry• useful for construction and automotive

industries• electrical conductor• useful for cookware

The Preparation of Chlorine in theLaboratory

Production of chlorine in industry:Down’s method

Na+ ions migrate to cathode where they are reduced to Na.

Cl--ions migrate to anode and oxidised to form chlorine gas

Na+ + e- Na (Reduction)

2Cl- Cl2 + 2e- (Oxidation)

Na+ + e- Na

__________________ 2Na+ + 2Cl- 2Na + Cl2

2Cl- Cl2 + 2e- (Oxidation)

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DRAW BACKS OF DOWN'S METHODMelting point of NaCl is 801C. At this temperature

molten NaCl and Na form a metallic fog in the container which is impossible to separate.

In order to over come this difficulty instead of only NaCl, a mixture of NaCl and CaCl2 is electrolyzed in down's cell. The melting point of this mixture is 600C. At 600C no metallic fog is formed.

Chemical test for chlorine

• Test for Chlorine Gas, Cl2(g).• 1) Is green-yellow in colour.• 2) Has a pungent choking smell.• 3) Will turn moist litmus or universal

indicator paper red, and then bleach it white.

Some of the chemical/physical properties of chlorine include:

• Some of the chemical/physical properties of chlorine include:• Chlorine is a yellow-green gas at room temperature. • Chlorine has a pungent, irritating odor• The density of chlorine gas is approximately 2.5 times greater than

air• Chlorine is not flammable, but may react explosively or form

explosive compounds • Chlorine is slightly water soluble• reacts with water to produce hypochlorite, OCl-. • slightly soluble in water • non-combustible gas at room temperature and at standard pressure.• Chlorine is highly reactive, especially with hydrogen.

Applications of chlorine

• Bleaching agent• Disinfectant• Raw material for production of chemicals

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