Chapter 6
description
Transcript of Chapter 6
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 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.
2
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)
3
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
This document was created with Win2PDF available at http://www.win2pdf.com.The unregistered version of Win2PDF is for evaluation or non-commercial use only.This page will not be added after purchasing Win2PDF.