Topic 11 - SABIS Grade 10 (Level M) Chemistry [Metals]

 Reactivity series:Metals are arranged in a decreasing order of their reactivity (in decreasing order of the tendency of a metal to
form its positive ion.)
The more reactive a metal is, the easier it is to form compounds and the harder it is to breakdown its
compounds

 Physical properties of alkali metals (Group 1 metals)

1. Soft metals, easily cut with a knife
2. Have low density.
3. Have shiny lustrous surface when freshly cut, but quickly tarnish when exposed to air.
4. Have low melting and boiling points compared to other metals, which decrease down the group.

2) Extraction of Calcium or Magnesium

(3) Extraction of Aluminium
Aluminium makes up 7.5% by mass of the Earth’s crust making it the most abundant metal in the Earth.
Its high reactivity is masked by a thin oxide layer that coats the metal. Aluminium spontaneously reacts with oxygen of the air to produce aluminium oxide which strongly adheres to the surface of the metal.

Ore: Bauxite: composed of aluminium oxide, water, iron (III) oxide and other impurities. The purified dry ore, called alumina, is aluminium oxide.

Requirements of extraction of Aluminium:

1. Source of electricity: preferably hydroelectric power.
   The process uses a great deal of electricity and is not cost-efficient unless the electricity is cheap.
2. Large supply of cooling water.
3. Raw materials (Bauxite and cryolite)
4. Good transport system
5. waste gases purification (to get rid of carbon monoxide, CO, and carbon dioxide, CO2 produced at the anode).

Often asked question:

Q: Anodes burn away and have to be replaced from time to time. Explain.A: Oxygen is produced at the anode and it reacts with it producing CO2 and CO, so the anode has to be replaced periodically.

 Uses of AluminiumUse                                                             Property

 

In cooking utensils In food containers	Resists corrosion (due to the protective oxide layer) Low density Good conductor of heat
Aircrafts (airplanes)	Low density High tensile strength (withstands high pressure) Resists corrosion (due to the protective oxide layer).
Steel cored aluminium cable steel core or Overhead power cables	Aluminium is used because it: is a good conductor of electricity has low density (less dense than copper that was previously used) Steel is used because it: expands less than copper has a high melting point. The steel is used to support aluminium which is a very good conductor.

Extraction of zinc

There are two methods of extraction:

Reduction Method Electrolysis method (80% of Zn is produced by this method)

  

 Steps: The ore ZnS is roasted in air. ZnS is oxidized (gains oxygen) 2 ZnS(s) + 3 O2 (g) → 2 ZnO(s) + 2 SO2 (g) Zinc oxide is reduced by coke or carbon monoxide (that act as a reducing agent) to zinc metal ZnO(s) + C(s) → Zn(g) + CO(g) ZnO(s) + CO(g) → Zn(g) + CO2(g) Zinc vapour and CO (or CO2) pass out of the furnace where zinc is cooled and condensed (Zinc is separated by fractional distillation)

 Steps: The ore ZnS is roasted in air. ZnS is oxidized 2 ZnS(s) + 3 O2(g) → 2ZnO(s) + 2SO2 (g) ZnO is dissolved in dilute sulphuric acid to form aqueous zinc sulphate.ZnO(s) + H2SO4 (aq) → ZnSO4 (aq) + H2O(l) Zinc sulphate solution is electrolysed using: (a) Carbon anode Oxygen evolves at the anode 4 OH-(aq) → 2 H2O(l) + O2 (g) + 4 e- or 2 H2O(l) → O2 (g) + 4 H+(aq) + 4 e- (b) Lead cathode Zn is collected at the cathode Zn2+(aq) + 2 e- → Zn(s)

uses of Zinc

Uses of Zinc:

1. Making alloys such as brass ( an alloy of Cu and Zn)
2. Galvanization
3. Car batteries
4. Sacrificial protection
   
   
   
   
   Aqueous copper (II) sulphate
   
   
   Steps: Impure copper is made the anode (connected to the positive terminal of the battery). Pure copper rod is made the cathode (connected to the negative terminal of the battery).  Electrolyte: Copper (II) sulphate solution (blue in color)

 Reactions and observations:At anode: Cu(s) → Cu2+(aq) + 2 e- Mass of the anode decreases due to the discharge of Cu metal At cathode: Cu2+(aq) + 2 e- → Cu(s) Mass of cathode increases.
Color of the solution stays blue (due to the continuous presence of copper (II) ions).Anode sludge that is formed below the anode contains solid impurities and can be removed by filtration.

(6) Extraction of Iron(a) Blast Furnace
Ore: Haematite (Iron (III) oxide Fe2O3) or Magnetite (Fe3O4)

 

Method: Reduction of the iron ore by carbon or carbon monoxide in the blast furnace.
Raw Materials: 1. Iron Ore (Fe2O3 or Fe3O4) 2. Coke, C 3. Limestone, CaCO3 4. Air