Thursday, November 27, 2008

Making metals useful-gcse chemistry

Making metals useful

The reactivity of aluminium and anodisingAluminium is high in the reactivity series but does not corrode in air or water.

The reason is that aluminium covers itself with a thin layer of aluminium oxide which protects it from further corrosion.

Anodising is the industrial process of coating aluminium objects with a thicker layer of aluminium oxide.

The aluminium object forms the anode (positive electrode) in a sulfuric acid electrolyte during electrolysis.

Oxygen atoms form at the anode and join with the aluminium. This is oxidation.

Draw a labelled diagram for apparatus suitable for anodising an aluminium rod.

Show the electrodes, the electrolyte, and the cell.

Explain duralumin use in aircraft instead of aluminium.

Explain magnalium use in window frames instead of aluminium.

Important uses of aluminium and its alloys
metal or alloy

aluminium -overhead power cables

good electrical conductor, low density

aluminium -drinks cans -Does not react with water

aluminium -cooking pots -good heat conductor

duralumin -aircraft and bicycle parts -high strength, low density and hard

magnalium -aircraft parts -high strength, low density and corrosionresistance

Chemical reactions in different parts of the blast furnace (high tier)Iron is made in the blast furnace.

Write equations for each of the reactions in the blast furnace.

The limited uses of pure iron and impure iron from the blast furnaceImpure iron from the blast furnace (only 93% pure) is called cast iron.

Pure or wrought iron is not now mass produced but is still available.

cast iron

brittle, high compression strength
car engine blocks, man hole covers, gas stoves.

wrought iron
soft, bends easily, easily worked, low corrosion
nails, bolts, chains, garden gates, decorative ironwork

The production of mild steelIron from the blast furnace contains impurities like carbon, sulfur, silicon and phosphorus.

These are removed in the basic oxygen process. In this process a water cooled lance is put into impure molten iron and pure oxygen is blown through it.

The impurities are changed to oxides which come out as gases such carbon dioxide, and sulfur dioxide.

Solid oxides formed react with added calcium oxide to form a slag which floats on top of the iron.

When the amount of carbon drops to about 1 or 2% the process is stopped and the result is called mild steel.

The uses of mild steelMild steel containing a small amount of carbon eg 0.5% is has the hardness and strength for making machines, rails, ship's plates and girders for bridges and buildings.

The uses of alloy steelsThe properties of steels can be controlled by carefully changing the amounts of carbon removed and amounts of other metals put into them.

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chemistry notes / igcse-gcse- Olevel