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Friday, 14 September 2018

Identification of Metals



   Metals have characteristics which are different from those of non metals such as wood, plastics, ceramics, rubber, etc. Metals and non metals can be distinguished using the following properties of metals - Density, colour/lustre, fusibility, magnetic effect, conductivity of heat, sound test, etc.

Density 

The heaviness or lightness of a substance for a given volume is called density. If we take a cube of a substance with dimensions @ metre by 1 metre by 1 metre, its volume is 1 cubic metre. 1 cubic metre of steel weigh 8,000 kilograms. So we say steel has a density of 8,000kg / cubic metre. Water has a density of 1,000 kg/ cubic metre. Aluminum has a density of 2,800kg/ cubic metre. Thus , aluminum is lighter than steel but heavier than water of the same volume. Plastic are much lighter, with density varying from 900kg to 1,600kg per cubic metre.

Colour / lustre

This is the appearance of a material when the surface is polished. Different woods show different appearances when polished. The same thing applies to metals.

Fusibility

Metals can melted until they become liquid. This is important property of metals. Non metals do not have such property. They usually burn when heated to high temperature. Metals have different melting  points or temperature of cast iron is about 1,241°C while that of  wrought iron is  about 2,005°C.

Magnetic effect

When a magnet picks a material , the material is said to be magnetic. Non metals, e.g . wood, ceramics, plastics, etc.., are not magnetic. Thus you cannot use a magnet to pick a piece of wood. Also, not all metals are magnetic. Only metals that are magnetic. They are called ferrous metals. All the other  non magnetic metals are called non ferrous metals. By using magnets we can easily identify ferrous and non ferrous metals.

Conductivity of heat

Metals are better conductors of heat than non metals. Thus , in a heating kettle the metallic part of the handle is much hotter than the wooden part. Therefore, we hold the wooden part to lift the kettle from the fire.

Sound test

When metals are hit, the emit different sounds , for example, a bell made of brass and another one made of steel, will give different sounds when hit with a hammer. Different sounds are emitted from the different causes.

Experiments

Polishing for lustre effect

Students ate to cut out the following material for this experiment:

(a) Steel plate 5cm x 5cm x 2cm

b) Aluminium plate 5cm x 5cm x 2cm

c) Brass plate 5cm x 5cm x 2cm

Polish the surface of each of these metals using a fine emery cloth. After polishing , the light reflecting emery properties of these materials can be noticed and compared.

Density test

Cut samples of  different materials. They may have different dimensions; but make sure they have the same volume. For this experiment, you can use copper, iron, wood, aluminum. Weigh each sample , using simple scale. Record the weights and arrange the materials in increasing order of their weights. The higher the weight the greater the density of the material.

Heat condition test

If one end of material is heated , the other end soon becomes hot also. We say that the heat from the hot end gas been conducted along the bar towards the cold end. In general, metals are good conductors of heat, but some metals conduct heat better than others. Other materials such as wood, glass and paper are very poor heat conditions.

The arrangement is to test the rate of heat conduction of a bar of metal. Place a less solder or wax at the end of a bar  of copper. Heat the bar at one end and record the time it takes for the soldier or wax to start to melt. Repeat the experiment using other materials such as brass, aluminium and steel with the same diameter and length as the  cooper bar. Record in each case the time it takes to melt the lead solder or wax.
Using your result, arrange the materials from the best to the poorest heat conductors. 

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