Page 41 - Science Class 08
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Hardness also behave like that. Iron gets rusted with a
Metals are generally hard and difficult to cut. brownish layer of its oxide.
This hardness is their strength and they can Highly reac ve metals like sodium at once catch
bear heavy loads. That is why they are used to fire in air and form sodium oxide (Na O). That is
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make bridges, machines and buildings. why sodium is always kept in kerosene.
But, some metals do not hold these proper es. Ac on with Water
Gallium has a low mel ng point and it melts Metals react with water in various ways:
when placed on the hand-palm. Sodium
v Copper, silver and gold do not react with
and potassium are so so that they can be water at all.
easily cut.
v Iron and zinc react only mildly with steam,
Some more physical proper es of metals are: not with cold water.
v They reflect light due to their shine. v Magnesium reacts mildly with cold water
v They have high specific gravi es. but it reacts vigorously with steam to form
v They give out sound when struck, i.e., they magnesium hydroxide and hydrogen.
are sonorous. v Sodium also reacts with cold water to form
CHEMICAL PROPERTIES OF METALS sodium hydroxide and hydrogen.
Mg + 2H O Õ Mg (OH) + H
Reac on with Oxygen 2 2 2
2Na + 2H O Õ 2NaOH + H
Metals form oxides when they react with 2 2
oxygen. Reac on with Acids
Metals react with acids in different ways. Most
of them produce salts and hydrogen gas in their
reac ons.
Take a piece of magnesium ribbon. Hold it
with a pair of forceps and place it over a
flame. It will kindle with a bright white light
Collect some pieces of various metals– iron,
as also will be reduced to ash that is the
zinc, copper, aluminium and magnesium. Put
oxide of magnesium. It was formed when
magnesium combined with oxygen of the air. these pieces in separate test-tubes and add a
li le hydrochloric acid to each test-tube. If no
Put this ash into a li le water in a jar. It will ac on takes place, then heat the test-tube
dissolve only par ally. Test this solu on on mildly keeping your face away from the
red litmus paper. It will turn its colour to blue mouth of the test-tube.
showing thereby that magnesium oxide has a
basic (alkaline) nature. A gas will be given out as a result of the
reac on in each test-tube. Test this gas by
Ac on with Air bringing a glowing splinter near the mouth of
A freshly polished copper, when placed in the the test-tube. The gas will burn with a pop-
air, becomes dull in a short me, i.e. it loses its sound showing thereby that it is hydrogen.
lustre due to the ac on of oxygen of the air on But in the case of copper, there is no reac on.
it. The ac on leads to the forma on of copper As for magnesium, it reacts strongly with dilute
oxide which is dull looking. Iron and aluminium hydrochloric acid. Other metals will react with
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