Page 97 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

Have you ever thought of the reason behind this? Let us do
some experiments.
Reaction with air

Cut a small piece of sodium with a knife. Observe the
metallic lustre at the newly formed surface. Keep it
exposed to air for some time.
Alloys
• What happened to the surface? What could be the
An alloy is a solid solution which is reason?
a homogeneous mixture of two or
more metals. Compared to metals, • Take an aluminium wire and rub its surface with
alloys possess better strength and
sand paper. Don’t you see a bright metallic lustre?
resistance to corrosion. More than
Within a few days, it gets tarnished. Why does it
90 percent of metals are used in
happen?
the form of their alloys. Alloys
represent a large class of
construction materials with
• Metals like copper, magnesium etc., also react
superior properties. An alloy of gold
similarly with atmospheric air.
and copper is used for making
ornaments. The components of When metals come into contact with atmosphere, they
some alloys are given below. undergo chemical reaction with different components
of air. As a result, the metal loses its lustre and gets
tarnished.
Alloy Components
Reaction of metals with water
Brass Copper, Zinc
Bronze Copper, Tin Take two beakers and fill three-fourth of them with
Nichrome Nickel, Chromium, water. Put a small piece of sodium in the first beaker
Iron and a piece of copper in the second. Write down your
Alnico Iron, Aluminium, observations.
Nickel, Cobalt
• Which of these metals reacted with water?
Small amounts of non metals
like carbon, silicon etc., are
also added to certain alloys • Which gas was formed during this reaction?
(eg. stainless steel).
Under favourable conditions, certain metals react with
water to form hydrogen gas.

Write down the chemical equation for the reaction
between sodium and water.

See 'Lohangal Sodium + Water Sodium hydroxide + Hydrogen
nashikkunnathu Thadayan' 2 Na + 2 H O 2 NaOH + H
in School Resources in 2 2
IT@School Edubuntu The metals potassium and calcium also react with cold
water.
96 Basic Science VIII