7 – Metals and Non-Metals
Q 1.Identify
the odd term:
Ans
(1) Diamond.
(Others are metals.)
(2)
Brittleness. (Other properties metallic properties.)
(3)
Bromine. (Others are solids.)
(4) Iron. (Others are alloys.)
Q. 2
Give scientific reasons :
(1)
The stainless steel vessels in kitchen have copper coating on the bottom.
Ans.
(1) Stainless steel is an alloy of iron with carbon, chromium and nickel.
(2) The conductivity of copper is higher than that
of iron in steel. Copper heats uniformly and faster. The time for cooking is
reduced, as a result it saves fuel. Hence, we stainless steel vessels in
kitchen have copper coating on the bottom.
(2) Copper and brass vessels are cleaned with lemon.
Ans Copper underegoas oxidation in air to form
black copper oxide. Copper oxide reacts slowly with carbon diaoxide in air and
gains a green caot. This green substance is copper carbonate. (2) Lemon contains
acid. The acid dissolves the green coating of basic copper carbonate present on
the surface of a tarnished copper and brass vessels and makes them shiny again.
(3) Sodium metal is kept in kerosene.
Ans.
(1) Sodium reacts so vigorously with atmospheric oxygen and water that it
catches fire if kept in the open. (2) It does not react with kerosene and sinks
in it. Hence, to protect sodium and to prevent accidental fires it is always
kept in kerosene
Q 3.
Answer the following.
(1) What are the uses of noble metals?
Ans. Uses of Noble Metals:
(1)
Gold, silver and platinum are used to prepare ornaments.
(2)
Silver is used in medicines. (It has antibacterial property),
(3)
Gold and silver are also used to make metals and few electronic devices.
(4)
Platinum, palladium metals are used as catalyst.
(2)
What is done to prevent corrosion of metals?
Ans.
By applying a layer of paint, oil, grease or varnish on the surface of a metal
to prevent corrosion. Also plating 'Will non corroding metal is done. Iron is
coated with thin layer of zinc. Due to these processes the contact of metal
surface with air is lost and corrosion is prevented.
(3) What
are the adverse effects of corrosion?
Ans.
(1) A reddish coloured deposit (rust) is formed on iron by reaction with oxygen
gas.
(2) A greenish carbonate) is for (copper carbonate) is formed on
copper by reaction
with
carbon dioxide.
(3) A blackish
coloured deposit is formed (silver sulphide) on silver.
(4) Corrosion
causes damages to car bodies, bridges, iron railings, ships specially of iron,
silver articles and copper vessels.
(4)
What are the metals that make the alloys brass and bronze?
Ans.
The alloy brass is formed from copper and zinc and the alloy bronze is formed
from copper and tin.
.
Q. 4
Complete the table : (Answers are given directly.)
Property of metal Use in everyday life
(1)
Ductility (1) Gold, silver ornaments
(2)
Malleability (2)
Aluminium sheets, galvanised sheets
(3)
Conduction of heat (3) Stainless steel vessels,
copper vessels, boilers
(4)
Conduction of electricity (4)
Copper wires
(5)
Sonority (5) Brass
articles
Q.5. Activity-based question :
• Activity - Three experiments to study the process of
rusting are given below. Observe the three test tubes and answer the following
question
(1) Why the nail in
the test tube 2 is not rusted?
Ans. In the test tube 2, oil cuts the supply of air to nail
due to which oxidation of nail is prevented and boiled water is free from
gases. Hence, the nail in the test tube 2 is not rusted.
(2) Why is the nail in the test tube 1 is rusted highly?
Ans. The nail in the test tube 1 is highly rusted because
nail is in contact with water and air. The oxidation process is fast.
(3) Would the nail in the test tube 3 get rusted?
Ans. No change is observed in the test tube 3. Nail remains
as it is because the calcium chloride absorbs moisture, making the air dry,
thus preventing rusting of the nail.
