7. Metals and Nonmetals exercise question answer 8th general science
General science question answer for 8th class – 8th class science all question answer – Class 8 general science chapter 7 question answer – Class 8 question answer Metals and non-metals
Q.1. Complete the table
|
Property of metal |
Use in everyday life |
|
i.
Ductility |
Gold, Silver ornaments |
|
ii.
Malleability |
Aluminium sheets, galvanised sheet |
|
iii.
Conduction of heat |
Satinless steel
vessels, copper vessels, boilers. |
|
iv.
Conduction of electricity |
Copper wires |
|
v.
Sonority |
Brass articles |
Q.2. Identify the odd term
a. Gold, silver, iron, diamond
Ans:
Diamond (others are metals)
b. Ductility, brittelness, sonority, malleability
Ans:
Brittlness (other properties are metallic property)
c. Carbon, bromine, sulphur, phosphorus
Ans:
Bromine (others are solids.)
d. Brass, bronze, iron, steel
Ans:
Iron (others are alloys.)
Q.3. Write scientific reasons.
a. 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,
the stainless steel vessels in kitchen have copper coating on the bottom.
b. Copper and brass vessels are cleaned with lemon.
Ans:
1. Copper undergoes oxidation in air to form black copper oxide . Copper oxide reacts slowly with carbon dioxide in air and gains a green coat . 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.
c. 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
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Q.4. Answer the following.
a. 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 with noncorroding 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 .
b. 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.
c. What are the adverse effects of corrosion?
Ans:
A
reddish coloured deposit ( rust ) is formed on iron by reaction with oxygen gas.
A
greenish coloured deposit (copper carbonate) is formed on copper by reaction
with carbon dioxide .
A blackish coloured deposit is formed ( silver
sulphide ) on silver .
Corrosion
causes damages to car bodies , bridges , iron railings , ships specially those
of iron , silver articles and copper vessels .
d. What are 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 .
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Q.5. Three experiments to study the process of rusting are given below. Observe the three test tubes and answer the following questions.
a. 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 .
b. 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 .
c. 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 .
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