7. Metals and Non metals
1. Complete the table
|
Property of metal |
Use in everyday life |
|
i. Ductility ii. Malleability iii. Conduction of heat iv. Conduction of
electricity v. Sonority |
In electrical wires,
cable wires etc. Aluminium foil Cooking wares,
microwave, electric press, straightening machine, electric belts ulb, tubelight, lamp,
refrigerator, television Cymbals, doorbells |
2. Identify the odd term
a.
Gold, silver, iron, diamond
Ans: .Iron
is odd one out because iron is non-lustrous in nature and others are lustrous.
b. Ductility, brittelness, sonority,
malleability
Ans: Brittleness
is odd one out because it is a property of non-metals and rest are the
properties of metal
c. Carbon, bromine, sulphur, phosphorus
Ans: Bromine
is odd one out because it is liquid non-metal and others are solid non-metals.
d. Brass, bronze, iron, steel
Ans: Iron is
odd one out because it is not an alloy and others are alloys.
Class 8 chapter 7. Metals and Non metals maharashtra state board Text bool solution
3. Write scientific reasons.
a. The stainless steel vessels in
kitchen have copper coating on the bottom.
Ans: The
stainless steel vessels in Kitchen have copper coating on the bottom because
copper is good conductor of heat and electricity, by using copper
cookware, any meal can be prepared in a perfect and gentle way. They are the
best pots and pans for cooking
and roasting. This is particularly due to the fact that copper has excellent
material properties and is is cheap metal as compare to other metals.
b. Copper and brass vessels are
cleaned with lemon.
Ans: Copper
vessels get tarnished due to corrosion of copper metal. It forms a layer of
copper oxide, which is basic in nature. When lemon juice which contains citric
acid is added to it, neutralisation reaction takes place thus the vessel gets
cleaned.
c. Sodium metal is kept in kerosene.
Ans: Sodium
metal is kept in kerosene because sodium is very reactive metal. It is kept
in kerosene to prevent it from coming in contact with oxygen and
moisture. If this happens, it will react with the moisture present in air and
form Sodium hydroxide. This is a strongly exothermic reaction, and lot of heat
is generated. It will result out in the form of fire.
4. Answer the
following.
a. What is done to prevent corrosion of
metals?
Ans: We
can prevent corrosion by selecting the following things:
1. metal
type
2. protective
coating
3. environmental
measures
4. sacrificial
coatings
5. design
modification
b. What are the metals that make the alloys
brass and bronze?
Ans: Brass:
It is an alloy, that contains copper and zinc as major constituents.
Bronze: It is an alloy, that contains copper and tin as major constituents.
c. What are the adverse effects of corrosion?
Ans: The adverse effects of corrosion are as follows:
- Damage to commercial airplanes that could result in possible
in-flight problems
- Damage to oil pipelines that could cause a costly and dangerous
rupture that creates significant environmental damage.
- Damage to bridge supports that could cause a bridge failure
- Release of harmful pollutants from iron corrosion that contaminates
the air
- Contamination of product
- Damage of metallic equipments
- Inability to use metallic materials
- Lose of valuable materials such as blockage of pipes, mechanical
damage of underground water pipes
- Accidents due to mechanical lose of metallic cars, aircrafts etc.
- Causes pollution due to escaping products from corrosion
- Depletion of natural resource
- d.
What are uses of Noble metals?
Ans: Gold is bright yellow and a highly malleable and
ductile metal.
- Gold is used as the index of wealth. The countries which have more
gold reserve are considered to be wealthy.
- It is used for making ornaments.
- It is used for making high-value coins and medals.
- It is used for covering the mainframe of artificial satellites.
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: The
nail in the test tube 2 is not rusted because in test tube 2, we take boiling
water. So, all the dissolved oxygen is removed from water and if the iron nail
donot get supply of oxygen then corrosion is not carried out.
b. Why is the nail in the test tube 1
is rusted highly?
Ans: The
nail in the test tube 1 is rusted highly because in the test tube 1, iron nail
meets with all the requirements which is essential for the process of
corrosion. That's Supply of oxygen in dissolved form, presence of water and
material itself.
c. Would the nail in the test tube 3
get rusted ?
Ans: The
nail in the test tube 3 is not rusted because calcium chloride is one of the
best absorbent. So, it absorbs all the dissoved oxygen present in water. Hence
corrosion process is not take place.\