6 –
substances in daily use
Q. 1. Fill in
the blanks using proper words:
(1) Rubber made by vulcanization is_______,
______ material.
(2) Man-made materials are made by ....... natural
materials.
(3).............. thread was developed simultaneously in New
York and London.
(4) Rayon is also known as _________.
Ans. (1) Rubber made by vulcanization is artificial, hard
material.
(2) Man-made materials are made by processing natural
materials.
(3) Nylon thread was developed simultaneously in New York and
London.
(4) Rayon is also known as synthetic silk.
Q 2 What are we
used for?
(1) Soil :
Ans. Soil is used for farming and agriculture. It is also
used in constructions bricks and clay tiles are made from soil. Pots, urns,
clay stoves etc made form soil.
(2) Wood :
Ans. Furniture is made from wood. The doors and windows of
houses are also made from wood. Therefore, in construction activities wood is
largely used. Wood also gives fuel many useful articles are also made from
wood.
(3) Nylon :
Ans. Nylon threads are durable and hence used making ropes,
fishing nets and
clothes.
[4) Paper :
Ans. Paper is for writing, for making books, notebooks,
registers. greeting cards. etc. Tissue paper is used for wiping. Lots of paper
is also used as packing materials.
(5) Rubber :
Ans. Rubber is used to make tyres
of all vehicles. For this hard, vulcanized rubber is used. Erasers, rubber toys, balls,
footwear, rubber bands are many articles made from
rubber.
Q 3 Find out:
(1) How is lac obtained from nature ?
Ans. Lac is the secretory material obtained from Lac insect.
From the body of female lac insect this resinous substance is given out as
secretion. When this substance comes in contact with air, it solidifies and
forms lac.
(2) How are pearls obtained ?
Ans. Pearls are formed inside the shells of a bivalve marine
animal. If any foreign particle enters the body of this animal, a layer of
protective substance called chancre is deposited around it. This deposition
ultimately forms pearl. In the laboratories, artificially a bead is inserted in
the body of an animal called Pearl oyster. Pearl oyster deposits layers of
chancre around this bead. This is how cultured pearl is prepared.
Q. 4. Answer the following questions :
(1) Why did the need for man-made
materials arise?
Ans. Man continuously strives for newer and newer things. He
always wants to make his life more comfortable. Therefore from the natural
substances he tried to make different. usable artificial substances. The production
of low cost and plentiful materials satisfy man's need.
(1)
Which are the natural materials
obtained from plants and animals ?
Ans. Following
plant-origin and animal-origin natural materials are obtained : (1)
Plant-origin material: Cotton, jute, hemp, teak, wood, flowers, fruits. (2)
Animal-origin material : Leather, silk, lac, pearl, wool.
(3) What is vulcanization ?
Ans. Vulcanization is a chemical process. In this process,
the rubber is heated with sulphur for three to four hours. This process makes
rubber hard.
(4)Which natural materials are used to obtain fibres ?
Ans. The natural materials used to obtain fibres are cotton,
jute, hemp, wool, silk, etc.
Q. 5. Give
scientific reasons :
(1) We must use
cotton clothes in summer.
Ans. Cotton clothes
are made from natural fibres. The sweat is absorbed in these fibres. The skin
remains dry and the chance of catching skin infection is less by using clothes
made from synthetic fibres, we may feel uncomfortable. Therefore, we must use cotton
clothes in summer.
(2)
We must observe economy in the use
of materials.
Ans. Man has over
used natural resources to satisfy his needs. He also made many new substances
by changing the natural substances in an irreversible way. While making such subtances,
the properties of the constituents undergo change due to chemical reactions we
cannot obtain the natural resource
again Many times these man-made substance are hazardous for the
environment. e.g. thermocol plastic. In order to save our natural resource and prevent its depletion, we must observe
economy in the use of them
(3) Saving paper is the need of the hour.
Ans. Paper is made from wood pulp. To obtain paper, more and
more trees are felled by excessive use of paper, large scale deforestation
takes place. If trees and forests vanish. we have to face dangers such as
climate change. Therefore, saving paper is the need of the hour.
(4) Man-made material has more
demand.
Ans. Man-made material is easy to use, low in cost,
available in plenty. The origin natural materials are changed into man-made
material to suit our convenience. e.g. instead of cotton and wool fibres,
synthetic fibres are more convenient for use. Plastic and thermocol are the
materials that has fast replaced the natural alternatives. Thus man-made material
has more demand.
(5) Humus is a natural material.
Ans. There are soil microbes that bring about decomposition
process in the soil. From the dead and decaying remains of animals and plants
humus is formed by them. This a natural process and therefore humus is called a
natural material.
Q 6 How is paper manufactured? Write
in your own words.
Ans.
(1) For making paper, the pine like coniferous trees are felled. (2) Bark from
the logs of these coniferous tress is removed. (3) The wood is broken into
small pieces. (4) It is mixed with certain chemical and soaked for a long time.
This forms a pulp. (5) When the chemical process is completed, the fibres from
the wood are separated. (6) the dyes are then mixed in the pulp and it is
passed through rollers. (7) It is then dried and then wound on the reels.
