Chapter 6 – Substances in Daily Use
1. Fill in the blanks using proper words.
(a) Rubber made by vulcanization is a ________ material.
Ans: hard
(b) Man-made materials are made by ________ natural materials.
Ans: processing
(c) ________ thread was developed simultaneously in New York and London.
Ans: Nylon
(d) Rayon is also known as ________.
Ans: synthetic silk
2. Answer the following questions.
(a) 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 fulfills man’s needs.
(b) 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.
(c) 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.
(d) Which natural materials are used to obtain fibres?
Ans: The natural materials used to obtain fibres are cotton, jute, hemp, wool, silk, etc.
3. What are we used for?
(a) Soil
Ans: Soil supports all living things on Earth. It is also used to make various articles and as a building material.
(b) Wood
Ans: Wood is used to make furniture, in paper industries and other decorative articles.
(c) Nylon
Ans: It is used for making clothes, ropes, fishing nets, etc.
(d) Paper
Ans: It is used as writing material, for packing and printing currency notes.
(e) Rubber
Ans: It is used for making rubber bands, erasers, toys, tyres, etc.
4. How is paper manufactured? Write in your own words.
Ans:
(1) For making paper, pine-like coniferous trees are felled.
(2) The bark from the logs of these coniferous trees is removed.
(3) The wood is broken into small pieces.
(4) It is mixed with certain chemicals and soaked for a long time. This forms a pulp.
(5) When the chemical process is complete, the fibres from the wood are separated.
(6) The dyes are then mixed in the pulp, which is passed through rollers.
(7) It is then dried and wound on the reels.
5. Give scientific reasons.
(a) We must use cotton clothes in summer.
Ans: Cotton clothes are made from natural fibres. The sweat is absorbed by these fibres. The skin remains dry, and the chance of catching a skin infection is lower. By using clothes made from synthetic fibres, we may feel uncomfortable. Therefore, we must use cotton clothes in the summer.
(b) We must observe economy in the use of materials.
Ans: Due to the needs of the growing population, natural resources are getting depleted. It takes a very long time for these natural materials to be replenished. Therefore, we must observe economy in the use of materials.
(c) Saving paper is the need of the hour.
Ans: Paper is made from wood pulp. To obtain paper, more and more trees are felled. Through 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.
(d) Man-made materials have more demand.
Ans: Man-made material is easy to use, low in cost, and available in plenty. The original natural materials are changed into man-made materials to suit our convenience; e.g., instead of cotton and wood libres, synthetic fibres are more convenient for use. Plastic and thermocol are the materials that have quickly replaced the natural alternatives. Thus, man-made materials have more demand.
(e) Humus is a natural material.
Ans: There are so-called microbes that bring about the decomposition process in the soil. From the dead and decaying remains of animals and plants, humus is formed. This is a natural process, and therefore humus is called a natural material.
6. Find out.
(1) How is lac obtained from nature?
Ans: Lac is the secretory material obtained from Lac insects. From the body of a female lac insect, this resinous substance is given out as a 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 bivalve marine animals. If any foreign particle enters the body of this animal, a protective substance called chancre is deposited around it. This deposition ultimately forms pearls. In the laboratories, an artificial bead is inserted in the body of an animal called the pearl oyster. Pearl oyster deposits layers of crystal around this bead. This is how cultured pearls are prepared.