NCERT Solutions for Class 8th Science

Chapter 3 – SYNTHETIC FIBRES AND PLASTICS

(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)

 

Q.1      Explain why some fibres are called synthetic.

Ans     Fibres are called synthetic because they are not obtained from plants or animals i.e. are not natural                      fibres and are prepared by human beings through chemical processes. They are also called artificial or                  man-made fibres. It is a chain of large units called polymer joined together. Eg. rayon, nylon, polyester                and acrylic etc.

Q.2      Mark (√ ) the correct answer:

           Rayon is different from synthetic fibres because

           (a) it has a silk like appearance

           (b) it is obtained from wood pulp

           (c) its fibres can also be woven like those of natural fibres

Ans     (b) it is obtained from wood pulp

Q.3      Fill in the blanks with appropriate words:

          (a) Synthetic fibres are also called ______ or _______ fibres.

          (b) Synthetic fibres are synthesised from raw material called ________.

          (c) Like synthetic fibres, plastic is also a __________.

Ans    (a) Synthetic fibres are also called _artificial_ or _man-made_ fibres.

          (b) Synthetic fibres are synthesised from raw material called _petrochemicals_.

          (c) Like synthetic fibres, plastic is also a _polymer_.

Q.4      Give examples which indicate that nylon fibres are very strong.

Q.5      Explain why plastic containers are favoured for storing food.

Q.6      Explain the difference between the thermoplastic and thermosetting plastics.

Q.7      Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Q.8      Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Q.9      Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Q.10    Give examples to show that plastics are noncorrosive in nature.

Ans     Plastics are noncorrosive in nature. The following examples explain the same:

            1) Sanitary cleaners and acids are stored in plastic bottles.

            2) They are used to store various kind of chemicals as they are non corrosive.

            3) Materials like pickles (which contain acid) are packed in plastics as they do not harm plastics.

Q.11      Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Ans     No. This is because the handle undergoes a lot of stress and needs to be made of hard and strong                           material to provide a.....................

Q.12      ‘Avoid plastics as far as possible’. Comment on this advice.

Q.13      Match the terms of column I correctly with the phrases given in column II.

  Column I                                                Column II

(i) Polyester                             (a) Prepared by using wood pulp

(ii) Teflon                                (b) Used for making parachutes and stockings

(iii) Rayon                               (c) Used to make non-stick cookwares

(iv) Nylon                                (d) Fabrics do not wrinkle easily

Q.14     ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Ans     Synthetic fibres are man-made fibres prepared from petrochemicals. They are not obtained from plants               and hence cutting of trees i.e. deforestation is not required for them which was a necessity in case of                     natural fibres. Hence manufacturing synthetic fibres is actually helping conservation of forests.

Q.15      Describe an activity to show that thermoplastic is a poor conductor of electricity.