Apart from textbook, students should also refer to these NCERT solutions to know the best answers to the respective questions. Apart from science, students can also check NCERT solutions for class 8 science and prepare in a more effective way for the final exams.
CBSE NCERT Solutions for Class 8 Science Chapter 3:
Explain why the following are made of thermosetting plastics.
a) Saucepan handles.
b) Electric plugs/switches/plug boards.
a) Saucepan handles are made of thermosetting plastics because these plastics do
not get softened on heating. Also, thermosetting plastics such as Bakelite are poor
conductors of heat. So it is easier to handle the utensil while cooking.
b) Electrical plugs, switches and plug-boards are made up of thermosetting plastics
because it is a bad conductor of electricity. It does not allow the electric current to pass through it, thus safe in using in electric appliances.
Give examples to show that plastics are non-corrosive in nature.
Plastics are not corroded even if they come in contact with strong chemicals. This
is because of their non-reactive nature with most materials. For example:
i) Plastics don't react with acids or bases which are kept in them. The cleansing chemicals that we use at home are stored in plastic bottles, instead of metal containers.
ii) Plastics don't react with air and water. For example: chairs, buckets all are made from plastics.
Avoid plastics as far as possible. Comment on this advice.
We should avoid plastics because:
i) Plastics are non-biodegradable. Once introduced into the environment, they take
several years to decompose. Plastics cause environmental pollution.
ii) They cannot be burnt as when burnt, they release poisonous gases. Plastic bags
thrown in the garbage dump are swallowed by animals like cows. These bags choke their respiratory system and can even prove fatal. Therefore, we should avoid plastics as far as possible.
Manufacturing synthetic fibres is actually helping conservation of forests. Comment.
The natural fibers are obtained from plants and animals, whereas the synthetic
fibers are obtained by chemical processing of petrochemicals. Unlike natural fibers, manufacturing of synthetic fibers do not require to cut trees or hunting of any animal. In this way manufacturing synthetic fibers is actually helping conservation forests.