BASIC SCIENCE FOR CLASS 8 AMARNATH MISHRA,PHD GEETA MEHTA ,PHD DEEPTI LEHRI,PHD RAJESH MOHAN, PHD

               Chemistry

               Ch- 1

              Synthetic Materials

             Only answer 

           Exercises

A. Answer the following in not more than 20 words

1. A polymer is a large molecule made up of many smaller molecules called monomers.

2. Polymerization.

3. Viscose rayon, acetate rayon, and cuprammonium rayon. 

4. Ropes, nets, filters, brushes, and artificial turf.

5. Plastics are materials that are made from polymers.

6. Polyisobutylene, polystyrene, and polyvinyl chloride.

7. Polyethylene, polypropylene, and polyvinyl chloride.

8. The ability of a material to resist being pulled apart.

9. (a) Hydrophilic materials, 

(b) hydrophobic materials

B. Answer the following in note more than 40 words. 

1. Acrylics are not spun from the melt because they are thermosetting plastics, which means they cannot be melted and reshaped after they have been formed.

2. Thermoplastics are plastics that can be melted and reshaped multiple times, while thermosetting plastics cannot be melted and reshaped after they have been formed.

3. Propylene and acetylene can be used to make a variety of products, including plastics, fibers, and chemicals. 

C. Answer the following in note more than 100 words. 

1. Polymers are classified into natural polymers and synthetic polymers. Natural polymers are found in nature, such as cellulose, proteins, and starch. Synthetic polymers are made by humans, such as nylon, polyester, and polyethylene. The raw materials used to manufacture synthetic polymers are oil, natural gas, and coal.

2. Three advantages of synthetic fibers in comparison to natural fibers are:

    * They are stronger and more durable.

    * They are less expensive to produce.

    * They can be made in a variety of colors and textures.

Three disadvantages of synthetic fibers in comparison to natural fibers are:

    * They are not as breathable as natural fibers.

    * They can be more irritating to the skin.

    * They are not biodegradable.

3. To compare the tensile strengths of threads of different materials, you can use a tensile testing machine. This machine will apply a force to the thread until it breaks. The amount of force required to break the thread is the tensile strength of the thread. 

D. Complete the following. 

1. Acrylic fibres compete with wool.

2. Polythene carrybags clog drains and sewers.

3. Plastics are generally non-biodegradable substances. 1.e., they are not environmentally broken down to simpler, harmless substances.

4. On being burnt, plastics give harmful gases like carbon monoxide, dioxins, and furans.

5. Nylon has a higher tensile strength than cotton.

6. On being heated, polyester and nylon melt before they burn

E. Choose the correct option in each of the following.