Class 8 Science Chapter 17 - Man Made Materials Textbook solutions


Important points to remember :
  1. Structure  of all  the  plastics is not  same. Some are linear while some are circular. 
  2. Depending upon the effect  of heat, plastic  can be classified into two types. 
  3. The plastic that can be molded  as per our wish is called  as thermoplastic.  eg. Polythene,  PVC are used for manufacturing  the toys, combs, plates, bowls etc.  
  4. Another plastic  is such that once  a specific  shape is given  with  the  help  of mold, its shape cannot be changed on heating. It is called as thermosetting  plastic.  eg. Electric  switches, coverings over the handles of cookers, etc. 
  5. While glass production, mixture  needs to be heated up to 1500 ºC. During this, green house gases like  sulphur dioxide, nitrogen dioxide, carbon dioxide are released through burning of fuel.


Question 1: Try to find it 
a. Plastic shows ............... property, hence it can be molded to any shape.

b. Motor cars are coated with .................

c. Thermocoal melts  at .............. ∘C.

d. ................ glass dissolves in water.

Answer :
a. Plastic shows plasticity property, hence it can be molded to any shape.

b. Motor cars are coated with Automotive paint.

c. Thermocoal melts  at more than 100∘C.

d. Alkali silicate glass dissolves in water.



Question 2: Who is my partner ?
  'A' column    'B' column
 a. Lead glass i. Plates
 b. Bakelite          ii. Mattresses
 c. Thermocol iii. Electric bulb
 d. Optic glass iv. Electric switch
 e. Polypropylene  v. Lens

Answer :

 a. Lead glass - Electric bulb
 b. Bakelite        -  Electric switch
 c. Thermocol - Plates
 d. Optic glass - Lens
 e. Polypropylene - Mattresses



Question 3: Answer the following.
a. Thermocol is produced from which matterial ?
Answer : Thermocol is a form of a complex  material  called  polystyrene.  It transforms in to liquid state on heating  at more than 100 ºC temperature  and returns to solid state on cooling.  Due to this, we can give any desired shape to it. Being a good shock-absorber, it is used in packing of delicate items.

b. Write uses of PVC.
Answer : Economical, versatile polyvinyl chloride (PVC, or vinyl) is used in a variety of applications in the
  1. building and construction, 
  2. health care, 
  3. electronics, 
  4. automobile and other sectors, 
  5. in products ranging from piping and siding, 
  6. blood bags and tubing, 
  7. to wire and cable insulation, 
  8. windshield system components and more. 


c. Write the natural or manmade row material of the following items. Matteress,  beaker,  bangle,  chair,   gunny bag,  knife,  pen
Answer : 
Mattress plasticity - Thermoplastic (Polypropylene)

Beaker - Silica glass

Bangle - Gold, silver, platinum, glass, wood, plastic

Chair - Thermoplastic (Polypropylene)

Gunny bag - Hessian (burlap) formed from jute broom, Plastic, corn husks

Knife - Carbon steel, stainless steel, cobalt and titanium alloys

Pen -Brass which is an alloy of copper and zinc

d. Which are the main ingredients of glass ? 
Answer : Main ingredients of glass are as follows:
  1. Sand or Silica
  2. Sodium Carbonate
  3. Lime or Calcium Oxide
  4. Other Additives
  5. Lead glass: mixture of sand, soda, limestone and lead oxide
  6. Silica glass: using silica only
  7. Borosilicate: mixture of sand, soda, boric acid, aluminium oxide
  8. Alkali silicate glass: mixture of sand, soda

​e. How the plastic is produced ?
Answer : It starts with raw materials, such as natural gas, oil or plants, refined into ethane and propane. Ethane and propane are treated with high heat, in a process known as cracking. This is how they’re converted into monomers such as ethylene and propylene. The polymer is fed into an extruder, where it is melted and fed into a pipe. The plastic forms a long tube as it cools.


Question 4.  Distinguish between. 
a. Manmade material and natural material 
Answer : Natural materials are sourced directly from nature -- cotton is picked from cotton plants, corn harvested from corn fields and granite is mined from quarries. Man-made materials, on the other hand, go through rigorous processing to alter the material so that it suits its intended purpose.

b. Thermoplastic and thermosetting plastic.
Answer : Thermoplastics. Though thermoset plastics and thermoplastics sound similar, they have very different properties and applications. The primary physical difference is that thermoplastics can be remelted back into a liquid, whereas thermoset plastics always remain in a permanent solid state.


Question 5: Answer the following in your words.

a. Explain the effect of following materials on environment and human health.
1. Plastic
2.Glass
3.Thermocol.

1. Plastic 
Answer : Plastic has toxic pollutants that damage the environment and cause land, water, and air pollution. It can take hundreds or even thousands of years for plastic to break down, so the damage to the environment is long-lasting. Chemicals added to plastics are absorbed by human bodies. Some of these compounds have been found to alter hormones or have other potential human health effects. Plastic debris, laced with chemicals and often ingested by marine animals, can injure or poison wildlife.

2.Glass 
Answer : The major environmental impact of glass production is caused by atmospheric emissions from melting activities. The combustion of natural gas/fuel oil and the decomposition of raw materials during the melting lead to the emission of CO2. This is the only greenhouse gas emitted during the production of glass.

3. Tharmacol 
Answer : Styrofoam is manufactured by using HFCs, or hydrofluorocarbons, which have negative impacts on the ozone layer and cause global warming. thermocol sheets are injurious to health as they are not properly sterilised and can also contaminate the food served in them. As a result, people may be affected by bacterial infections, skin allergies and gastro problems. These are very light weight which floats on water, they cause marine debris. A small portion of thermocol waste is only being compressed and reused.


b. Which measures will you arrange to minimize the environmental problems arising due to non-degradable plastic ?
Answer : measures will you arrange to minimize the environmental problems arising due to non-degradable plastic are as follows:

  1. We must reduce our plastic dependency:
  2. Increase fees and taxes on polluting plastics:
  3. Increased waste management where the problem is greatest:
  4. Increased mapping, surveillance and research




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