Samacheer Kalvi 7th Science Term 3 Unit 3 Book Back Questions and Answers:
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Science – Term 3
Unit 3 – Polymer Chemistry
I. Choose the correct answers:
1. The first man-made fibre is ________
(a) Nylon
(b) Polyester
(c) Rayon
(d) Cotton
Answer: (c) Rayon
2. Which of the following is the strongest?
(a) Rayon
(b) Nylon
(c) Acrylic
(d) Polyester
Answer: (b) Nylon
3. When you place a natural fibre in a flame it ________
(a) melts
(b) burns
(c) gets nothing
(d) explodes
Answer: (b) burns
4. A synthetic fibre that has similar properties to wool is ________
(a) Nylon
(b) Polyester
(c) Acrylic
(d) PVC
Answer: (c) Acrylic
5. A good application of plastic is the use of ________
(a) Blood bags
(b) Plastic cutlery
(c) Plastic straws
(d) Plastic carry bag
Answer: (a) Blood bags
6. ________ is a non-biodegradable material.
(a) Paper
(b) A plastic bottle
(c) Cotton cloth
(d) Wool
Answer: (d) Wool
7. PET is the acronym for ________
(a) Polyester
(b) Polyester and terylene
(c) Polyethylene terephthalate
(d) Polyetheneterylene
Answer: (c) Polyethylene terephthalate
II. Fill in the blanks:
- ______ is an example of polyester fabric.
- ______ are used to identify different types of plastics.
- A ______ is a long chain made up of many repeated small units called monomers.
- The fully natural fibre is called ______
- A natural fibre obtained by boiling cocoons is called ______
Answer:
- Raincoat
- Resin codes
- polymer
- plant fibre
- silk
III. True or False:
1. A lot of plastic pollutes our environment.
Answer: True.
2. Refuse (avoid) is the best way to manage plastic.
Answer: True.
3. It is good to wear clothes made of synthetic fibres while cooking.
Answer: (False)
Correct statement: It is good to wear clothes made of fibres while cooking.
4. Degradable plastics break down into tiny pieces called microplastics.
Answer: True.
5. Cotton is a natural polymer.
Answer: True.
IV. Match the following:
| A | B |
| 1. Nylon | Thermoplastic |
| 2. PVC | Thermosetting plastic |
| 3. Bakelite | Fibre |
| 4. Teflon | Wood pulp |
| 5. Rayon | Non-stick cookwares |
Answer:
| A | B |
| 1. Nylon | Fibre |
| 2. PVC | Thermoplastic |
| 3. Bakelite | Thermosetting plastic |
| 4. Teflon | Non-stick cookwares |
| 5. Rayon | Wood pulp |
V. Arrange in Correct Sequence:
1. Mix water, starch, vinegar, and glycerin in a cooking pot.
2. Let the article cool for 24 hours before we use it.
3. Shape the material to form a cup or bowl.
4. Continuously mix on medium heat until the liquid turns clear.
5. When the liquid begins to bubble it is ready to be taken off the stove.
6. Spread the gel onto aluminum foil and cool.
Answer:
1. Mix water, starch, vinegar and glycerin in a cooking pot.
4. Continuously mix on medium heat until the liquid turns clear.
5. When the liquid begins to bubble it is ready to be taken off the stove.
6. Spread the gel onto aluminium foil and cool.
3. Shape material to form a cup or bowl.
2. Let the article cool for 24 hours before we use it.
VI. Analogy :
1. Cotton: natural:: Polyester: ______
Answer: Synthetic.
2. PLA spoon :compostable:: Plastic spoon: ______
Answer: Disposable.
3. Nylon: melts on heating:: Silk: ______
Answer: Burns on heating.
VII. Assertion – Reason type question :
Option:
a. Both A and R are true and R is the correct explanation of A.
b. Both A and R are true but R is not the correct explanation of A.
c. A is true but R is false.
d. A is false but R is true.
Question 1.
Assertion (A): Vegetable peels buried in the soil disappear within two weeks.
Reason (R): Vegetable peels are compostable.
Answer: (a) Both A and R are true and R is the correct explanation of A
2. Assertion (A): It takes a very long time for nylon clothes to breakdown into microfibers but cotton clothes need only six months to decompose.
Reason (R): Nylon made out of petrochemicals is non-biodegradable and cotton cloth is biodegradable.
Answer: (a) Both A and R are true and R is the correct explanation of A
3. Assertion (A): It is good to avoid plastics.
Reason (R): Plastics end up polluting the environment.
Answer:
(a) Both A and R are true and R is the correct explanation of A
VIII. Short Answer:
1. What does the term biodegradable mean?
Answer:
A material that gets decomposed through natural processes and action by bacteria is called biodegradable
2. What kind of fabric is suitable to dress up and play with in summer? Why?
Answer:
- In summer it is better to wear clothing that is made out of cotton materials rather than synthetic.
- This is because most synthetic fibres absorb very little moisture and do not allow air circulation making them hot and uncomfortable to wear.
3. How do plastics impact animals and the environment?
Answer:
- The increase in the use of plastics, particularly the one-time use, and throw-away plastics has serious impacts on the environment, animals, and our health.
- We have seen garbage dumps with different plastics. One big problem with plastics is that they do not decompose or biodegrade.
- This leads to large amounts of waste that will not disappear and end up accumulating and polluting the environment.
- Many animals confuse plastic for food and eat it by accident. When leftover food is thrown away it is often packed in plastic. Animals smell the leftover food and eat the plastic by accident.
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