Class 8 Basic Science Chapter 15 Important Questions Kerala Syllabus Chemistry of Matter

The comprehensive approach in SCERT Class 8 Basic Science Textbook Solutions Chapter 15 Chemistry of Matter Important Questions ensure conceptual clarity.

Chemistry of Matter Extra Questions and Answers Class 8 Basic Science Chapter 15 Kerala Syllabus

Chemistry of Matter Class 8 Important Questions

Question 1.
Match the polymer type in Column A with its characteristic in Column B.

Column A	Column B
(i) Thermoplastic	(a) Cannot be remelted and reshaped.
(ii) Thermosetting Plastic	(b) Can be reheated and reshaped multiple times.
(iii) Fibre	(c) Polymer with elastic nature.
(iv) Rubber	(d) Polymer suitable for making strong threads.

Answer:
(i) – b, (ii) – a, (iii) – d, (iv) – c

Column A	Column B
(i) Thermoplastic	(b) Can be reheated and reshaped multiple times.
(ii) Thermosetting Plastic	(a) Cannot be remelted and reshaped.
(iii) Fibre	(d) Polymer suitable for making strong threads.
(iv) Rubber	(c) Polymer with elastic nature.

Question 2.
Match the type of glass in Column A with its major use in Column B.

Column A	Column B
(i) Soda lime glass	(a) Lenses, prisms
(ii) Borosilicate glass	(b) Window glass, bottles
(iii) Flint glass	(c) Laboratory equipment, cookware

Answer:
(i) – b, (ii) – c, (iii) – a

Column A	Column B
(i) Soda lime glass	(b) Window glass, bottles
(ii) Borosilicate glass	(c) Laboratory equipment, cookware
(iii) Flint glass	(a) Lenses, prisms

Question 3.
Match the chemical added to glass in Column A with the colour obtained in Column B.

Column A	Column B
(i) Cobalt oxide	(a) Yellow
(ii) Chromium oxide	(b) Ruby red
(iii) Cadmium sulphide	(c) Blue
(iv) Gold chloride	(d) Green

Answer:
(i) – c, (ii) – d, (iii) – a, (iv) – b

Column A	Column B
(i) Cobalt oxide	(c) Blue
(ii) Chromium oxide	(d) Green
(iii) Cadmium sulphide	(a) Yellow
(iv) Gold chloride	(b) Ruby red

Question 4.
Statement (i): Thermoplastics can be reheated and reshaped.
Statement (ii): Thermosetting plastics can also be reheated and reshaped.
(a) Both statements (i) and (ii) are correct.
(b) Statement (i) is correct, but statement (ii) is incorrect.
(c) Statement (ii) is correct, but statemeht (i) is incorrect.
(d) Both statements (i) and (ii) are incorrect.
Answer:
(b) Statement (i) is correct, but statement (ii) is incorrect. (Thermosets cannot be reshaped after setting).

Question 5.
Statement (i): Nylon is the first synthetic fibre made by humans.
Statement (ii): Natural rubber is obtained from the latex of the rubber tree.
(a) Both statements (i) and (ii) are correct.
(b) Statement (i) is correct, but statement (ii) is incorrect.
(c) Statement (ii) is correct, but statement (i) is incorrect.
(d) Both statements (i) and (ii) are incorrect.
Answer:
(a) Both statements (i) and (ii) are correct.

Question 6.
Statement (i): Silica (SiO₂) is the major component present in all common types of glass.
Statement (ii): Glass is considered a natural material.
(a) Both statements (i) and (ii) are correct.
(b) Statement (i) is correct, but statement (ii) is incorrect.
(c) Statement (ii) is correct, but statement (i) is incorrect.
(d) Both statements (i) and (ii) are incorrect.
Answer:
(b) Statement (i) is correct, but statement (ii) is incorrect. (Glass is a synthetic material).

Question 7.
Define Polymerisation, Monomer, and Polymer.
Answer:
Polymerisation: The process in which many small molecules combine under high pressure and temperature to form large molecules.
Monomers: The small molecules used in polymerisation.
Polymers: The large molecules formed by the combination of a large number of monomers.

Question 8.
Explain the ‘4R’ approach recommended to reduce plastic pollution.
Answer:
The 4R approach consists of:
Refuse: Avoid giving or accepting plastic products.
Reduce: Minimise the use of plastic products.
Reuse: Reuse plastic products multiple times.
Recycle: Convert plastic products into new items.

Question 9.
Why are synthetic rubbers often preferred over natural rubber for making tyres?
Answer:
Synthetic rubbers generally show less wear and tear compared to natural rubber, making them more durable and suitable for the demanding conditions tyres face.

Question 10.
How can you identify the type of plastic used in a container using the identification code?
Answer:
Look for the recycling symbol (chasing arrows) on the plastic item. Inside the symbol, there will be a number from 1 to 7. This number corresponds to a specific type of plastic resin (e.g., 1 is PET, 2 is HDPE, 3 is PVC, etc.). You can then refer to a chart (like Table 15.6) to find the abbreviation and name of the plastic.

Question 11.
Describe the observation when a thermoplastic material (like polythene) and a thermosetting material (like Bakelite) are heated strongly after being initially shaped.
Answer:
Thermoplastic: When heated strongly, the thermoplastic material will soften, melt, and can be reshaped.

Thermosetting plastic: When heated strongly, the thermosetting material will not soften or melt. It may char or decompose at very high temperatures but cannot be reshaped.

Question 12.
A student observes the characteristics of natural cotton fibre and synthetic polyester fibre. What differences would they likely note regarding water absorption and durability?
Answer:
Water absorption: The natural cotton fibre would show more water absorption ability compared to the synthetic, polyester fibre.

Durability: The synthetic polyester fibre would likely show more durability (resistance to wear and tear) compared to the natural cotton fibre.

Question 13.
What is the main chemical compound in sand that reacts with metal salts at high temperatures to form glass?
Answer:
Silicon dioxide (SiO₂).

Question 14.
Identify the polymer formed when many ethylene monomers undergo polymerisation.
Answer:
Polyethylene (or Polythene). (The name implies it’s formed from ethylene).

Question 15.
What type of substance is generally formed when silicon dioxide (SiO₂) reacts with metal salts (like sodium carbonate) at high temperature?
Answer:
Glass.

Question 16.
Write the chemical formula for Silica, the main component of glass.
Answer:
SiO₂

Question 17.
Write the full name for the plastic represented by the abbreviation PVC.
Answer:
Polyvinyl chloride.

Question 18.
Observe Figure 15.6, which shows monomers combining to form a polymer. Explain why the molecular mass of a polymer is much higher than that of its monomer.

Answer:
A polymer is formed by chemically combining a large number of individual monomer molecules into a long chain. Therefore, the total mass of the polymer molecule is essentially the sum of the masses of all the monomer units that joined together, making it significantly higher than the mass of a single monomer.

Question 19.
Differentiate between thermoplastic and thermosetting plastic.
Answer:
The plastic that get softened on heating and hardened on cooling is thermoplastics. When heating physical change occurs.

The plastic which remains soft when heated and gets hardened permanently on cooling is thermosetting plastics. Chemical change occurs when heating.

Question 20.
Given some occasions of using plastic. Find the peculiarity of plastic used and fill the table.

Occasion	Peculiarity
As the covering of conductor
To make the handles of cooking vessels
To keep chemicals
To make water tanks
To make house hold materials

Answer:

Occasion	Peculiarity
As the covering of conductor	Plastics are insulators
To make the handles of cooking vessels	Not conducting heat
To keep chemicals	Do not react with chemical
To make water tanks	No rusting. Less weight
To make house hold materials	Easy touse. Less weight

Question 21.
Write 4 occasions which plastic is harmful to daily life.
Answer:

1. Enviromental pollution when it is thrown without any control.
2. When burning air pollution.
3. Hindrance in drainages
4. The water absorption property of soil decreases when plastics are dumped in soil.

Question 22.
What are the uses of plastic in the field of human health?
Answer:

• To produce I V tubes, bottles
• To produce heart valves
• To produce packets

Question 23.
What are the uses of plastic in the field of production of house building.
Answer:
To produce roof materials, doors, plumping and wiring materials.

Question 24.
List the peculiarities of plastic.
Answer:
Can mould in any shape, longlasting, Insulator, do not conduct heats, not reacting with chemicals and water, will burn.

Question 25.
Separate natural and artificial polymer from the list Rubber, wool, p.v.c, Bakelite, nylon, rayon cellulose, silk, polythene, polyester
Answer:

Natural	Artificial
Rubber	p.v.c
Wool	polythene
Cellulose	nylon
Silk	rayon
	Polyester

Question 26.
List the merits of natural and artificial polymer.
Answer:

Merits	Demerits
Comfortable to wear	Less availability
More aeration	wrinkle easily
Absorb water, sweat	high cost
Not easily burns	not durable

Question 27.
If we heat polyethene cover can we convert into earlier stage? Justify.
Answer:
No. Undergoes chemical change because it is thermosetting plastic.

Question 28.
The primary component present in all common types of glass is:
a. Calcium oxide (CaO)
b. Lead oxide (PbO)
c. Silica (SiO₂)
d. Sodium oxide (Na₂O)
Answer:
c. Silica (SiO₂)

Question 29.
The small molecules that combine in a process called polymerisation to form a very large molecule are known as:
a. Isomers
b. Polymers
c. Monomers
d. Dimers
Answer:
c. Monomers

Question 30.
Which of the following is a Thermosetting Plastic?
a. Polythene
b. PVC
c. Bakelite
d. PET
Answer:
c. Bakelite

Question 31.
The plastic recycling code ‘2’ with the abbreviation HDPE is used for:
a Polyvinyl Chloride
b. Low-Density Polyethylene
c. High-Density Polyethylene
d. Polystyrene
Answer:
c. High-Density Polyethylene

Question 32.
Which chemical is typically added to molten glass to achieve a Ruby Red colour?
a. Cobalt oxide
b. Chromium oxide
c. Cadmium sulphide
d. Gold chloride
Answer:
d. Gold chloride

Question 33.
Explain why Borosilicate Glass is the preferred material for making laboratory equipment like beakers and flasks, rather than Soda-lime glass.
Answer:
Borosilicate Glass is preferred because it contains Boric acid/Boric oxide. This gives it a low coefficient of thermal expansion which makes it highly resistant to heat and thermal shock, preventing it from cracking when heated or cooled rapidly.

Question 34.
Differentiate between Thermoplastics and Thermosetting Plastics based on their ability to be reshaped and provide one example of an object made from each.
Answer:
Thermoplastics: Can be reheated, melted, and reshaped.
Example: Polythene/PVC.
Thermosetting Plastics: Cannot be reheated and melted/reshaped.
Example: Bakelite/Pressure cooker handle.

Question 35.
State and briefly explain the 4R approach that is essential for resolving the problem of plastic pollution in our environment.
Answer:
The 4R Approach is:

1. Refuse: Avoid single-use disposableplastic products.
2. Reduce: Minimise overall plastic usage.
3. Reuse: Find new ways to use plastic products instead of discarding them.
4. Recycle: Convert waste plastic into new usable items through suitable processes.

Question 36.
Analyse the properties of polymers by completing the following table and answering the question below.

Category/Type	Example Polymer	Key Property or Characteristic
Natural Polymer	(i) ____________	A component of wood and paper. A component of wood and paper.
Fibre Polymer	Nylon	(iii)  ____________ (excluding its use in clothing)
Glass Type	Flint Glass	(iii) ____________
Thermoset Plastic	(iv)  ____________	Key Property or Characteristic

Cannot be reheated and molded into a new shape.
What is the primary advantage gained by blending a natural fibre like Cotton with a synthetic fibre like Nylon?
Answer:
(i) Cellulose or Natural Rubber
(ii) Strong and long threads/Low wear and tear/High durability (Any one appropriate property of a fibre)
(iii) High refractive index (Used for lenses and prisms)
(iv) Bakelite or Melamine (Any one appropriate thermoset)
The advantage is to combine the best properties of both. Specifically, it provides the comfort and water absorption of cotton with the strength, durability, or wrinkle resistance of nylon.