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

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Class 8 Basic Science Chapter 15 Chemistry of Matter Question Answer Notes

Class 8 Basic Science Chapter 15 Notes Kerala Syllabus Chemistry of Matter Question Answer

Chemistry of Matter Class 8 Questions and Answers Notes

Let’s Assess

Question 1.
Which of the following is made of a synthetic material?
a. Iron nail
b. Aluminium vessel
c. Glass test tube
d. Gold ornament
Answer:
W c. Glass test tube.
Reason: Glass is a synthetic material made by reacting silica (sand) with metal salts at high temperatures. Iron, Aluminium, and Gold are metals derived from natural sources.

Question 2.
Which of the following is not a polymer?
a. Bakelite
b. PVC
c. Rubber
d. Copper
Answer:
d. Copper.
Reason: Bakelite, PVC, and Rubber (natural or synthetic) are polymers, which are large molecules formed from repeating smaller units called monomers. Copper is a metallic element.

Question 3.
What is the difference between thermoplastics and thermosets?
Answer:
The main difference lies in their response to heat after moulding:
Thermoplastics (like polythene) can be reheated, melted, and reshaped into new products multiple times.
Thermosetting plastics (or thermosets, like Bakelite) cannot be reheated and melted to make new reshaped products once they are set.

Question 4.
Write one reason why synthetic rubber is used in the manufacture of tyres.
Answer:
Synthetic rubber shows less wear and tear compared to natural rubber, making it more durable for use in tyres.

Question 5.
What is the advantage of blending natural fibres along with synthetic fibres?
Answer:
Blending is done to overcome the limitations of both types of fibres. For example, blending cotton (natural) with polyester (synthetic) can create a fabric that has the comfort and breathability of cotton but the durability, wrinkle resistance, and quick-drying properties of polyester.

Question 6.
“Material chemistry provides us with both advantages and disadvantages” Do you agree with this statement? Why?
Answer:
B Yes, I agree with the statement. Advantages: Material chemistry has transformed various natural substances into countless useful products that have improved our quality of life, such as glass for various applications, durable plastics, elastic rubbers, versatile fibres, medicines, soaps, paints, etc.. It plays a crucial role in human progress by creating new materials with suitable properties.

Disadvantages: The production and uncontrolled use of some synthetic materials, particularly plastics, lead to significant environmental problems like plastic pollution. This pollution affects soil, water, and air, harming plants, animals, and ecosystems. Disposal of these materials is often difficult as many are not easily biodegradable.

Basic Science Class 8 Chapter 15 Question Answer Kerala Syllabus

Textbook Page No : 245 & 246

Question 1.
Why does the panchayat give importance to the conservation of water resources? (Discussion)?

Answer:

Items made from natural materials	Items made from synthetic materials
Door – Made of wood	Jar – Made of glass
Chair (wicker) – Made of cane/ rattan	Chair (plastic) – Made of plastic
Rope (jute/coir) – Made of natural fibers	Tyre – Made of synthetic rubber/ plastic
Hammer handle – Made of wood	Bucket – Made of plastic
Vessels (steel) – Made from processed metals	Balloons – Made of rubber/latex (can be natural or synthetic)
Tiffin carrier (steel) – Made from processed metals	Rope (nylon) – Made of synthetic fiber

Question 2.
Try writing down the items made of glass:

Answer:
Mirror

1. Glass jar
2. Windows/Panes
3. Car windshields
4. Beakers and laboratory equipment
5. Bottles
6. Light bulbs
7. Spectacle lenses
8. Lenses
9. Prisms

Textbook Page No : 247

Question 3.
Are the glasses used to make the objects shown in the picture of the same type?
Answer:
No, they are not of the same type. Different types of glass are manufactured by modifying the chemical composition to achieve specific properties for various applications (e.g., thermal resistance for ovenware, or specific refractive index for lenses).

Question 4.
Why can water be used for so many purposes?
Answer:
Water can be used for so many purposes primarily because of its special property as a universal solvent. Water can dissolve a wide variety of substances , and the nature of the water changes depending on what is dissolved in it, allowing it to be used to make different types of solutions. This solubility is one of the main reasons for its varied uses.

Question 5.
Haven’t you seen the shattered glasses of vehicles met with accidents? What is special about them?
Answer:
The glasses used in most vehicle wind-screens (front windshields) are usually Laminated glass, and sometimes side/ rear windows are Tempered glass.

• Laminated glass is special because it is made of two layers of glass bonded by a plastic inner layer (PVB). When it shatters, the fragments stick to the plastic, preventing sharp pieces from flying and causing injury.
• Tempered glass shatters into small, blunt, granular fragments instead of large, sharp shards, which reduces the risk of injury.

Question 6.
Do you know the name of glass used in the display of mobile phones?
Answer:
display of most modern mobile phones is covered with a type of chemically strengthened Aluminosilicate glass (e.g., Gorilla Glass or Dragontrail Glass). It is chosen for its superior scratch resistance and toughness.

Question 7.
Table Completion (Table 15.2)

Answer:

Types of Glasses	Uses	Major Components
Soda-lime glass/Soft glass	To make mirrors, window glass, bottles, etc.	Silica, Sodium oxide, Calcium oxide
Borosilicate Glass	To make laboratory equipment, cookwares, etc.	Silica, Boric acid (or Boric oxide), Sodium oxide, Aluminium oxide
Flint Glass /Optical Glass	Used in the manufacture of lenses, prisms, etc.	Silica, Lead oxide, Potassium oxide
Quartz glass	Apparatus used in chemical laboratories, electric bulbs.	Silica

Question 8.
Which is the component present in ail types of glass?
Answer:
Silica (SiO₂). It is the primary glass-forming material in almost all commercial types of glass.

Question 9.
Find out the other components present in each type of glass.
Answer:
The main components besides Silica are:
Soda-lime glass: Sodium oxide (Na₂O) and Calcium oxide (CaO).
Borosilicate glass: Boric acid/Boric oxide (B₂O₃), Sodium oxide (Na₂O), and Aluminium oxide (Al₂O₃).
Flint Glass/Optical Glass: Lead oxide (PbO) and Potassium oxide (K₂O). (In modern, lead-free flint glasses, lead oxide is sometimes replaced by oxides of Titanium or Zirconium.)

Textbook Page No : 248 & 249

Question 10.
Try writing down the common properties of glass:
Answer:
Based on the nature and uses of glass, the common properties are:

1. Transparency
2. Amorphous (non-crystalline solid)
3. Brittle (breaks suddenly)
4. Chemically resistant (to most common chemicals)
5. Poor conductor of heat and electricity

Question 11.
Haven’t you seen glasses of different colours? How do they get their colour?
Answer:
Glasses get a variety of colors when different chemicals (usually metal oxides) are added during the manufacturing process. These chemicals mix into the molten glass and impart a specific hue.

Question 12.
Why does the molecular mass increase when monomers participate in polymerisation? Can you observe and explain that from the above picture?

Answer:
The molecular mass increases significantly because monomers (small molecules) chemically combine under high pressure and temperature to form a single, very large molecule called a polymer.
Explanation from the picture (Fig 15.6): The diagram illustrates that the Dimer is formed by combining two Monomers, and the Polymer is formed by joining many Monomers in a long chain. The final polymer molecule is simply the accumulated mass of all the individual monomers, resulting in a much higher molecular mass compared to the initial molecules.

Monomer and Polymer

Question 13.
Plastic tables, chairs, etc. can be manufactured easier than wooden ones. Why?
Answer:
Plastic items are easier to manufacture because plastics are polymers that are generally thermoplastics. This means they can be easily melted and molded into complex shapes and designs using industrial processes (like injection molding) in a continuous and rapid manner. Manufacturing wooden objects requires more complex processes like cutting, carving, and joining.

Textbook Page No : 250 & 251

Question 14.
Plastics are widely used due to their unique properties compared to natural materials:
Answer:

1. Can be reshaped (miss)
2. Lightweight
3. Durable
4. Often resistant to chemicals
5. Can be electrical insulators
6. Can be moulded into various shapes easily

Question 15.
Are most of the objects we use daily, natural or synthetic? Discuss.
Answer:
Most of the objects we use daily are made of synthetic materials (polymers like plastics) or contain major synthetic components. While natural materials (like wood, metal, cotton) are still essential, synthetic polymers are favored for massproduced items because they are:

• Less expensive to produce.
• Lightweight and durable.
• Easily molded into various shapes (versatility).
• Resistant to moisture and decay.

Question 16.
How can we identify different types of plastics? What do they indicate?
Answer:
We identify different types of plastics using the Recycling Symbols. These are symbols consisting of a triangle made of chasing arrows, with a number (1 – 7) inside and an abbreviation below

These symbols indicate:

1. The specific type of polymer the item is made from (e.g., PET, PVC, HDPE).
2. The recyclability of the material and how it should be sorted for recycling.

Textbook Page No : 252 & 253

Question 17.
Analysis and Debate: Plastic – Friend or Foe?
Answer:
The discussion revolves around the necessary regulation of plastics in addition to the 4R method (Refuse, Reduce, Reuse, Recycle).

Aspect	Argument (Plastic)	Justification
Friend (Advantages)	Plastic is essential and unavoidable.	Used for diverse benefits. Essential for modern life (e.g., packaging, cables, pipes, bottles.
Foe (Disadvantages)	Uncontrolled use causes environmental damage.	Accumulates and causes water and soil pollution. Alters the natural chemical composition of soil, air, and water, affecting plant and organism growth.
Regulation	Regulation is necessary.	The 4R method alone may not completely avoid pollution; production and distribution of single-use disposable products must also be regulated. The newspaper report highlights strict government actions, fines, and bans as part of this regulation.

Question 18.
Write one reason why synthetic rubber is used in the manufacture of tyres.
Answer:
Synthetic rubbers are used in the manufacture of tyres because they show less wear and tear compared to natural rubber, making them more durable.

Question 19.
Try pulling and stretching a jute rope and a rubber band with force. What happens? Why?
Answer:

Material	What Happens	Why?
Jute Rope	It will stretch very little and may snap or break if enough force is applied.	Jute is a natural fibre, and fibres are polymers that are designed to be strong with low elasticity.
Rubber Band	It stretches significantly with less force and recoils when released.	Rubber is a polymer with an inherent elastic nature.

Question 20.
Comparison of Natural and Synthetic Fibres (Completing Table 15.3)

Answer:

Characteristics	Natural Fibres	Synthetic
Air circulation	More	Fibres
Water absorption	More	Less
Durability	Lower	Less
Weight	Higher	Higher

Question 21.
What is the advantage of blending natural fibres along with synthetic fibres?
Answer:
The advantage is to overcome the limitations of both types. Blending combines the best properties of both, such as the comfort and good water absorption of natural fibres with the durability, strength, and wrinkle resistance of synthetic fibres.

Question 22.
Write down the uses of fibres.
Answer:
Apart from clothing, fibres are used for:

• Making ropes, mats, and nets.
• Making fishing nets (e.g., Nylon fibres).
• Used to prevent soil erosion and to make geotextiles for agricultural use.

Question 23.
Complete the table based on polymer characteristics (Completing Table 15.8).

Answer:

Characteristics	Polymer
Suitable for making strong threads	Nylon (or Polyester)
Polymer that can be moulded into various shapes	Plastic
Polymer with elastic nature	Rubber (Natural or Synthetic)

Textbook Page No : 254

Question 24.
List the other materials around us that are made with the help of chemistry.
Answer:

1. Dyes
2. Perfumes
3. Soaps
4. Medicines
5. Fertilizers
6. Pesticides
7. Cosmetics

Class 8 Basic Science Chapter 15 Question Answer Extended Activities

Question 1.
Organize an exhibition on the theme “The Discovery of Glass and the Growth of Science,” including descriptions and pictures of the history of glass making and different types of glasses.

Question 2.
Prepare a seminar paper on the topic “Microplastic Pollution”

Chemistry of Matter Class 8 Notes

Class 8 Basic Science Chemistry of Matter Notes Kerala Syllabus

Natural vs. Synthetic Materials
We use diverse objects made from both natural substances and synthetic materials. Material Chemistry is the branch of science that helps transform various substances into useful products for humans.

• Natural Materials: Obtained directly from nature (e.g., wood, cotton, jute).
• Synthetic Materials: Man-made materials, often produced through chemical processes (e.g., glass, plastic).

Glass
Glass is a synthetic material and an amorphous (non-crystalline) transparent substance.

Manufacturing and Composition

• Glass is formed when silicon dioxide in sand undergoes a chemical reaction with metal salts at high temperatures.
• The primary component present in all types of glass is Silica (SiO₂).
• The accidental discovery of glass is attributed to Phoenician mariners who used blocks of washing soda (Sodium carbonate) to build a hearth on a sandy bank.

□ Properties and Colouring of Glass
Common Properties of Glass:

• Transparency (സുതാര്യത)
• Brittleness (എളുപ്പത്തിൽ പൊട്ടുന്നത്)
• Hardness
• Resistance to heat (varies by type)
• Usually an electrical insulator

□ Colouring Glass:
Glasses get different colours when specific chemicals are added during the manufacturing process.

□ Chemicals and Glass Colours

Chemicals Added	Colour of the Glass Obtained
Cadmium sulphide	Yellow
Gold chloride	Ruby red
Chromium oxide	Green
Cobalt oxide	Blue

□ Types:
Different types of glass are made by varying the components added to silica.

• Soda lime glass: Bottles, window glass.
• Borosilicate glass: Lab equipment, cookware.
• Flint glass: Lenses, prisms.
• Common Component: Silica (SiO₂) is present in all types.

ഗ്ലാസ് ഒരു കൃത്രിമ പദാർത്ഥമാണ്. മണലിലെ സിലിക്കയും (SiO₂) ലോഹ ലവണങ്ങളും (metal salts) ഉയർന്ന താപനിലയിൽ പ്രവർത്തിച്ചാണ് ഗ്ലാസ് ഉണ്ടാക്കുന്നത്. വിവിധ രാസവസ്തുക്കൾ ചേർത്ത് ഗ്ലാസിന് നിറം നൽകാം.

Polymers
Many synthetic materials like plastics, rubber, and synthetic fibres belong to a group called polymers.

Polymerisation (പോളിമറൈസേഷൻ):
Polymerisation is the process in which many small molecules combine under high pressure and temperature to form large molecules.

Monomers (മോണോമറുകൾ): The small molecules used in polymerisation are called monomers.
Polymers (പോളിമറുകൾ): The large molecules formed by the combination of a large number of monomers are called polymers.

Key Points:

• The study of polymers is known as polymer chemistry.
• Hermann Staudinger is known as the Father of Polymer Chemistry.
• Bakelite is the first synthetic polymer.
• Polymers have much higher molecular mass than ordinary molecules, leading to different properties.

അനേകം ചെറിയ തന്മാത്രകൾ (മോണോമറുകൾ) ഉയർന്ന മർദ്ദത്തിലും താപനിലയിലും സംയോജി ച്ച് വലിയ തന്മാത്രകൾ (പോളിമറുകൾ) ഉണ്ടാകു ന്ന പ്രിയയാണ് പോളിമറൈസേഷൻ. പ്ലാസ്റ്റിക്, റബ്ബർ, നാരുകൾ എന്നിവയെല്ലാം പോളിമറുകൾ ക്ക് ഉദാഹരണമാണ്.

□ Classification of Polymers
Polymers can be classified in different ways:
1. Based on Physical Properties: They can be grouped into plastics, rubber, and fibres.

□ Based on Origin:
Natural Polymers: Found in nature.
Synthetic Polymers: Man-made polymers.

Natural Polymers	Synthetic Polymers
Cellulose	Polythene
Starch	Nylon
Natural rubber	Bakelite
	PVC, Synthetic rubbers

□ Common Synthetic Polymers and Their Uses

Polymer	Characteristics	Uses
Polyethylene (Polythene)	Inert nature (രാസപ്രവർത്ത നത്തിൽ ഏർപ്പെടാത്ത സ്വഭാവം)	Food containers, packaging
Polytetrafluoroethylene (PTFE / Teflon)	Heat resistance (താപം പ്രതിരോധിക്കാനുള്ള കഴിവ്)	Cookwares used at high temperatures (Non-stick)
Polyvinyl chloride (PVC)	Electrical resistance (വൈദ്യുതി പ്രതിരോധിക്കാനുള്ള കഴിവ്)	Cables, Pipes
Polyethylene terephthalate (PET)	Prevents gas permeation (വാതകങ്ങളെ കടത്തിവിടില്ല)	Used in bottle manufacturing

Plastics
Plastics are highly demanded due to their unique properties, such as being

• Can be reshaped (രൂപമാറ്റം വരുത്താം)
• Lightweight
• Durable
• Often resistant to chemicals
• Can be electrical insulators
• Can be moulded into various shapes easily

□ Classification of Plastics
Plastics can be further classified based on their behaviour when heated:
1. Thermoplastics:
These plastics can be reheated, melted, and reshaped into new products multiple times. They soften on heating and harden on cooling.
Example: The plastic carry bags we use (Polythene), PVC pipes.

2. Thermosetting Plastics:
These plastics cannot be reheated and melted to reshape them once they have been set. They undergo a permanent chemical change during moulding.
Example: Items like the handle of a pressure cooker (e.g., Bakelite).
ചൂടാക്കുമ്പോൾ മൃദുവാകുകയും തണുപ്പിക്കു മ്പോൾ ഉറയ്ക്കുകയും ചെയ്യുന്ന പ്ലാസ്റ്റിക്കുകളാണ് തെർമോപ്ലാസ്റ്റിക്കുകൾ. ഇവയെ വീണ്ടും ചൂടാക്കി രൂപമാറ്റം വരുത്താൻ കഴിയും. എന്നാൽ, നിർമ്മാ ണ വേളയിൽ ചൂടാക്കുമ്പോൾ ഉറയ്ക്കുകയും, പി ന്നീട് ചൂടാക്കിയാൽ മൃദുവാകാത്തതുമായ പ്ലാസ്റ്റി ക്കുകളാണ് തെർമോസെറ്റിംഗ് പ്ലാസ്റ്റിക്കുകൾ. ഇ വയെ വീണ്ടും രൂപമാറ്റം വരുത്താൻ സാധ്യമല്ല.

□ Identifying Different Types of Plastics
Different types of plastics have specific properties and recycling potential. They are often identified using Resin Identification Codes (the number inside the chasing arrows symbol).

Plastic Pollution ((പ്ലാസ്റ്റിക് മലിനീകരണം)
While plastics have many benefits, their uncontrolled use leads to significant environmental problems.

• Problem: Plastics accumulate in the environment, causing water and soil pollution. They alter the natural composition of soil, air, and water, affecting the growth of plants and soil organisms.
• Solution (The 4R Approach): To reduce plastic pollution, the 4R approach is recommended:
  • Refuse (ഒഴിവാക്കുക): Avoid giving or accepting plastic products whenever possible.
  • Reduce (ഉപയോഗം കുറയ്ക്കുക): Minimise the use of plastic products.
  • Reuse (പുനരുപയോഗിക്കുക): Reuse plastic products multiple times.
  • Recycle (പുനഃചംക്രമണം ചെയ്യുക): Convert plastic products into new items through physical and chemical processes.
• Regulation: Governments are also taking action by banning certain single-use plastics and imposing fines for littering.

Rubbers (റബ്ബറുകൾ)
Rubbers are polymers known for their elastic nature.

• Natural Rubber:
  • An elastic natural polymer.
  • Obtained from the latex collected from the rubber tree.
• Synthetic Rubber:
  • Produced to meet increased demand and overcome limitations of natural rubber.
  • Shows less wear and tear compared to natural rubber.
  • Use: Widely used in the manufacture of tyres.

Fibres (നാരുകൾ)

• Fibres are polymers that are strong and long.
• For a polymer to be considered a fibre, its length must be at least a hundred times its diameter.
• Uses: Apart from clothing, fibres are used to make ropes, mats, nets, geotextiles, etc..
• Synthetic Fibres:
  • Developed to overcome the limited availability and quality issues of natural fibres.
  • Nylon is the first synthetic fibre made by humans.
• Blending Fibres: To overcome the limitations of both types, natural fibres are often blended with synthetic fibres.