Term 3 · Class 7 Science · Chapter 3

Samacheer Class 7 Science - Polymer Chemistry

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Chapter-wise textbook exercise answers for Polymer Chemistry with validation-aware solutions.

Answers marked verified were checked during generation against the chapter context and source question text.
Sections in this chapter
I. Choose the correct answers : 7II. Fill in the blanks : 1III. True or False : 5IV. Match the following : 1V. Arrange in Correct Sequence: 1VI. Analogy : 2VII. Assertion – Reason type question : 3IX. Very short answer : 6X. Short Answer : 3XI. Long Answer : 2XII. HOTS : 3Activity – 2 4Activity – 4 1Activity – 5 2Activity – 6 3Activity – 7 1Activity – 8 1
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1I. Choose the correct answers :7 questions
Q.1The first man-made fibre is ________v
  1. A. Nylon
  2. B. Polyester
  3. C. Rayon
  4. D. Cotton
Answer:

(c) Rayon

Q.2Which of the following is the strongest?v
  1. A. Rayon
  2. B. Nylon
  3. C. Acrylic
  4. D. Polyester
Answer:

(b) Nylon

Q.3When you place a natural fibre in a flame it ________v
  1. A. melts
  2. B. burns
  3. C. gets nothing
  4. D. explodes
Answer:

(b) burns

Q.4A synthetic fibre which has similar properties to wool is ________v
  1. A. Nylon
  2. B. Polyester
  3. C. Acrylic
  4. D. PVC
Answer:

(c) Acrylic

Q.5A good application of plastic is the use of ________v
  1. A. Blood bags
  2. B. Plastic cutlery
  3. C. Plastic straws
  4. D. Plastic carry bag
Answer:

(a) Blood bags

Q.6________ is non-biodegradable material.v
  1. A. Paper
  2. B. A plastic bottle
  3. C. Cotton cloth
  4. D. Wool
Answer:

(d) Wool

Q.7PET is the acronym for ________v
  1. A. Polyester
  2. B. Polyester and terylene
  3. C. Polyethylene terephthalate
  4. D. Polyetheneterylene
Answer:

(c) Polyethylene terephthalate

2II. Fill in the blanks :1 questions
Q.G1______ 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 fibreis called ______ A natural fibre obtained by boiling of cocoons is called ______v
Answer:

Raincoat
Resin codes
polymer
plant fibre
silk

3III. True or False :5 questions
Q.1A lot of plastic pollutes our environment.v
Answer:

True. Plastic pollution is a significant environmental problem because plastics are synthetic materials that do not decompose naturally for hundreds of years. When plastic waste is discarded, it accumulates in landfills, oceans, and natural environments, causing harm to wildlife and ecosystems. Plastic particles break down into microplastics that enter food chains and water systems, affecting both animals and humans. The production of plastics also consumes fossil fuels and generates greenhouse gases, contributing to climate change.

Q.2Refuse (avoid) is the best way to manage plastic.v
Answer:

True. Refusing to use plastic, or avoiding plastic consumption, is considered the most effective strategy in plastic waste management. This approach is at the top of the waste management hierarchy because it prevents plastic from being produced and used in the first place, eliminating the problem at its source. By refusing single-use plastics such as bags, straws, and packaging, individuals can significantly reduce the amount of plastic waste entering the environment. This is more effective than recycling or reusing plastics because it avoids the energy and resources required for processing and transportation.

Q.3It is good to wear clothes made of synthetic fibres while cooking.v
Answer:

False. It is not good to wear clothes made of synthetic fibres while cooking. Correct statement: It is good to wear clothes made of natural fibres such as cotton while cooking. Synthetic fibres like polyester and nylon have low melting points and can easily catch fire or melt when exposed to heat from cooking stoves or flames. Natural fibres like cotton have higher melting points and are safer to wear in the kitchen. Additionally, natural fibres are more breathable and comfortable in hot environments.

Q.4Degradable plastics break down into tiny pieces called microplastics.v
Answer:

True.

Q.5Cotton is a natural polymer.v
Answer:

True.

4IV. Match the following :1 questions
Q.G2A B 1. Nylon Thermoplastic 2. PVC Thermosetting plastic 3. Bakelite Fibre 4. Teflon Wood pulp 5. Rayon Non-stick cookwaresv
Answer:

A
B
1. Nylon
Fibre
2. PVC
Thermoplastic
3. Bakelite
Thermosetting plastic
4. Teflon
Non-stick cookwares
5. Rayon
Wood pulp

5V. Arrange in Correct Sequence:1 questions
Q.G31. Mix water, starch, vinegar and glycerin in a cooking pot. 2. Let the article cool for 24 hours before we use it. 3. Shape 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 aluminium foil and cool.v
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.

6VI. Analogy :2 questions
Q.2PLA spoon :compostable:: Plastic spoon: ______v
Answer:

Disposable.

Q.3Nylon :melts on heating:: Silk: ______v
Answer:

Burns on heating.

7VII. Assertion – Reason type question :3 questions
Q.1Assertion (A) : Vegetable peels buried in the soil disappear within two weeks. Reason (R) : Vegetable peels are compostable.v
Answer:

(a) Both A and R are true and R is the correct explanation of A

Q.2Assertion (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.v
Answer:

(a) Both A and R are true and R is the correct explanation of A

Q.3Assertion (A) : It is good to avoid plastics. Reason (R) : Plastics end up polluting the environment.v
Answer:

(a) Both A and R are true and R is the correct explanation of A

8IX. Very short answer :6 questions
Q.1What is the chemical name of the polymers that make up cotton?v
Answer:

The chemical name of the polymer that makes up cotton is cellulose. Cellulose is a natural polysaccharide composed of long chains of glucose units linked together. It is the primary structural component of plant cell walls and is the most abundant organic polymer found in nature, making it an ideal material for producing natural fibres and textiles.

Q.2What gives plastic different qualities and characteristics?v
Answer:

Different chemicals called additives are added to plastic to give them various qualities and characteristics. These additives can include plasticizers to increase flexibility, stabilizers to prevent degradation, colorants for pigmentation, flame retardants for fire resistance, and other compounds that modify properties such as hardness, transparency, durability, and resistance to heat or chemicals, allowing plastics to be customized for specific applications.

Q.3It is not advisable to burn plastic and synthetic fabrics. Why?v
Answer:

Burning of plastics and synthetic fabrics is not a good solution, as we end up wasting non-renewable resources and produce super toxic chemicals that are difficult to store or dispose safely.

Q.4A bucket made of plastic does not rust like a bucket made of iron. Why?v
Answer:

The reason is due to their chemical composition.
The bucket is made of plastic which does not react with the oxygen and humidity present in air.
While the iron reacts with the oxygen, air corrodes to form rust.

Q.5Why is it better to avoid the use of plastic products?v
Answer:

It is better to avoid the use of plastic products for several important reasons. Plastics do not decompose through natural processes and the action of bacteria, making them non-biodegradable and persistent in the environment for hundreds of years. Most plastic produced globally is designed for single-use and is discarded after brief use, creating enormous amounts of plastic waste. This waste ends up being recycled, incinerated, landfilled, dumped in oceans, or littering our environment as pollution. Plastic waste harms wildlife, contaminates soil and water, breaks down into microplastics that enter food chains, and depletes non-renewable fossil fuel resources used in plastic production. Therefore, reducing plastic consumption and choosing biodegradable alternatives is essential for environmental protection and sustainability.

Q.6Give two examples of thermosetting plastics.v
Answer:

Bakelite, Melamine.

9X. Short Answer :3 questions
Q.1What does the term biodegradable mean?v
Answer:

A material that gets decomposed through natural processes and the action of bacteria is called biodegradable. Biodegradable materials break down into simpler substances like water, carbon dioxide, and organic matter that can be safely absorbed back into the environment without causing pollution. Examples include paper, cotton, food waste, and certain plastics made from plant-based materials, which decompose naturally within a reasonable time period.

Q.2What kind of fabric is suitable to dress-up and play in summer? Why?v
Answer:

In summer it is better to wear clothing made from cotton materials rather than synthetic fabrics. Cotton is suitable for summer wear because it is a natural fibre that absorbs moisture effectively, allowing sweat to evaporate from the skin and keeping the body cool and comfortable. Cotton also allows good air circulation through the fabric, which helps maintain body temperature. In contrast, most synthetic fibres such as polyester and nylon absorb very little moisture and do not allow adequate air circulation, causing sweat to accumulate on the skin and making the clothing feel hot, sticky, and uncomfortable during hot and humid summer weather.

Q.3How do plastics impact animals and the environment?v
Answer:

The increase in the use of plastics, particularly one-time use and throw away plastics, has serious impacts on the environment, animals, and our health. One major problem with plastics is that they do not decompose or biodegrade easily. This leads to large amounts of waste that will not disappear and end up accumulating in landfills, oceans, and natural habitats, causing severe pollution. Many animals confuse plastic for food and eat it accidentally. When leftover food is thrown away packed in plastic, animals smell the food inside and consume the plastic along with it, which can cause injury, blockage in their digestive systems, or even death. Plastic waste in oceans harms marine life such as fish, turtles, and birds that mistake plastic bags and other debris for food. Additionally, plastics break down into microplastics over time, which enter the food chain and can affect both wildlife and human health. The persistence of plastic waste in the environment means that plastics discarded today will remain as pollution for hundreds of years, making it a critical environmental concern that requires urgent action and reduction in plastic consumption.

10XI. Long Answer :2 questions
Q.1List the advantages and disadvantages of synthetic fibres.v
Answer:

Advantages-and disadvantages of synthetic fibres.
Advantages of synthetic fibres
Disadvantages of synthetic fibres
1.
Do not wrinkle easily and they keep their colour and brightness for a much longer time than natural fibres such as cotton.
synthetic fibres such as polyester is that they are not heat resistant and catch fire easily.
2.
Using synthetic fibres such as nylon, is that they are stronger than many natural fibres such as silk or wool.
Most synthetic fibres absorb very little moisture and do not allow air circulation making them hot and uncomfortable to wear.
3.
These fibres are strong and elastic which gives it the properties to bounce.
Synthetic fibres are made out of petrochemicals and last in the environment for a very long time. It break down into very small pieces called microplastics which cause pollution to soil and water bodies such as rivers, lakes and oceans.

Q.2Suggest safe methods of disposing plastics.v
Answer:

Refuse (Avoid):
The best thing to do is to avoid using plastic products.
One-time use throw away plastics can often be avoided.
Reduce : Reducing the amount of plastic we use is important.
Reuse : If possible products made of plastics can be used again and again.
Recycle:
It is better to recycle plastic waste.
Separating plastic waste (based on the resin code) and making sure it gets recycled is good as it turns waste materials into something new.
Then it will not be thrown away in landfills, open dumps or ending up as litter in the environment.
Solid waste can be converted into resources such as electricity and compost through thermal and biological means.

11XII. HOTS :3 questions
Q.1The Tamil Nadu Government has banned the use of one-time use throw away plastics. Why do you think this is important?v
Answer:

The Tamil Nadu Government's ban on one-time use throw away plastics is important because it helps reduce the accumulation of plastic waste in the environment. Single-use plastics such as bags, bottles, and packaging materials are used for only a few minutes but persist in nature for hundreds of years, causing severe environmental pollution. By banning these plastics, the government aims to decrease the amount of non-biodegradable waste that ends up in landfills and oceans, protecting wildlife from ingesting plastic and suffering harm. This ban encourages people to use alternative materials like cloth bags and paper products, promoting sustainable practices and reducing the negative consequences of plastics on ecosystems, animals, and human health.

Q.2A plastic bag dumped in the soil stays without breaking down for 500years. If a new generation starts in every 30 years, how many generations would it take to see the plastic bag finally broken down?v
Answer:

It would take 16 to 17 generations to see the plastic bag finally broken down.
XIII.

Q.3Read the following information and convert them into a graph to compare the countries and the amount of plastic they use. China contributes the highest share – that is around 28%, of the total plastic used globally. Indonesia uses 10%, both the Philippines and Vietnam use 6% each; Thailand uses 3.2%, Egypt 3%, Nigeria 2.7% and South Africa 2%.v
Answer:

12Activity – 24 questions
Q.1Arrange the threads in the order of increasing strength.v
Answer:

The threads arranged in the order of increasing strength are: Cotton, Wool, Silk, Nylon. Cotton is the weakest among these fibres, followed by wool which is stronger than cotton. Silk is stronger than wool, and nylon is the strongest of all these fibres. This arrangement reflects the structural properties of each fibre, with natural fibres like cotton and wool being relatively weaker, while synthetic fibres like nylon possess greater tensile strength due to their chemical composition and manufacturing process.

Q.2What do you infer from the above activity?v
Answer:

From the above activity, we can infer that synthetic fibres are stronger than natural fibres. Nylon, which is a synthetic fibre, demonstrates the greatest strength compared to natural fibres like cotton, wool, and silk. This shows that synthetic fibres have superior tensile strength and durability, making them more suitable for applications requiring high strength and resistance to tearing or breaking. The comparison reveals that the manufacturing process of synthetic fibres produces materials with better mechanical properties than naturally occurring fibres.

Q.3Which type of fibre is the strongest?v
Answer:

Nylon is the strongest type of fibre. It is a synthetic fibre that possesses superior tensile strength compared to natural fibres such as cotton, wool, and silk. Due to its high strength and durability, nylon is widely used in various applications including clothing, ropes, fishing nets, parachutes, and industrial materials where resistance to tearing and breaking is essential.

Q.4Which type of fibre is the weakest?v
Answer:

Cotton is the weakest type of fibre among commonly used natural and synthetic fibres. It has lower tensile strength compared to wool, silk, and synthetic fibres like nylon and polyester. Despite being weaker in strength, cotton is widely used in textiles because of its other desirable properties such as comfort, breathability, and ability to absorb moisture, making it suitable for clothing and everyday fabrics.

13Activity – 41 questions
Q.1Synthetic or Natural Fibres : The teacher can give the learner a piece of each and every type of fibre. The learner can feel the fibre and write down the name of the fibre and state whether it is natural or synthetic fibre.v
Answer:

Natural and synthetic fibres can be identified and classified based on their origin and properties. Jute is a natural fibre obtained from plants and is used for making ropes and bags. Cotton is a natural fibre derived from cotton plants and is widely used in textiles for clothing. Rayon is a synthetic fibre manufactured from cellulose and is used as an alternative to natural fibres in fabrics. Wool is a natural fibre obtained from sheep and other animals, known for its warmth and insulation properties. Polyester is a synthetic fibre created through chemical processes and is used in various applications due to its durability and water-resistant properties. Natural fibres come from plants and animals, while synthetic fibres are manufactured through chemical processes in industries. Each type of fibre has distinct characteristics that make it suitable for different purposes in textiles and other applications.

14Activity – 52 questions
Q.1What do you observe while the cotton cloth burns?v
Answer:

When cotton cloth burns, it burns completely without melting. The burning process produces an odour similar to burning paper, which is characteristic of natural cellulose fibres. Cotton does not melt because it is a natural fibre made of cellulose, which decomposes at high temperatures rather than melting into a liquid form like synthetic fibres do.

Q.2What do you observe while the polyester cloth burns?v
Answer:

When polyester cloth burns, it melts on burning and produces black smoke. This melting behaviour is characteristic of synthetic fibres, which have a lower melting point compared to natural fibres. The black smoke indicates the release of carbon and other combustion products from the synthetic polymer chains, showing that polyester undergoes thermal decomposition and melting rather than simple burning like natural fibres.

15Activity – 63 questions
Q.1We use an umbrella on rainy days. What kind of umbrella do we use?v
Answer:

On rainy days, we use umbrellas made of nylon or polyester fabric. These synthetic materials are preferred for umbrellas because they are water-resistant and do not allow water to pass through easily. Both nylon and polyester have properties that make them ideal for protecting against rain, as they repel water and dry quickly after use.

Q.2Which of these fabrics allows water to pass through?v
Answer:

Cotton cloth allows water to pass through it because it is a natural, absorbent fibre that readily absorbs moisture. In contrast, umbrella cloth, which is typically made of synthetic materials like nylon or polyester, does not allow water to pass through because these synthetic fibres are water-resistant and have a tightly woven structure that prevents water penetration. This difference in water permeability makes cotton suitable for everyday clothing while synthetic fabrics are ideal for rain protection.

Q.3Which of these fabrics dries the fastest? The cotton cloth or the umbrella cloth?v
Answer:

Umbrella cloth dries the fastest compared to cotton cloth. This is because umbrella cloth, made of synthetic fibres like nylon or polyester, does not absorb water and allows it to remain on the surface where it can evaporate quickly. Cotton cloth, being a natural and absorbent fibre, absorbs water into its structure, which takes longer to dry as the water must evaporate from within the fabric. The water-resistant nature of synthetic umbrella fabric enables faster drying compared to the water-absorbing properties of cotton.

16Activity – 71 questions
Q.1Right and wrong application of plastics. Look at the list of eight plastic items. Decide which four plastic items are used for the right application and which four are used for the wrong application by filling in the chart below: Plastic items: straws, helmets, cutlery, thin carry bags, syringes, electrical wires,tea cups and blood bags v
Answer:

Right application of plastics: Helmets are made from strong, rigid plastics that provide protection and durability needed for safety. Syringes are made from sterilizable plastics that are safe for medical use and can be easily disinfected. Electrical wires are insulated with plastics because they are excellent insulators and prevent electric shock. Blood bags are made from plastics that are sterile, safe for storing blood, and do not react with blood. Wrong application of plastics: Straws are single-use items made from plastics that contribute to pollution and are not necessary for daily function. Thin carry bags are made from non-biodegradable plastics that cause severe environmental pollution and harm to wildlife. Cutlery made from plastics is unnecessary when durable alternatives exist and contributes to plastic waste. Tea cups made from plastics are not ideal because they can leach harmful chemicals when hot liquids are poured into them.

17Activity – 81 questions
Q.1Identify the different types of plastics. Collect different kinds of plastic products and look carefully for the resin code and/or acronym on them. With the help of the resin code chart, mark the resin code number, acronym, if you think it is a safer, unsafe or questionable (when you cannot find the resin code in the article) type of plastic. What resin codes do you find? Is the resin code safer, un safe or questionable?v
Answer:

Product
Resin code number
Acronym
Category of safety
Use of product
Rain coat
03
PVC
Unsafe
During rain
Pens
06
PS
Unsafe
To write