RBSE Solutions Class 12 Chemistry Chapter 15 Polymers

RBSE Class 12 Chemistry Chapter 15 Text Book Questions

RBSE Class 12 Chemistry Chapter 15 Multiple Choice Questions

 

Question 1. Which of the following is not true about polymers?
(a) Polymers have low molecular weight.
(b) Polymers have no charge.
(c) Polymers have high viscosity.
(d) Polymers scatter light.
Answer: (a) Polymers have low molecular weight.
In simple words: Polymers are actually very large molecules made of many small units, so they have a high molecular weight. Therefore, stating they have a low molecular weight is not true.

🎯 Exam Tip: Remember that polymers are macro-molecules, which means they are characterized by their very high molecular mass, not low.

 

Question 2. On the basis of the method of polymerisation, polymers are classified as:
(a) Copolymer
(b) Homopolymer
(c) Monomer
(d) Condensation polymer
Answer: (c) Monomer
In simple words: Monomers are the small, individual building blocks that join together to form a polymer. They are not a classification of polymers themselves based on the method of polymerization.

🎯 Exam Tip: Understand the difference between a monomer (the basic unit) and a polymer (the large chain) and how polymers are classified by their formation methods (addition, condensation) or structure (homo-, co-polymer).

 

Question 4. Which of the following is condensation polymer?
(a) Dacron
(b) Teflon
(c) PVC
(d) Polythene
Answer: (a) Dacron
In simple words: Dacron is a type of polyester, which is created through a condensation reaction where small molecules, like water, are removed when the monomers join.

🎯 Exam Tip: Condensation polymers are formed by reactions that eliminate small molecules, such as water or methanol, as the monomers link together.

 

Question 5. Which of the following is not a true polymer?
(a) Ethene
(b) Styrene
(c) Isoprene
(d) Butadiene
Answer: (c) Isoprene
In simple words: Isoprene, like the other options, is a monomer, which is a small molecule that serves as a building block. It is not a large polymer molecule itself. Isoprene is known as 2-methyl-1,3-butadiene, and it's the monomer for natural rubber.

🎯 Exam Tip: Remember that "not a true polymer" usually refers to a monomer, which is the basic unit that polymerizes to form a polymer.

 

Question 6. Which of the following has a ester bond?
(a) Nylon
(b) Bakelite
(c) Terylene
(d) Rubber
Answer: (c) Terylene
In simple words: Terylene, which is a type of polyester, gets its name because its monomer units are joined together by special chemical links called ester bonds.

🎯 Exam Tip: Polymers like Terylene (polyesters) are characterized by the presence of ester linkages in their repeating units.

 

Question 7. Terylene is a condensation polymer of ethylene glycol and:
(a) Terephthalic acid
(b) Phthalic acid
(c) Benzoic acid
(d) Acetic acid
Answer: (a) Terephthalic acid
In simple words: Terylene is formed when ethylene glycol and terephthalic acid react together, joining into long chains and releasing water molecules in the process.

🎯 Exam Tip: Knowing the specific monomers for common polymers like Terylene is essential, especially for condensation polymers where two different monomers combine.

 

Question 9. Teflon is a polymer of:
(a) Tetrafluoroethylene
(b) Tetraiodoethylene
(c) Tetrachloroethylene
(d) Tetrabromoethylene
Answer: (a) Tetrafluoroethylene
In simple words: Teflon is a well-known polymer made by linking many units of tetrafluoroethylene together, giving it properties like non-stickiness and resistance to heat.

🎯 Exam Tip: Connect the name of the polymer (Teflon) with its monomer (Tetrafluoroethylene) and understand the role of fluorine atoms in its properties.

 

Question 10. Which of the following is a bio-degradable polymer?
(a) PVC
(b) Cellulose
(c) Polythene
(d) Nylon - 6
Answer: (b) Cellulose
In simple words: Cellulose is a natural polymer, found in plant cell walls, that can be broken down by living organisms, meaning it is biodegradable and can return to nature.

🎯 Exam Tip: Biodegradable polymers are often natural polymers or specially designed synthetic ones that can decompose in the environment, reducing pollution.

RBSE Class 12 Chemistry Chapter 15 Very Short Answer Type Questions

 

Question 1. Define polymers?
Answer: Polymers are large chemical substances with very high molecular weight, typically ranging from \(10^3\) to \(10^7\) atomic mass units. They are made up of many small, repeating units called monomers joined together. This repeating structure gives polymers their unique properties.
In simple words: Polymers are big molecules made from many small, identical building blocks linked together.

🎯 Exam Tip: When defining polymers, mention both "high molecular mass" and "repeating structural units" (monomers).

 

Question 2. Give two examples of natural and synthetic polymers along with their structures.
Answer:Natural polymers are found in nature, like natural rubber. Natural rubber is a polymer of isoprene units. Synthetic polymers are man-made, such as Nylon 6,6. Nylon 6,6 is created by joining together two different types of small molecules: hexamethylenediamine and adipic acid. Understanding the monomer units helps explain the polymer's overall properties.
In simple words: Natural polymers are like rubber that comes from trees. Synthetic polymers are man-made, like Nylon 6,6.

🎯 Exam Tip: When giving examples, it's good to briefly mention the monomer units for each polymer if known, especially for synthetic ones like Nylon 6,6.

 

Question 3. Give one difference between homopolymer and copolymer.
Answer:A **homopolymer** is a type of polymer that is made from only one kind of repeating building block, or monomer. For instance, PVC (polyvinyl chloride) is a homopolymer because it is made entirely from vinyl chloride monomers. In contrast, a **copolymer** is a polymer formed from two or more different types of monomer units. An example of a copolymer is one made from 1,3-butadiene and styrene, which creates a mixed polymer with combined properties.
In simple words: Homopolymers use only one type of building block, like a wall made of only red bricks. Copolymers use two or more different types of building blocks, like a wall made of red and blue bricks.

🎯 Exam Tip: Remember to provide a clear example for both types of polymers to illustrate the difference effectively.

 

Question 4. How many methods of chain termination are there in the free radical mechanism?
Answer: There are three main ways a free radical polymer chain reaction finishes or ends its growth, according to these classifications. These methods are: chain initiating, which is the very beginning of the reaction; chain propagation, where the chain grows; and chain termination, which marks the end of the polymer growth. An important part of polymerization is understanding how these steps manage the overall process.
In simple words: A polymer chain reaction has three general stages: chain starting, chain growing, and chain stopping.

🎯 Exam Tip: For questions about reaction mechanisms, it is important to clearly list and distinguish all the different stages involved.

 

Question 5. Which monomers are polymerised by cationic polymerisation?
Answer: Monomers that are polymerised through cationic polymerization are typically vinyl derivatives. These are molecules with a carbon-carbon double bond, often with electron-donating groups attached, which helps stabilize the positively charged intermediate. This stabilization is key for the reaction to proceed efficiently.
In simple words: Cationic polymerization uses monomers that have a special vinyl group, but with added parts that make them more positive, helping the reaction happen.

🎯 Exam Tip: Remember that cationic polymerization favors monomers with electron-donating groups, which stabilize the carbocation intermediate.

 

Question 7. Give the name of substances used in the vulcanisation of rubber.
Answer: The primary substance used in the vulcanization of rubber is sulfur (S). This process makes rubber stronger and more elastic by forming cross-links between the polymer chains, significantly improving its durability and elasticity.
In simple words: Sulfur is used to make rubber stronger and more stretchy, in a process called vulcanization.

🎯 Exam Tip: Sulfur is the key agent for vulcanization, improving rubber's durability and elasticity.

 

Question 8. Write the name of the monomer of neoprene.
Answer: The monomer unit for neoprene is 2-chlorobut-1,3-diene. This specific diene molecule has a chlorine atom at the second carbon position, which influences the properties of the resulting synthetic rubber. The structure of 2-chlorobut-1,3-diene is \( \text{CH}_2 = \text{C(Cl)-CH} = \text{CH}_2 \).
In simple words: Neoprene is made from a small molecule called 2-chlorobut-1,3-diene.

🎯 Exam Tip: Always provide the full chemical name and, if possible, the basic structure for monomers when asked.

 

Question 9. Write the chemical formula of Nylon – 6, 6.
Answer: Nylon 6,6 is a polyamide polymer. Its chemical formula represents the repeating unit formed from two monomers: hexamethylenediamine and adipic acid. The structure includes repeating amide bonds \( \text{(-NH-CO-)} \) and methylene chains. This specific combination gives Nylon 6,6 its strength and durability. The repeating unit is \( \text{-(NH-(CH}_2\text{)}_6\text{-NH-CO-(CH}_2\text{)}_4\text{-CO)-}_n \).
In simple words: Nylon 6,6 is a strong plastic made by joining two specific chemicals, hexamethylenediamine and adipic acid, over and over again.

🎯 Exam Tip: For condensation polymers like Nylon 6,6, identifying the two different monomers and the type of bond formed (amide in this case) is crucial.

 

Question 10. Give two examples of synthetic biopolymers.
Answer: Two examples of synthetic biopolymers are PHBV (Poly \(\beta\)-hydroxybutyrate-co-\(\beta\)-hydroxyvalerate) and Nylon-2,6. These materials are man-made but designed to be biodegradable, making them more environmentally friendly than traditional plastics by allowing them to break down in nature.
In simple words: Two examples of man-made, eco-friendly plastics that can break down naturally are PHBV and Nylon-2,6.

🎯 Exam Tip: When giving examples of biopolymers, try to include one that is explicitly a copolymer like PHBV, as it shows complexity.

RBSE Class 12 Chemistry Chapter 15 Short Answer Type Questions

 

Question 1. On the basis of the source of how polymers are classified? Give one example of each?
Answer: Based on their origin, polymers are categorized into two main types: 1. **Natural polymers:** These are polymers that exist naturally in living organisms. Examples include starch, cellulose, and proteins. These substances play vital roles in biological systems. 2. **Synthetic polymers:** These are man-made polymers, created through chemical reactions in laboratories or industries. An example is polyethylene, widely used in plastics.
In simple words: Polymers are grouped by where they come from: natural ones found in plants and animals (like starch) and synthetic ones made by people (like plastic).

🎯 Exam Tip: When classifying by source, clearly state "Natural" and "Synthetic" polymers, and provide a common example for each.

 

Question 2. Differentiate between thermoplastic and thermosetting polymers.
Answer:**Thermoplastic polymers** are long chain molecules that can be heated, softened, and reshaped multiple times, and then they harden again when cooled. Their internal forces are stronger than in rubber but weaker than in fibers. Common examples include polythene and polystyrene. These can be recycled easily. **Thermosetting polymers** are very branched or cross-linked molecules. Once they are heated and shaped, they become hard and cannot be softened or reshaped again. They are often used in molds because of their permanent structure. Bakelite and urea-formaldehyde resins are good examples of thermosetting polymers.
In simple words: Thermoplastics can be melted and reshaped again and again, like plastic bottles. Thermosetting plastics get hard once heated and shaped, and cannot be melted again, like car tires.

🎯 Exam Tip: The key difference is recyclability and softening upon heating; thermoplastics soften, thermosets do not.

 

Question 3. In free radical polymerisation, where do we use hydroquinone? Explain.
Answer: In free radical polymerization, hydroquinone is used as an inhibitor to prevent or slow down the reaction. It works because hydroquinone converts into benzoquinone, which then reacts with a free radical intermediate. This reaction forms a new radical that is very stable due to resonance, making it non-reactive and stopping the polymerization chain. This helps control the reaction rate or stops it completely, preventing unwanted side reactions.
In simple words: Hydroquinone stops or slows down free radical reactions. It turns into benzoquinone, which traps the active radicals and makes them stable, so the reaction cannot continue.

🎯 Exam Tip: Hydroquinone acts as an inhibitor by forming stable, non-reactive radicals, effectively terminating the chain reaction.

 

Question 4. Give the monomer of dacron and process of polymerisation of dacron.
Answer: Dacron, also known as Terylene, is formed from two main monomers: ethylene glycol and terephthalic acid. Its polymerization is a condensation reaction, where these monomers join together by removing small molecules like water. The process is usually carried out at high temperatures, between 420 and 460 Kelvin, and uses catalysts such as zinc acetate and antimony trioxide to speed up the reaction. This precise control forms long polyester chains.
In simple words: Dacron is made from ethylene glycol and terephthalic acid. They join together at high heat with special chemicals to form long chains, letting out water as they combine.

🎯 Exam Tip: For Dacron, remember it's a condensation polymer involving ethylene glycol and terephthalic acid, and the reaction requires specific catalysts and high temperatures.

 

Question 5. What is the polydispersity index? Explain.
Answer: The polydispersity index (PDI) is a measure used to understand how uniform a polymer sample is in terms of its molecular mass. It is calculated by dividing the mass average molecular mass (\(M_w\)) by the number average molecular mass (\(M_n\)). A PDI value close to 1 means the polymer chains are very similar in length, making the sample more homogeneous. The formula for PDI is given by: \( \text{PDI} = \frac{M_w}{M_n} \). For natural polymers, the PDI is typically equal to one, which means all their molecules are nearly the same size, making them very uniform.
In simple words: Polydispersity index (PDI) tells us how much the molecules in a polymer sample differ in size. If PDI is 1, all molecules are almost the same size; if it's higher, they have many different sizes.

🎯 Exam Tip: Always state the definition of PDI, the formula \( \text{PDI} = M_w / M_n \), and the implication of a PDI value equal to 1 (monodisperse, homogeneous).

RBSE Class 12 Chemistry Chapter 15 Long Answer Type Questions

 

Question 1. Classify polymers on the following basis: (i) On the basis of monomer units. (ii) Type of polymerisation. (iii) Molecular forces.
Answer:Polymers are classified in several ways: (i) **Based on Monomer Units:** 1. **Homopolymers:** These are made from only one type of repeating building block (monomer). Examples include polythene and PVC. 2. **Copolymers:** These are made from two or more different types of monomer units. An example is Buna-S rubber, which is formed from 1,3-butadiene and styrene. (ii) **Based on Type of Polymerisation (Carothers' classification):** 1. **Addition Polymers:** These form when monomer molecules directly add to each other, usually across double or triple bonds, without losing any small molecules. PVC, Teflon, and Neoprene are examples. 2. **Condensation Polymers:** These form when monomers react to join together, and small molecules like water or ammonia are removed during the process. Bakelite and Nylon-6,6 are examples. (iii) **Based on Molecular Forces:** 1. **Elastomers:** These polymers have weak forces between chains, allowing them to stretch and return to their original shape, like vulcanized rubber. 2. **Fibres:** These have very strong forces between chains, making them tough and thread-like, such as nylon and polyesters. 3. **Thermoplastics:** These have moderate forces and can be softened by heating and reshaped, like polypropylene and polythene. 4. **Thermosetting Polymers:** These have strong, permanent cross-links that make them rigid once formed, and they cannot be melted or reshaped, like Bakelite resins. This comprehensive classification helps us understand the structure and behavior of various polymeric materials.
In simple words: Polymers are sorted by their building blocks (one type or many), how they are made (just adding on, or adding and losing small parts), and how strong the forces are between their chains (stretchy, strong threads, meltable, or solid forever).

🎯 Exam Tip: For comprehensive classification, structure your answer clearly with sub-headings for each basis and provide a relevant example for every type.

 

Question 2. What is an addition polymerisation? Explain free radical addition polymerisation mechanism by taking an example.
Answer:**Addition polymerization** is a process where many small monomer molecules, which usually have double or triple bonds, directly join together to form a larger polymer molecule without any atoms being lost. The **free radical addition polymerization mechanism** involves three main steps, using ethene as an example: 1. **Initiating Step:** This starts the reaction. An initiator, like benzoyl peroxide, breaks apart to form free radicals (like phenyl radicals). These radicals then attack an ethene monomer, creating a new, larger radical. This step is crucial for beginning the chain growth.
\( \text{C}_6\text{H}_5\text{COO-OOC-C}_6\text{H}_5 \rightarrow 2\text{C}_6\text{H}_5\cdot \) (Phenyl radical)
\( \text{C}_6\text{H}_5\cdot + \text{CH}_2 = \text{CH}_2 \rightarrow \text{C}_6\text{H}_5\text{-CH}_2\text{-CH}_2\cdot \) 2. **Chain Propagating Step:** The newly formed radical reacts with more ethene monomers, making the polymer chain grow longer and longer by continuously adding more units. This is the main growth phase.
\( \text{C}_6\text{H}_5\text{-CH}_2\text{-CH}_2\cdot + \text{CH}_2 = \text{CH}_2 \rightarrow \text{C}_6\text{H}_5\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\cdot \)
This process repeats to form \( \text{C}_6\text{H}_5\text{-(CH}_2\text{-CH}_2\text{)-}_n\text{-CH}_2\text{-CH}_2\cdot \) 3. **Chain Terminating Step:** The growing polymer chains eventually stop when two radicals combine or when a radical reacts in a way that creates stable products without any more free radicals. For instance, two growing chains can join together, bringing the polymerization to a halt.
\( \text{C}_6\text{H}_5\text{-(CH}_2\text{-CH}_2\text{)-}_n\text{-CH}_2\text{-CH}_2\cdot + \text{C}_6\text{H}_5\text{-(CH}_2\text{-CH}_2\text{)-}_n\text{-CH}_2\text{-CH}_2\cdot \)
\( \implies \text{C}_6\text{H}_5\text{-(CH}_2\text{-CH}_2\text{)-}_n\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-(CH}_2\text{-CH}_2\text{)-}_n\text{-C}_6\text{H}_5 \) (Polythene) This mechanism is crucial for producing common plastics like polythene.
In simple words: Addition polymerization links small units together without losing any atoms. In the free radical way, a starter chemical makes a chain grow very fast, and then the chain stops when two growing parts meet or become stable.

🎯 Exam Tip: For mechanisms, clearly label each step (initiation, propagation, termination) and show the role of free radicals using appropriate chemical formulas.

 

Question 3. How natural rubber is obtained? Write its composition and structure.
Answer:Natural rubber is first obtained from the latex, which is a milky fluid collected from rubber plants. This latex is a mixture containing about 25% to 40% rubber hydrocarbons, along with proteins and fatty acids that help stabilize it in water. To extract the rubber, these components are made to clump together (coagulate) and then separated by filtering. The solid rubber obtained this way is known as crepe rubber. **Structure and composition:** Natural rubber is a linear polymer made from repeating units of isoprene, specifically 2-methyl-1,3-butadiene. It is chemically known as cis-1,4-polyisoprene, referring to its specific arrangement around the double bonds which gives it its characteristic elasticity. The precise arrangement of these units is what gives natural rubber its unique properties.
In simple words: Natural rubber comes from milky sap of rubber trees. We get it by making the rubber parts stick together and then filtering them. It's made of many small units called isoprene, linked in a special way.

🎯 Exam Tip: When describing natural rubber, remember to mention its source (latex), the coagulation process, its monomer (isoprene), and its chemical name (cis-1,4-polyisoprene).

 

Question 4. Why the molecular mass of polymers is taken as average molecular mass? Explain how many types of average molecular mass can be represented? Explain each type.
Answer:The molecular mass of polymers is usually expressed as an **average molecular mass** because most synthetic polymer samples contain chains of different lengths. This means not all polymer molecules in a sample are identical in size. In contrast, some natural polymers like proteins often have chains of precisely the same length, giving them a definite, not an average, molecular mass. The molecular mass of polymers can be described in two primary ways: (i) **Number Average Molecular Mass (\(M_n\)):** This type of average focuses on the number of molecules present. If \( N_1, N_2, N_3 \) represent the count of molecules with specific molecular masses \( M_1, M_2, M_3 \) respectively, then \( M_n \) is calculated by summing the product of each molecule's count and its mass, then dividing by the total number of molecules.
\( M_n = \frac{N_1M_1+N_2M_2+ N_3M_3+\dots}{N_1 + N_2 + N_3 + \dots} \)
This can also be written as: \( M_n = \frac{\sum N_i M_i}{\sum N_i} \), where \( N_i \) is the number of molecules having molecular mass \( M_i \). (ii) **Weight Average Molecular Mass (\(M_w\)):** This average gives more importance to the heavier molecules in the sample. It is calculated based on the mass contributions of each type of molecule. If \( m_1, m_2, m_3 \) are the total masses of molecules having individual masses \( M_1, M_2, M_3 \) respectively, then \( M_w \) is the sum of the product of each mass contribution and its molecular mass, divided by the total mass.
\( M_w = \frac{m_1M_1 + m_2M_2 + m_3M_3+\dots}{m_1 + m_2 + m_3+\dots} \)
Since \( m_i = N_iM_i \), the formula can be expressed as: \( M_w = \frac{\sum N_i M_i^2}{\sum N_i M_i} \), where \( N_i \) is the number of molecules of mass \( M_i \). Understanding these averages is important for characterizing the properties and uses of different polymer materials.
In simple words: Polymers are usually a mix of different sizes, so we use average molecular masses. Number average counts how many of each size there are, while weight average gives more weight to the bigger molecules.

🎯 Exam Tip: Clearly distinguish between \(M_n\) and \(M_w\) by defining their calculation methods and remembering that \(M_w\) emphasizes the contribution of larger molecules.

 

Question 6. Write method of polymerisations and uses of the following polymers:
1. Bakelite
2. PVC
3. Polyester
4. Nylon - 66
Answer:This question asks for the method of polymerization and uses for four specific polymers. 1. **Bakelite:** This is a **condensation polymer** formed by reacting phenol and formaldehyde. The reaction needs either an acid or a base as a catalyst, which helps speed up the process. * **Uses:** Bakelite with less polymerization is soft and used for glues in plywood and varnishes. Highly polymerized, hard Bakelite is used for making everyday items like combs, fountain pens, electrical switches, and parts for many gadgets. 2. **PVC (Polyvinyl Chloride):** This is an **addition polymer**. It forms when many vinyl chloride monomers join directly, without losing any small molecules, effectively just adding on to each other. * **Uses:** PVC plastic is highly versatile and is used to make bottles, pipes, window frames, and various products for many different industries due to its durability and low cost. 3. **Polyester:** This is a **condensation polymer** made from monomers linked by ester bonds. Common examples are polyethylene terephthalate (PET), formed from terephthalic acid and ethylene glycol. * **Uses:** Polyester is widely used in textiles for clothing because it is durable and wrinkle-resistant. It's also used to make bottles, films, and reinforced plastics due to its strength and resistance to stretching. 4. **Nylon-6,6:** This is also a **condensation polymer** formed from hexamethylenediamine and adipic acid. Small water molecules are released during its formation. * **Uses:** Nylon-6,6 is valued for its strength and abrasion resistance. It's used to make bristles for brushes, strong cords, climbing ropes, and various parts in the automotive industry. It's also blended with cotton or wool to make fabrics more resistant and serves as a glass reinforcing material in safety helmets. This broad range of uses shows its importance.
In simple words: For each polymer, we describe if it's made by simply adding parts or by adding parts and taking out water, and then list its main uses, like Bakelite for switches or Nylon for ropes.

🎯 Exam Tip: For polymer questions, always specify the type of polymerization (addition or condensation) and then list at least two distinct uses to show your understanding of its properties.

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