i. Which of the following best defines polymers?
Answer: b) Large molecules built up from many smaller molecules called monomers
Explanation: A polymer is a large molecule (macro molecule) composed of many repeating structural units called monomers. The process of joining monomers is called polymerization.
ii. What type of linkage is found in polyamide?
Answer: b) Amide linkage
Explanation: Polyamides (like nylon) contain repeating amide linkages (-CO-NH-) formed by the condensation reaction between a carboxylic acid group and an amine group.
iii. Polyethylene is an example of:
Answer: b) An addition polymer
Explanation: Polyethylene is formed by the addition polymerization of ethene monomers. No small molecule is eliminated during the process.
iv. The repeating unit of the addition polymer formed from ethene is:
Answer: a) -CH₂-CH₂-
Explanation: In addition polymerization, the double bond of ethene opens up, and the monomers link together to form a saturated backbone of -CH₂-CH₂- units.
v. Nylon-6,6 is an example of a:
Answer: b) Polyamide
Explanation: Nylon-6,6 is a synthetic polyamide formed by the condensation polymerization of hexamethylenediamine and adipic acid.
vi. Which of the following processes produces water as a by-product?
Answer: b) Condensation polymerization
Explanation: In condensation polymerization, monomers with at least two functional groups react, and a small molecule like water (or HCl, methanol) is eliminated as a by-product.
vii. Which statement is not true about PET?
Answer: b) It is a polyamide (Note: PET is a polyester. It can be recycled. It is used in textiles and bottles. Option b is the incorrect
statement.)
viii. Which of the following is a major environmental challenge caused by plastics?
Answer: c) They accumulate in oceans
Explanation: Non-biodegradable plastics persist in the environment for hundreds of years, accumulating in oceans and harming marine life.
ix. Polyesters are formed from:
Answer: b) Dicarboxylic acids and diols
Explanation: Polyesters are formed by the condensation polymerization of a dicarboxylic acid and a diol (dialcohol), producing ester linkages.
x. Which of the following is NOT a property of plastics?
Answer: c) They are easily decomposed by microorganisms
Explanation: Most plastics are non-biodegradable and resist decomposition by microorganisms, which is why they persist in the environment.
i. Define a polymer.
Answer: A polymer is a large molecule (macro molecule) of high molecular mass formed by the chemical combination of many smaller repeating units called monomers. The process of forming a polymer is called polymerization. Polymers can be natural (like cellulose, proteins, and rubber) or synthetic (like polythene, nylon, and PVC). The properties of a polymer depend on its molecular structure, chain length, and the type of bonding between the chains. They are essential materials in modern daily life.
ii. What is a monomer?
Answer: A monomer is a small, simple molecule that can chemically bond with other identical or similar molecules to form a large molecule called a polymer. The word "monomer" comes from the Greek words "mono" (one) and "meros" (part). For example,
ethene (CH₂=CH₂) is the monomer of polythene, and glucose is the monomer of starch and cellulose. Monomers must have at least two reactive sites (like a double bond or two functional groups) to undergo polymerization.
iii. What is the repeating unit in polyethylene.
Answer: The repeating unit in polyethylene is the -CH₂-CH₂- unit. In the polymerization of ethene (CH₂=CH₂), the carbon-carbon double bond breaks open, and thousands of ethene molecules join together to form a long, saturated hydrocarbon chain. The general formula for polyethylene can be written as [-CH₂-CH₂-]ₙ, where 'n' represents the number of repeating monomer units in the polymer chain. This simple repeating unit gives polyethylene its characteristic properties.
iv. Explain what is meant by addition polymerization.
Answer: Addition polymerization is a type of polymerization in which unsaturated monomer molecules containing carbon-carbon double bonds (alkenes) add to one another without the elimination of any small molecule (like water or HCl) as a by-product. The monomers simply add together to form a long chain, and the polymer has the same empirical formula as the monomer. The reaction is usually initiated by a free radical, cation, or anion, and proceeds through a chain reaction mechanism involving initiation, propagation, and termination.
v. Describe the process of condensation polymerization.
Answer: Condensation polymerization is a type of polymerization in which monomers containing at least two functional groups (such as -COOH, -OH, -NH₂) react with each other to form a polymer, with the simultaneous elimination of a small molecule such as water, alcohol, or hydrogen chloride. This is a step-growth process where the polymer chain grows gradually as monomers combine. Examples include the formation of nylon (a polyamide) from a diamine and a diacid, and the formation of PET (a polyester) from a diol and a diacid.
vi. Name the linkage found in polyesters.
Answer: The linkage found in polyesters is the ester linkage (-COO-). It is formed by the condensation reaction between a carboxylic acid group (-COOH) of one monomer and a hydroxyl group (-OH) of another monomer. For example, in the formation of PET,
terephthalic acid reacts with ethylene glycol to form an ester linkage, releasing water as a by-product. The ester linkage gives polyesters their characteristic properties like strength, durability, and resistance to chemicals.
vii. What are the monomers required to form nylon?
Answer: The monomers required to form nylon-6,6 are:
1. Hexamethylenediamine: A diamine with the formula H₂N-(CH₂)₆-NH₂.
2. Adipic acid: A dicarboxylic acid with the formula HOOC-(CH₂)₄-COOH. These two monomers undergo condensation polymerization to form nylon-6,6, a polyamide. The reaction produces water as a by-product. The resulting polymer has strong hydrogen bonding between its chains, giving it high tensile strength and durability.
viii. Explain one environmental challenge associated with the disposal of plastics in landfills.
Answer: One major environmental challenge associated with the disposal of plastics in landfills is that plastics are non- biodegradable. They do not decompose by the action of microorganisms, so they persist in the environment for hundreds to thousands of years. This leads to the accumulation of massive amounts of plastic waste in landfills, taking up valuable space and causing land pollution. Additionally, as plastics slowly break down into microplastics, they can contaminate soil and groundwater.
ix. Describe the structure of PET.
Answer: PET (Polyethylene Terephthalate) is a linear polyester. Its structure consists of repeating units joined by ester linkages. The repeating unit is formed by the condensation of terephthalic acid (a benzene ring with two -COOH groups) and ethylene glycol (a two-carbon diol). The structure can be represented as: [-CO-C₆H₄-CO-O-CH₂-CH₂-O-]ₙ. The benzene rings in the chain provide rigidity, while the flexible ethylene glycol segments provide flexibility. This unique structure gives PET its desirable properties like strength,
lightness, and thermal stability.
x. Why is PET considered recyclable?
Answer: PET is considered recyclable because it is a thermoplastic polymer. This means it can be softened and remelted upon heating and re-hardened upon cooling, without undergoing any significant chemical change. This property allows used PET bottles and containers to be collected, cleaned, melted, and remolded into new products (like fibers, sheets, and new bottles). This process is called mechanical recycling. PET can also be chemically recycled by breaking it down into its original monomers (terephthalic acid and ethylene glycol).
xi. How are addition polymers formed from monomers?
Answer: Addition polymers are formed from monomers containing carbon-carbon double bonds (alkenes). The process involves a chain reaction mechanism:
1. Initiation: An initiator (like a free radical) attacks the double bond of a monomer, creating a reactive species.
2. Propagation: The reactive species attacks another monomer, forming a new bond and regenerating the reactive site. This process repeats thousands of times, rapidly growing the polymer chain.
3. Termination: Two growing chains react with each other, or a chain reacts with an initiator, stopping the growth. The result is a long, saturated hydrocarbon chain with the same empirical formula as the monomer.
xii. What is released during the formation of condensation polymers?
Answer: During the formation of condensation polymers, a small molecule such as water (H₂O), hydrogen chloride (HCl), or methanol (CH₃OH) is released as a by-product. For example, in the formation of nylon, water is released when the amine group reacts with the carboxylic acid group. In the formation of some other polymers, HCl might be released. This elimination of a small
molecule is the defining characteristic of condensation polymerization.
xiii. What is the repeating unit in the polymer formed from ethylene glycol and terephthalic acid?
Answer: The polymer formed from ethylene glycol and terephthalic acid is PET (Polyethylene Terephthalate). The repeating unit is: [-CO-C₆H₄-CO-O-CH₂-CH₂-O-]ₙ This unit consists of a terephthalic acid moiety (benzene ring with two carbonyl groups) and an ethylene glycol moiety (two-carbon chain with two oxygen atoms). The two monomers are linked by ester bonds.
xiv. Why is PET widely used in textiles?
Answer: PET is widely used in textiles (often called polyester fabric) due to its excellent properties:
1. Strength and Durability: It has high tensile strength and is resistant to stretching and shrinking.
2. Wrinkle Resistance: It is wrinkle-resistant and easy to care for.
3. Quick Drying: It is hydrophobic, so it dries quickly.
4. Color Fastness: It holds dyes well and resists fading.
5. Versatility: It can be blended with natural fibers like cotton to improve their properties. These properties make PET ideal for clothing, bedding, and other textile applications.
xv. What is a key difference between polyamides and polyesters?
Answer: The key difference between polyamides and polyesters is the type of linkage that connects the monomers:
Polyamides: Contain amide linkages (-CO-NH-). They are formed by the condensation of a dicarboxylic acid and a diamine.
Polyesters: Contain ester linkages (-COO-). They are formed by the condensation of a dicarboxylic acid and a diol. This difference in linkage affects their chemical properties, such as their reactivity and susceptibility to hydrolysis.
xvi. Why is nylons strength important for its application?
Answer: The high strength of nylon is crucial for its applications because it allows the material to withstand significant mechanical stress, tension, and wear. This strength arises from the strong hydrogen bonding between the polyamide chains. Because of this, nylon is used in applications where durability is essential, such as in carpets, ropes, seat belts, parachutes, and as a replacement for metal in gears and bearings. Its strength also makes it suitable for clothing that must withstand frequent use and washing.
xvii. What is released during the formation of condensation polymers? (This is a repeat of Question xii. The answer is the same.)
xviii. Give an example of a condensation polymer.
Answer: An example of a condensation polymer is Nylon-6,6. It is formed by the condensation polymerization of hexamethylenediamine (a diamine) and adipic acid (a dicarboxylic acid). During the reaction, water is eliminated as a by-product. Another example is PET (Polyethylene Terephthalate), formed from ethylene glycol and terephthalic acid, also releasing water.
xix. How do the properties of plastics depend on their polymer structure?
Answer: The properties of plastics depend heavily on their polymer structure:
Chain Length: Longer chains generally increase strength, toughness, and melting point. Branching: Branched chains reduce intermolecular forces, making the plastic softer and more flexible (e.g., LDPE). Linear
chains pack closely, making the plastic harder and denser (e.g., HDPE). Cross-linking: Strong covalent bonds between chains create rigid, infusible thermosetting plastics (e.g., Bakelite). Intermolecular Forces: Stronger forces between chains (like hydrogen bonding in nylon) increase strength and melting point. These structural features determine the physical, mechanical, and thermal properties of the plastic.
xx. What are two environmental challenges associated with plastic disposal?
Answer: Two major environmental challenges associated with plastic disposal are:
1. Accumulation in Landfills and Oceans: Plastics are non-biodegradable and persist in the environment for hundreds of years, taking up space in landfills and accumulating in oceans, harming marine life. Microplastics: Plastics break down into tiny particles called microplastics, which enter the food chain and can have toxic effects on organisms.
2. Toxic Emissions: Burning plastic waste releases toxic gases and greenhouse gases (like CO₂ and dioxins), contributing to air pollution and climate change.
i. Describe in detail the process of addition polymerization, giving an example of an addition polymer and its repeating unit.
Answer: Addition polymerization is a process in which unsaturated monomers (containing carbon-carbon double bonds) join together to form a large polymer molecule without the elimination of any small molecule. The polymer has the same empirical formula as the monomer. The process is a chain reaction that occurs in three stages: initiation, propagation, and termination.
1. Initiation:
The reaction is initiated by a free radical initiator (e.g., benzoyl peroxide) or by heat/light. The initiator attacks the double bond of a monomer, breaking the π bond and creating a new radical.
For example, with ethene (CH₂=CH₂) and a radical (R•): R• + CH₂=CH₂ [source symbol unavailable] R-CH₂-CH₂•
2. Propagation:
The new radical attacks another monomer, forming a new bond and regenerating the radical. This process repeats thousands of times, rapidly growing the polymer chain.
R-CH₂-CH₂• + CH₂=CH₂ [source symbol unavailable] R-CH₂-CH₂-CH₂-CH₂• (and so on)
3. Termination:
The chain growth stops when two growing chains react with each other, or when a chain reacts with an initiator molecule. For example: R-(CH₂)ₙ• + •(CH₂)ₘ-R [source symbol unavailable] R-(CH₂)ₙ₊ₘ-R
Example of an Addition Polymer: Polyethene (Polyethylene)
Monomer: Ethene (CH₂=CH₂) Polymer: Polyethene [-CH₂-CH₂-]ₙ Repeating Unit: -CH₂-CH₂-
In summary, addition polymerization is a chain reaction that joins unsaturated monomers to form a saturated polymer backbone without releasing any by-products.
ii. Explain how condensation polymerization works, using the formation of polyester as an example. Include the reactants and the type of linkage formed.
Answer: Condensation polymerization is a type of polymerization in which monomers containing at least two functional groups react with each other to form a polymer, with the simultaneous elimination of a small molecule (e.g., water, alcohol, or HCl) as a by-product. This is a step-growth process.
1. General Mechanism:
The monomers must have at least two reactive functional groups (e.g., -COOH, -OH, -NH₂). The reaction occurs between the functional groups of different monomers, forming a new covalent bond and releasing a small molecule. The polymer chain grows gradually as monomers combine.
2. Example: Formation of a Polyester (PET):
Reactants:
Terephthalic acid: A dicarboxylic acid. Ethylene glycol: A diol (dialcohol).
Reaction: The carboxylic acid group of terephthalic acid reacts with the hydroxyl group of ethylene glycol. A ester linkage (-COO-) is formed, and a molecule of water (H₂O) is eliminated. Equation: n HOOC-C₆H₄-COOH + n HO-CH₂-CH₂-OH [source symbol unavailable] [-CO-C₆H₄-CO-O-CH₂-CH₂-O-]ₙ + 2n H₂O
3. Linkage:
The linkage formed is the ester linkage (-COO-).
In summary, condensation polymerization is a step-growth process that joins monomers with two functional groups, releasing a small molecule and forming a polymer with specific linkages like ester or amide.
iii. Discuss the differences between addition and condensation polymerization, giving examples of polymers formed by each process.
Answer: Addition polymerization and condensation polymerization are the two main types of polymerization. They differ significantly in their mechanisms, monomers, and by-products.
| Feature | Addition Polymerization | Condensation Polymerization |
| Monomer Type | Monomers must contain C=C double bonds (alkenes). | Monomers must have at least two functional groups (e.g., - COOH, -OH, -NH₂). |
| By-product | No small molecule is eliminated. | A small molecule (like H₂O, HCl, or CH₃OH) is eliminated. |
| Mechanism | Chain-growth (free radical, ionic). | Step-growth. |
| Polymer Structure | Backbone is a continuous chain of carbon atoms. | Backbone contains heteroatoms (like O, N) at regular intervals. |
| Empirical Formula | Polymer has the same empirical formula as the monomer. | Polymer has a different empirical formula than the monomers. |
| Examples | Polyethene, PVC, Teflon. | Nylon-6,6, PET, Bakelite. |
In summary, addition polymerization involves the direct joining of unsaturated monomers, while condensation polymerization involves the reaction of functional groups with the elimination of a small molecule.
iv. Evaluate the environmental impacts of plastic disposal, covering landfills, ocean accumulation, and the formation of toxic gases from burning.
Answer: Plastic disposal poses significant environmental challenges due to the non-biodegradable nature of most plastics.
1. Landfills:
Plastics take up huge volumes in landfills, as they do not decompose. This reduces available space for other waste and can lead to soil contamination. As plastics slowly degrade, they can release harmful chemicals and microplastics into the soil and groundwater.
2. Ocean Accumulation:
Millions of tons of plastic waste enter the oceans each year. This poses a severe threat to marine life through entanglement and ingestion. Plastic waste breaks down into microplastics, which are consumed by plankton and enter the food chain, eventually reaching humans. Large garbage patches, like the Great Pacific Garbage Patch, disrupt marine ecosystems.
3. Toxic Gases from Burning:
Burning plastics releases toxic gases such as carbon monoxide, dioxins, and furans. These are harmful to human health and contribute to air pollution. Burning plastics also releases greenhouse gases like CO₂, contributing to climate change.
In summary, plastic disposal has severe environmental consequences. Sustainable alternatives and improved recycling are essential to mitigate these impacts.
v. Outline the importance of polymers in the textile industry, giving examples of specific polymers used and their properties that make
them suitable for textile applications.
Answer: Polymers are essential in the textile industry, providing fibers with a wide range of properties suitable for various applications.
1. Polyesters (PET):
Properties: Strong, durable, wrinkle-resistant, quick-drying, and colorfast. Applications: Used in clothing, bedding, and as a blend with cotton.
2. Polyamides (Nylon):
Properties: High tensile strength, elasticity, abrasion resistance, and quick-drying. Applications: Used in activewear, hosiery, carpets, and ropes.
3. Polyacrylonitrile (Acrylic):
Properties: Soft, warm, lightweight, and resistant to sunlight and chemicals. Often used as a wool substitute. Applications: Used in sweaters, blankets, and outdoor fabrics.
4. Polypropylene:
Properties: Lightweight, moisture-resistant, and durable. Applications: Used in thermal underwear, sportswear, and ropes.
5. Elastane (Spandex/Lycra):
Properties: Highly elastic and stretchable, capable of stretching up to 500% without breaking. Applications: Used in sportswear, swimwear, and fitted clothing.
In summary, synthetic polymers have revolutionized the textile industry by providing fibers with superior performance properties.
vi. What process allows PET to be reused? Why is this process beneficial?
Answer: The process that allows PET to be reused is recycling, which can be done through mechanical or chemical means.
1. Mechanical Recycling:
PET is collected, sorted, cleaned, and shredded into flakes. The flakes are then melted and remolded into new products (like fibers, sheets, and new bottles). This process is possible because PET is a thermoplastic (it softens on heating and hardens on cooling without significant chemical change).
2. Chemical Recycling:
PET is broken down into its original monomers (terephthalic acid and ethylene glycol) through chemical reactions (like glycolysis or hydrolysis). The monomers are then re-polymerized to produce virgin-quality PET.
Benefits:
Conserves Resources: Reduces the need for new raw materials (petroleum). Reduces Waste: Keeps plastic out of landfills and oceans. Energy Savings: Requires less energy than producing new PET. Environmental Protection: Reduces pollution and greenhouse gas emissions.
In summary, recycling PET is highly beneficial for sustainability and environmental protection.
vii. Assess the role of polymers such as nylon and PET in the textile industry. How do their specific properties make them suitable for different applications?
Answer: Nylon and PET (polyester) are two of the most important synthetic polymers in the textile industry. Their distinct properties make them suitable for a wide range of applications.
1. Nylon (Polyamide):
Properties: Exceptional tensile strength, high elasticity, excellent abrasion resistance, and good resistance to chemicals and heat. Applications: Used in hosiery, activewear, swimwear, carpets, ropes, and parachutes. Its strength makes it ideal for high- stress applications.
2. PET (Polyester):
Properties: High strength, wrinkle resistance, quick-drying, and excellent colorfastness. It is also resistant to stretching and shrinking. Applications: Used in clothing (often blended with cotton), bedding, curtains, and upholstery. Its wrinkle resistance makes it ideal for easy-care garments.
In summary, the diverse properties of nylon and PET make them indispensable in the textile industry, offering performance and durability that natural fibers alone cannot provide.
viii. Evaluate the differences between addition and condensation polymerization in terms of the types of monomers used, the nature of the polymer chains formed, and the by-products produced. (This is a repeat of Question iii. Please refer to the detailed comparison table above.)
ix. Analyse the environmental impact of addition and condensation polymers. Compare their biodegradability and discuss how this affects their disposal and accumulation in the environment.
Answer:
Both addition and condensation polymers have significant environmental impacts, primarily due to their persistence in the environment.
1. Addition Polymers (e.g., Polyethene, PVC):
Biodegradability: Generally non-biodegradable due to their strong C-C backbone, which microorganisms cannot easily break down. Disposal and Accumulation: They accumulate in landfills and oceans for hundreds of years, causing land and water pollution. They break down into harmful microplastics.
2. Condensation Polymers (e.g., Nylon, PET):
Biodegradability: Some condensation polymers (like polyesters and polyamides) are more susceptible to hydrolysis than addition polymers. However, in natural environments, they are still very slow to degrade. Disposal and Accumulation: They also accumulate in landfills. However, many can be chemically recycled (e.g., PET) by breaking them back into monomers.
In summary, while condensation polymers are slightly more biodegradable than addition polymers, both contribute significantly to environmental pollution. Improved recycling and the development of biodegradable polymers are essential.
1. Considering the environmental challenges posed by plastics, propose a sustainable strategy for managing plastic waste, including recycling and alternative materials.
Answer:
Reduce: Encourage the use of reusable bags, bottles, and containers to reduce single-use plastic consumption.
Recycle: Implement efficient mechanical and chemical recycling programs. Chemical recycling can convert plastics back to monomers or fuels. Biodegradable Alternatives: Promote the use of bioplastics (e.g., PLA, PHA) made from renewable resources that can biodegrade. Legislation: Ban single-use plastics and enforce Extended Producer Responsibility (EPR) policies. Education: Raise public awareness about the environmental impact of plastics.
2. Analyse the impact of microplastics in marine environments and discuss potential solutions to mitigate their effects.
Answer:
Impact: Microplastics are ingested by marine organisms, causing physical damage, starvation, and exposure to toxic chemicals. They bioaccumulate up the food chain, reaching humans. Solutions:
Improve wastewater treatment to capture microplastics. Ban microbeads in cosmetics. Develop biodegradable plastics. Support large-scale ocean cleanup initiatives.
3. Evaluate the need for developing biodegradable polymers to replace traditional plastics.
Answer:
Need: Traditional plastics persist for centuries, polluting land and oceans. Biodegradable polymers (like PLA, PHA) can be broken down by microorganisms into natural substances (CO₂, water, biomass). Benefits: Reduce landfill waste, lower carbon footprint, and reduce harm to wildlife.
Challenges: Higher cost, limited availability, and need for specific conditions (industrial composting) for degradation.
4. Imagine you are an environmental scientist tasked with reducing oceanic plastic pollution. Analyse the key sources of plastic waste that end up in the oceans.
Answer:
Land-based sources:
Inadequate waste management (littering, illegal dumping). Stormwater runoff carrying plastic debris. Industrial discharge.
Ocean-based sources:
Fishing gear (ghost nets). Shipping and boating activities.
Solutions: Improve waste management infrastructure, enforce regulations, and promote international cooperation.
5. Polyamide polymers like nylon are used extensively in various applications. Analyse the properties that make nylon a preferred material for such uses.
Answer: Nylon is preferred for its:
High Tensile Strength: Due to hydrogen bonding between chains. Elasticity: It can stretch and return to its original shape. Abrasion Resistance: It is durable and withstands wear. Quick Drying: It is hydrophobic.
Resistance to Chemicals: It resists damage from many chemicals. These properties make it ideal for textiles, ropes, and mechanical parts.
6. Consider a monomer (such as ethylene or terephthalic acid and ethylene glycol), and deduce the structure of the corresponding polymers that can be made from the.
Answer:
From Ethylene (CH₂=CH₂): Addition polymerization yields Polyethylene [-CH₂-CH₂-]ₙ. From Terephthalic Acid (HOOC-C₆H₄-COOH) and Ethylene Glycol (HO-CH₂-CH₂-OH): Condensation polymerization yields PET [-CO-C₆H₄-CO-O-CH₂-CH₂-O-]ₙ. From Adipic Acid (HOOC-(CH₂)₄-COOH) and Hexamethylenediamine (H₂N-(CH₂)₆-NH₂): Condensation polymerization yields Nylon-6,6 [-CO-(CH₂)₄-CO-NH-(CH₂)₆-NH-]ₙ.
