Engineering Chemistry: Polymers Quiz

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Questions and Answers

What is the primary monomer that forms natural rubber?

Ethylene

Butadiene

2-methyl-1,3-butadiene (correct)

Polyisoprene

What is a key drawback of raw rubber related to temperature?

It can withstand extreme cold without issues.

It is brittle at room temperature.

It becomes too hard at high temperatures.

It becomes so soft at high temperatures. (correct)

What process significantly enhances the elasticity of rubber?

Polymerization

Coagulation

Vulcanization (correct)

Hydrogenation

Who developed the vulcanization process for rubber?

Charles Goodyear Signup and view all the answers

Which property makes raw rubber unsuitable for use with certain chemicals?

High water absorption capacity Signup and view all the answers

What is the purpose of compounding rubber?

To impart specific properties for particular applications. Signup and view all the answers

Which rubber composition may contain the highest percentage of sulphur?

Battery case rubber Signup and view all the answers

How much sulphur is typically found in tyre rubber?

3 to 5% Signup and view all the answers

Which of the following is NOT a reason for compounding rubber?

To reduce production costs. Signup and view all the answers

What type of rubber may need compounding for improved electrical insulation?

Silicone rubber Signup and view all the answers

What is a common additive used in the compounding process of rubber?

Calcium carbonate Signup and view all the answers

What characteristic can be modified through the compounding of rubber?

Flexibility and durability Signup and view all the answers

Which of these compounds is likely to increase the resilience of rubber?

Carbon black Signup and view all the answers

In rubber compounding, which of the following is primarily used for enhancing strength?

Reinforcement agents Signup and view all the answers

What is one key benefit of compounding rubber with specific additives?

It can create specialized properties for different applications. Signup and view all the answers

What is one classification of polymers based on their origin?

Natural and synthetic Signup and view all the answers

Which polymerization mechanism involves the formation of free radicals?

Free radical polymerization Signup and view all the answers

What does the term 'tacticity' refer to in polymers?

The arrangement of side groups on the polymer backbone Signup and view all the answers

Which of the following is NOT a type of co-polymerization?

Dimer Signup and view all the answers

What is the glass transition temperature (Tg) affected by?

The molecular structure of the polymer Signup and view all the answers

What is the primary distinction between low-density polyethylene (LDPE) and high-density polyethylene (HDPE)?

Molecular branching Signup and view all the answers

Which polymer is produced through condensation polymerization?

Nylon 6:6 Signup and view all the answers

What is the primary purpose of vulcanization in natural rubber processing?

To enhance elasticity and strength Signup and view all the answers

What is the formula for calculating the dispersity index (PDI)?

PDI = Mw / Mn Signup and view all the answers

Which method is NOT used to determine the weight-average molecular mass (Mw)?

Osmotic pressure measurement Signup and view all the answers

What is the number average molecular weight (Mn) for a polymer sample with 50 molecules of 10000, 35 of 12000, and 15 of 14000?

11300 Signup and view all the answers

Which of the following properties is used to determine the number-average molecular mass (Mn)?

Depression in freezing point Signup and view all the answers

How is the degree of polymerization (DP) calculated if the molecular weight of the monomer is 1000 and Mn is 13000?

DP = Mn / Molecular weight of monomer Signup and view all the answers

Which of the following best describes a property of TEFLON?

Exceptionally high chemical resistance Signup and view all the answers

What applications are common for TEFLON?

Non-lubricating bearings Signup and view all the answers

Which molecular weight formula is correct for the calculation of Mw?

Mw = (50x10000) + (35x12000) + (15x14000) Signup and view all the answers

What is the main catalyst used in the manufacturing of HDPE via coordination polymerization?

Ziegler-Natta catalyst Signup and view all the answers

Which statement accurately describes the properties of HDPE compared to LDPE?

HDPE has a higher specific strength due to stronger intermolecular forces. Signup and view all the answers

What is the primary type of polymerization involved in the formation of phenol-formaldehyde (PF) resins?

Condensation polymerization Signup and view all the answers

Which factor significantly influences the nature of the PF resin produced?

Molar ratio of phenol to formaldehyde Signup and view all the answers

What characteristic of novolacs is defined by the phenol to formaldehyde molar ratio?

Linear structure forms when the ratio is > 1, catalyzed by an acid. Signup and view all the answers

Which of the following applications is NOT commonly associated with HDPE?

Thermoplastic elastomers Signup and view all the answers

Which feature of PF resins leads to their thermosetting nature?

Extensive branching during molding operations Signup and view all the answers

What temperature can HDPE withstand continuously without deterioration?

110 °C Signup and view all the answers

Study Notes

Engineering Chemistry Course Details

Course Name: Engineering Chemistry
Course Code: CHY1001
Lecture Series No: 1
Credits: 4
Mode of Delivery: Hybrid

Polymers

Definition: Long chain molecules composed of repeating structural units called monomers.
Classification:
- Origin: Natural (e.g., rubber, cellulose) and Synthetic (e.g., polyethylene, nylon)
- Thermal Behaviour: Thermoplastics (soften on heating and solidify on cooling) and Thermosets (become rigid on heating and cannot be remelted)
Polymerization Reactions:
- Addition Polymerization: Monomers add to form a polymer without the loss of any atoms.
- Condensation Polymerization: Monomers combine with the loss of a small molecule, such as water.
- Co-polymerization: Two or more different monomers combine to form a polymer. Types:
  - Alternating
  - Random
  - Block
  - Graft
Tacticity: Arrangement of substituent groups on polymer chains (Isotactic, Syndiotactic, Atactic)
Functionality: Number of reactive sites on a monomer.
Degree of Polymerization (DP): Average number of monomer units in a polymer chain.
Molecular Weight:
- Number Average Molecular Weight (Mn): Calculated based on the number of molecules of each molecular weight.
- Weight Average Molecular Weight (Mw): Calculated based on the weight of molecules of each molecular weight
- Dispersity Index (PDI): Mw / Mn
- Determination of Mn: Colligative properties (lowering of vapor pressure, osmotic pressure, depression of freezing point, elevation of boiling point)
- Determination of Mw: Light scattering, ultra-centrifugal techniques
Glass Transition Temperature (Tg): The temperature at which a polymer transitions from a rigid, glassy state to a rubbery, flexible state. Factors affecting Tg:
- Chain flexibility
- Intermolecular forces
- Molecular weight
Polythene (LDPE & HDPE)
- Properties of LDPE: Lower density, flexible, easily processed, used in films, bags, packaging.
- Properties of HDPE: Higher density, stronger, more rigid, resistant to chemicals, used in bottles, pipes, containers.
Nylon (6:6, 6, 6:10, 11):
- Properties: Strong, resistant to abrasion, good thermal stability, used in fibers, ropes, gears.
PF Resins:
- Formation: Condensation polymerization, thermosetting polymers.
- Types: Novolacs and Resoles
- Properties: Linear, low molecular weight, soluble, fusible, prepolymers.
- Moulding Process: Branching and cross-linking forming highly cross-linked, insoluble, hard, rigid, infusible products.
Natural Rubber:
- Monomer: Isoprene (2-methyl-1,3-butadiene)
- Properties: High tensile strength, good elasticity, impermeable to gases.
- Drawbacks: Soft at high temperatures, brittle at low temperatures, susceptible to oxidation and degradation.
- Vulcanization: Heating rubber with sulfur (or other vulcanizing agents) to increase elasticity and reduce plasticity.

Teflon (Polytetrafluoroethylene - PTFE)

Properties: Extremely tough, high softening point, high chemical resistance, high density, waxy touch. It can be punched, machined, and drilled.
Uses:
- Insulating materials (motors, transformers, cables, wires, fittings)
- Gaskets, packing, pump parts, tanks, chemical-carrying pipelines, tubing
- Coatings
- Non-lubricating bearings and non-sticking stop-cocks

Compounding of Rubber

Definition: Mixing of raw rubber with other substances to impart specific properties.
Purpose: Improve specific properties of rubber, such as strength, flexibility, and resistance to degradation.

HDPE (High Density Polyethylene)

Properties: High strength-to-density ratio, high density, little branching, strong intermolecular forces, high tensile strength, hard, opaque, heat resistant.
Applications:
- 3D printer filament
- Banners
- Bottle caps
- Chemical resistant piping systems
- Food storage containers
- Fuel tanks for vehicles
- Electrical and plumbing boxes
- Folding chairs and tables

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Description

Test your understanding of polymers in Engineering Chemistry. This quiz covers definitions, classifications, polymerization reactions, and characteristics of various types of polymers. Perfect for students of the CHY1001 course!