2.4.4Additional lessons
Polymers — IB Chemistry SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 36 of 98
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 6Monomers and Polymers
Polymers are the basis of plastics, fibres and many natural materials.
Monomer
- Monomer A small molecule that can join to many others to form a long chain.
Polymer
- Polymer A very large molecule made of many repeating units joined by covalent bonds.
Repeat unit
- Repeat unit The smallest section of the chain that repeats along the molecule.
Degree of polymerisation
- Degree of polymerisation This is the number of repeat units in a chain, which can be thousands.
Part 2 of 6Types of Polymerisation
Types of Polymerisation
Addition
- Addition Monomers with a C=C double bond open the double bond and join together without losing any atoms.
Condensation
- Condensation Monomers join and release a small molecule such as water at each link, as in nylon and polyesters.
Natural polymers
- Natural polymers Proteins, starch and DNA are polymers made by living organisms.
Synthetic polymers
- Synthetic polymers Plastics such as poly(ethene) and PVC are made industrially from petrochemicals.
Part 3 of 6Structure and Properties
1
Polymer chains are long and may be tangled together, which makes the material flexible and strong.
2
Chains are attracted to one another by London dispersion forces, which add up over a long chain.
3
Chains with polar groups also have dipole-dipole forces and sometimes hydrogen bonds, which makes them stronger.
4
Long chains with many attractions give higher melting points than small molecules of similar composition.
5
Because there are no free ions or electrons, most polymers are electrical insulators.
| Property | Reason |
|---|---|
| Flexible | chains slide and uncoil |
| Insulator | no free charge carriers |
| Low density | light elements in loosely packed chains |
| Unreactive | strong C–C and C–H bonds |
Part 4 of 6Environmental Issues
Persistence
- Persistence Many synthetic polymers are not biodegradable because microorganisms cannot break the strong C–C bonds.
Waste
- Waste Large quantities of plastic accumulate in landfill and oceans, harming wildlife.
Microplastics
- Microplastics Plastic fragments break into tiny particles that enter food chains.
Responses
- Responses Recycling, reuse, reduced use and development of biodegradable alternatives help reduce the problem.
Part 5 of 6Worked Example
Question Explain why poly(ethene) is unreactive and persists in the environment.
- Poly(ethene) consists of long chains containing only C–C and C–H bonds.
- These bonds are strong and non-polar, so they are not easily attacked by reagents or by the enzymes of microorganisms.
- Consequently the plastic does not biodegrade quickly and remains for a very long time.
Answer Its strong, non-polar C–C and C–H bonds resist chemical and biological attack.
Part 6 of 6Exam Checklist & Tips
2.4.4 – Key Points for the Exam
- Monomer A small molecule that joins with others to form a polymer.
- Polymer A large molecule made from many repeating units.
- Repeat unit The smallest group of atoms that repeats in a polymer chain.
- Biodegradable Able to be broken down by living organisms.
Common Mistakes
- Saying monomers and polymers have the same properties.
- Confusing the repeat unit with the monomer, which may differ in bonding.
- Forgetting that stronger intermolecular forces raise the melting point.
- Assuming all plastics are biodegradable.
Last updated:
\n