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CHEMISTRY, M7 2025 HSC 28

Kevlar and polystyrene are two common polymers.

A section of their structures is shown.
 

     

  1. Kevlar is produced through a reaction of two different monomers, one of which is shown. Draw the missing monomer in the box provided.   (1 mark)

  1. Kevlar chains are hard to pull apart, whereas polystyrene chains are not.
  2. With reference to intermolecular forces, explain the difference in the physical properties of the two polymers.   (3 marks)

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a.    
           

b.    The physical differences between the two polymers are:

  • Kevlar chains are very hard to pull apart because the polymer contains many amide groups that can form strong hydrogen bonds between neighbouring chains. These strong forces hold the chains tightly together, making Kevlar rigid and very strong.
  • The close packing of the chains also gives Kevlar a high melting point, because a large amount of energy is required to break the hydrogen bonds.
  • Polystyrene, on the other hand, does not contain groups that can form hydrogen bonds. Its polymer chains are mostly non-polar, so the only forces between the chains are weak dispersion forces.
  • These weaker attractions mean the chains can slide past each other, making polystyrene much softer, brittle, and it also has a lower melting point than Kevlar. Because the forces between chains are weak, polystyrene is much easier to pull apart compared to Kevlar.
Show Worked Solution

a.    
           

b.    The physical differences between the two polymers are:

  • Kevlar chains are very hard to pull apart because the polymer contains many amide groups that can form strong hydrogen bonds between neighbouring chains. These strong forces hold the chains tightly together, making Kevlar rigid and very strong.
  • The close packing of the chains also gives Kevlar a high melting point, because a large amount of energy is required to break the hydrogen bonds.
  • Polystyrene, on the other hand, does not contain groups that can form hydrogen bonds. Its polymer chains are mostly non-polar, so the only forces between the chains are weak dispersion forces.
  • These weaker attractions mean the chains can slide past each other, making polystyrene much softer, brittle, and it also has a lower melting point than Kevlar. Because the forces between chains are weak, polystyrene is much easier to pull apart compared to Kevlar.

CHEMISTRY, M7 2025 HSC 16 MC

A single straight strand of polyester was produced through a condensation reaction of 1000 molecules of 3-hydroxypropanoic acid, \(\ce{HOCH2CH2COOH}\).

What is the approximate molar mass of the strand (in g mol\(^{-1}\) )?

  1. 72 062
  2. 72 080
  3. 90 060
  4. 90 078
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\(B\)

Show Worked Solution
  • The molar mass of 3-hydroxypropanoic acid \(= 6(1.008) +3(16.00) + 3(12.01) = 90.078\ \text{g mol}^{-1}\).
  • When 1000 molecules of 3-hydroxypropanoic acid undergoes condensation reactions, 999 molecules of water are formed as by-products.
  • Hence the molar mass of the polymer strand can be calculated by:
\(MM_{\text{strand}}\) \(=MM_{\text{monomers}}-MM_{\text{water}}\)  
  \(=90.078 \times 1000 -18.016 \times 999\)  
  \( = 72\ 080\ \text{g mol}^{-1}\)  

\(\Rightarrow B\)

CHEMISTRY, M7 2024 HSC 14 MC

Glycine, an amino acid, can react with itself or other amino acid monomers to form silk, a natural polymer.

Glycine has the structure:
 

       

A section of silk polymer is shown.
 

Which monomer could react with glycine to form this section of silk polymer?
 
 

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\(B\)

Show Worked Solution
  • The silk polymer shown is a condensation polymer and also a polyamide formed from monomers containing the amine and carboxylic functional groups.
  • During the formation of the polymer, the \(\ce{NH2}\) amine group will lose a hydrogen and that hydrogen will form a water molecule with the hydroxyl group.
  • The part of glycine that remains in the polymer is \(\ce{NHCH2CO}\).
  • The second repeating unit in the polymer is \(\ce{NHCHCH3CO}\).
     

\(\Rightarrow B\)

CHEMISTRY, M7 2016 VCE 12 MC

A condensation reaction involving 200 glucose molecules, \(\ce{C6H12O6}\), results in a polysaccharide. The molar mass, in g mol\(^{-1}\), of the polysaccharide is

  1. 36 000
  2. 35 982
  3. 32 418
  4. 32 400
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\(C\)

Show Worked Solution
  • 200 \(\ce{C6H12O6}\) molecules react to form a polysaccharide
  • 199 \(\ce{H2O}\) molecules are released in this condensation polymerisation
  •    \(\ce{MM(C6H12O6) = 180.0\ \text{g mol}^{-1} }\)
  •    \(\ce{MM(H2O) = 18.0\ \text{g mol}^{-1} }\)
  •    \(\ce{MM(\text{polysaccharide})}= 200 \times 180.0-199 \times 18.0= 32\ 418\ \text{g mol}^{-1}\)

\(\Rightarrow C\)

CHEMISTRY, M7 EQ-Bank 27

Contrast ONE addition polymer and ONE condensation polymer in terms of their structures, properties and uses. Include structural formulae in your answers.   (7 marks)

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Addition polymer – polyethylene. Condensation polymer – nylon.

Structures

  • Polyethylene is made by the addition of ethylene monomers with the following structural formula:

  • Nylon is a condensation polymer made from 1,6-diaminohexane and adipic acid, producing a by-product of water molecules. It has the following structural formula.

Properties

  • Polyethylene is inexpensive, weatherproof and relatively resistant to chemicals.
  • There are two main types of polyethylene which have different properties. Low-density polyethylene (LDPE) is semi-rigid while high density polyethylene (HDPE) is fluid.
  • Nylon is strong and relatively resistant to moisture absorptivity. It is longer lasting than polyethylene, resistant to chemicals and is used to make nylon fibre.

Applications

  • LDPE is used to produce products such as plastic soft drink bottles, flexible water pipes and cling wrap. HDPE’s fluidity make it an appropriate material for producing shopping bags, plastic crates and drums for storage.
  • Nylon is very versatile in its manufacturing uses. It is a common input for clothing, can be used for injection-moulded parts for vehicles and also as reinforcement for rubber tyres. 
  • Nylon is also used as the main material input for nylon thread which has a myriad of uses, including stitching for clothes and the production of rope.
Show Worked Solution

Addition polymer – polyethylene. Condensation polymer – nylon.

Structures

  • Polyethylene is made by the addition of ethylene monomers with the following structural formula:

  • Nylon is a condensation polymer made from 1,6-diaminohexane and adipic acid, producing a by-product of water molecules. It has the following structural formula.

Properties

  • Polyethylene is inexpensive, weatherproof and relatively resistant to chemicals.
  • There are two main types of polyethylene which have different properties. Low-density polyethylene (LDPE) is semi-rigid while high density polyethylene (HDPE) is fluid.
  • Nylon is strong and relatively resistant to moisture absorptivity. It is longer lasting than polyethylene, resistant to chemicals and is used to make nylon fibre.

Applications

  • LDPE is used to produce products such as plastic soft drink bottles, flexible water pipes and cling wrap. HDPE’s fluidity make it an appropriate material for producing shopping bags, plastic crates and drums for storage.
  • Nylon is very versatile in its manufacturing uses. It is a common input for clothing, can be used for injection-moulded parts for vehicles and also as reinforcement for rubber tyres. 
  • Nylon is also used as the main material input for nylon thread which has a myriad of uses, including stitching for clothes and the production of rope.

CHEMISTRY, M7 2020 HSC 12 MC

The structure of part of a polymer chain is shown.
 


 

Which statement best explains why plastics made from this polymer require a temperature of approximately 250°C before they begin to soften?

  1. The carbon–carbon bonds in the polymer chains are strong.
  2. The carbon–hydrogen bonds in the polymer chains are strong.
  3. Extensive dipole–dipole and dispersion forces exist between the polymer chains.
  4. Extensive hydrogen bonds and dispersion forces exist between the polymer chains.
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`C`

Show Worked Solution
  • The polymer diagram shows the following intermolecular forces: dipole-dipole forces and dispersion forces.
  • High temperatures break some of the intermolecular forces, causing the plastic to soften (polyesters can’t form `text{H}`-bonds).

`=> C`

CHEMISTRY, M7 2022 HSC 18 MC

A low molecular weight biopolymer is being investigated for its suitability for medical use. In one trial a molecular weight of `2900 pm 100\ text{g}\ text{mol}^(-1)` proved to be optimum.

A section of this biopolymer is shown.
 

Which will produce the suitable biopolymer?
 

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`D`

Show Worked Solution

This polymer is a condensation polymer, meaning that it is formed through the reaction between monomers that consist of a carboxylic acid and/or an alcohol functional group, with the elimination of water.

Thus, if `text{n}` monomers react to form this polyester, `text{(n – 1)}` molecules of water would be eliminated.

Calculating their molar masses:

`text{n}\ xx\ text{monomers}` `= text{polymer} + text{(n – 1)} xx text{H}_2 text{O}`
`text{n} xx (90.078)` `= 2900 + text{(n – 1)} xx (18.016)`
`text{n}(90.078-18.016)` `=2900-18.016`
`:.\ text{n}` `=2881.984/72.062=39.99…`

 
`=> D`


♦♦ Mean mark 23%.

CHEMISTRY, M7 2021 HSC 10 MC

The structure of part of a polymer chain is shown.
 

 
Which is the monomer of this polymer?
 

 

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`B`

Show Worked Solution
  • The polymer formed is a condensation polymer, where the by-product is water (`text{H}_2 text{O}`).
  • From the polymer shown, the alcohol functional group must ie on the second carbon atom, and the carboxylic functional group must lie on the first carbon atom.
  • Thus, could only be formed from monomer B.

`=> B`