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The outer layers of some golf balls are made from a polymer called polyisoprene - AQA - A-Level Chemistry - Question 3 - 2019 - Paper 2
Question 3
The outer layers of some golf balls are made from a polymer called polyisoprene. The isoprene monomer is a non-cyclic branched hydrocarbon that contains 88.2 % carbo... show full transcript
Worked Solution & Example Answer:The outer layers of some golf balls are made from a polymer called polyisoprene - AQA - A-Level Chemistry - Question 3 - 2019 - Paper 2
Step 1
Deduce the molecular formula and suggest a possible structure.
Answer
To deduce the molecular formula, we start with the empirical formula. Given that the empirical formula of isoprene is the same as its molecular formula, we can conclude:
The empirical formula can be calculated based on the percentage of carbon: 88.2% carbon implies that the remaining percentage is hydrogen:
Assuming 100 g of isoprene:
- Mass of Carbon = 88.2 g
- Mass of Hydrogen = 100 g - 88.2 g = 11.8 g
Next, we calculate the number of moles:
- Moles of Carbon = 88.2 g / 12.01 g/mol = 7.35 mol
- Moles of Hydrogen = 11.8 g / 1.008 g/mol = 11.8 mol
We take the smallest number of moles, which is 7.35, and divide both by 7.35:
- C = 7.35 / 7.35 = 1
- H = 11.8 / 7.35 = 1.6
To get whole numbers, we multiply by 5:
- C = 5
- H = 8
Therefore, the molecular formula is C₅H₈. A possible structure is the branched form:
H H
\ /
C
/ \
H C - H
/ \
H H
This represents 2-methyl-1,3-butadiene.
Step 2
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Step 4
Step 5
Give a reason why this type of stereoisomerism arises.
Answer
Stereoisomerism arises due to restricted rotation around the C=C double bond. This restriction allows for the occurrence of cis and trans configurations, resulting in different spatial arrangements of the substituents attached to the double-bonded carbons.
Step 6
Explain why these golf balls do not biodegrade.
Answer
Golf balls do not biodegrade because they are made from synthetic polymers like polyisoprene that are chemically stable and resistant to microbial degradation. Carbon-carbon bonds in these polymers are non-polar and not easily attacked by water or reactive chemicals in the environment, which makes them durable and long-lasting.