This question is about the structural isomers shown - AQA - A-Level Chemistry - Question 3 - 2020 - Paper 2
Question 3
This question is about the structural isomers shown.
1. Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).
State the e... show full transcript
Worked Solution & Example Answer:This question is about the structural isomers shown - AQA - A-Level Chemistry - Question 3 - 2020 - Paper 2
Step 1
Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).
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Answer
The isomers that would react with acidified potassium dichromate(VI) are Q, R, S, and T. The expected observation is that the orange solution turns green, indicating a reduction reaction.
Step 2
Identify the isomer(s) that would react with Tollens' reagent.
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Answer
The isomer that would react with Tollens' reagent is T. The expected observation is the formation of a silver mirror on the surface of the test tube.
Step 3
Identify the isomer(s) that would react with ethanolic acid.
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Answer
The isomer that would react with ethanolic acid is S.
Step 4
Suggest a simple way to detect if the ethanolic acid reacts with each isomer.
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Answer
A simple way to detect this is to observe for any effervescence or gas evolution when the mixture is poured into sodium hydrogencarbonate solution.
Step 5
Give a reason why the mixture is poured into sodium hydrogencarbonate solution.
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The reason for pouring the mixture into sodium hydrogencarbonate solution is to neutralize any excess acid that may be present.
Step 6
State the type of structural isomerism shown by isomers P, Q, R and S.
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Answer
The type of structural isomerism shown by isomers P, Q, R, and S is position isomerism.
Step 7
Describe fully how infrared spectra can be used to distinguish between isomers S, R and T.
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Isomer S has an -OH absorbance peak in the infrared region at 3230-3550 cm⁻¹, while isomer R has a characteristic C=O peak around 1680-1750 cm⁻¹. Isomer T exhibits uniquely in the fingerprint region or below 1500 cm⁻¹. By comparing these spectra and looking for distinctive peaks, one can effectively distinguish between the isomers.
Step 8
State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.
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Mass spectrometry using electrospray ionisation is not suitable because all the isomers have the same molecular ion (M) peak, making it impossible to differentiate them based on mass alone.
