Pearson Edexcel A Level · Chemistry (9CH0)
5 multiple-choice questions marked as you go, and 3 written questions with worked solutions. All on Topic 7A: Mass spectrometry I.
A sample of an unknown organic compound is analyzed using infrared (IR) spectroscopy. A broad absorption band is observed in the region \(3230\text{--}3550\text{ cm}^{-1}\). Which of the following functional groups is most likely present in the molecule?
An organic compound is analysed using infrared (IR) spectroscopy. The spectrum shows a strong, broad absorption peak in the range \(2500\text{--}3300 \text{ cm}^{-1}\) and another strong, sharp absorption peak at approximately \(1710 \text{ cm}^{-1}\). Which functional group is most likely present in the compound?
The mass spectrum of 2-chloropropane, \(\text{CH}_3\text{CHClCH}_3\), shows two molecular ion peaks at \(m/z = 78\) and \(m/z = 80\). What is the approximate ratio of the heights of the peak at \(m/z = 78\) to the peak at \(m/z = 80\)?
A compound has the molecular formula \(\text{C}_3\text{H}_6\text{O}_2\). Its infrared spectrum shows a broad absorption peak in the range \(2500\text{--}3300 \text{ cm}^{-1}\) and a strong peak at \(1710 \text{ cm}^{-1}\). In its mass spectrum, a prominent fragment peak is observed at \(m/z = 45\).
Which of the following ions is most likely responsible for the peak at \(m/z = 45\)?
The infrared spectrum of an unknown organic liquid shows a very broad absorption in the region \(3230\text{--}3550 \text{ cm}^{-1}\). When this liquid is reacted with acidified potassium dichromate(VI) and heated under reflux, the resulting product shows a broad absorption in the region \(2500\text{--}3300 \text{ cm}^{-1}\) and a new sharp peak at \(1705 \text{ cm}^{-1}\).
Which of the following could be the unknown organic liquid?
Identify the functional group present in an organic compound that shows a broad absorption band in the range \(2500-3300\text{ cm}^{-1}\) and a sharp peak at \(1710\text{ cm}^{-1}\) in its infrared spectrum.
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An organic compound contains only carbon, hydrogen, and oxygen. Mass spectrometry of the compound shows a molecular ion peak at \(m/z = 46\). Its infrared spectrum displays a strong, broad absorption at \(3350\text{ cm}^{-1}\) and a strong absorption at \(1050\text{ cm}^{-1}\), but no absorption between \(1680\text{ cm}^{-1}\) and \(1750\text{ cm}^{-1}\). Suggest the structural formula of the compound and justify your answer using both sets of analytical data.
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An unknown organic compound X contains only carbon, hydrogen, and oxygen. X has a molar mass of \(58.0\text{ g mol}^{-1}\).
(a) In the mass spectrum of X, a significant peak is observed at \(m/z = 29\). Suggest the formula of a possible fragment ion responsible for this peak. (1 point)
(b) The infrared (IR) spectrum of X shows a strong, sharp absorption at \(1715\text{ cm}^{-1}\) and no broad absorption between \(3200\) and \(3700\text{ cm}^{-1}\). Identify the functional group present in X and justify your answer based on these data. (2 points)
(c) Using the information from parts (a) and (b), and the fact that X has a molar mass of \(58.0\text{ g mol}^{-1}\), deduce two possible structural formulae for X. (2 points)
(d) A student suggests that X could be propanal. Describe a simple chemical test, including the observation for a positive result, that would distinguish propanal from the other isomer identified in part (c). (2 points)
Write your answer out first, then check it against the worked solution.
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