A bottle containing an unknown organic compound was examined in a university laboratory - VCE - SSCE Chemistry - Question 4 - 2016 - Paper 1
Question 4
A bottle containing an unknown organic compound was examined in a university laboratory. There was an incomplete label on the bottle that gave only the empirical for... show full transcript
Worked Solution & Example Answer:A bottle containing an unknown organic compound was examined in a university laboratory - VCE - SSCE Chemistry - Question 4 - 2016 - Paper 1
Step 1
i. On the diagram above, circle the base peak.
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Answer
The base peak is the tallest peak on the mass spectrum, corresponding to the most abundant species. In this case, it appears at m/z = 30.
Step 2
ii. At what m/z ratio is the principal peak that supports the chemist's hypothesis that the unknown compound has the formula NH₂CH₂CH₂NH₂? Justify your answer.
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Answer
The principal peak appears at m/z = 60. This supports the hypothesis because the molecular mass of NH₂CH₂CH₂NH₂ is calculated as follows:
Nitrogen (N): 14 g/mol × 2 = 28 g/mol
Carbon (C): 12 g/mol × 2 = 24 g/mol
Hydrogen (H): 1 g/mol × 8 = 8 g/mol
Adding these together: 28 + 24 + 8 = 60 g/mol.
Step 3
iii. Write the semi-structural formula of the species that produces the peak at 30 m/z.
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Answer
The semi-structural formula for the species that produces the peak at 30 m/z is H₂NCH₂CH₂^+.
