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Molecule V contains only carbon atoms, hydrogen atoms and one oxygen atom - VCE - SSCE Chemistry - Question 7 - 2023 - Paper 1
Question 7
Molecule V contains only carbon atoms, hydrogen atoms and one oxygen atom. The mass spectrum of molecule V is shown below. i. State the molecular formula of molecul... show full transcript
Worked Solution & Example Answer:Molecule V contains only carbon atoms, hydrogen atoms and one oxygen atom - VCE - SSCE Chemistry - Question 7 - 2023 - Paper 1
Step 1
i. State the molecular formula of molecule V. Justify your answer by using the information in the mass spectrum.
Answer
The molecular formula of molecule V is C₅H₈O.
This conclusion is drawn from the mass spectrum where the parent ion is located at m/z = 86. The molar mass indicates that the molecule contains 5 carbon atoms, 8 hydrogen atoms, and 1 oxygen atom, consistent with the total mass of 86 g/mol. The presence of various smaller peaks in the spectrum can also suggest the presence of different isotopes or fragments supporting this molecular composition.
Step 2
ii. State why there is a small peak at m/z = 87.
Answer
The small peak at m/z = 87 corresponds to the presence of the C-13 isotope in the molecule. This isotopic peak occurs due to the natural abundance of the C-13 isotope, which is about 1.1% of all carbon, resulting in a slight increase in mass for certain molecular ions.