Physical properties
4 marks · NormalThe table below shows the number of carbon atoms and the molecular formula for three alkenes. For each, state if the formula is correct for an alkene. If not, explain your answer.
| Alkene | Number of C atoms | Molecular formula |
|---|---|---|
| W | 4 | C4H8 |
| X | 5 | C5H12 |
| Y | 3 | C3H6 |
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Common mistakes: Assuming all given are correct; Not explaining when formula doesn't fit
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Marking points
B1 · 1 mark · W: Identifies C4H8 is correct (fits CnH2n)
B2 · 1 mark · X: States C5H12 is incorrect for an alkene
B3 · 1 mark · X: Explains C5H12 does not fit CnH2n
B4 · 1 mark · Y: Identifies C3H6 is correct (fits CnH2n)
Worked solution
W: C4H8 – correct for alkene (C4H2×4 = C4H8).
X: C5H12 – incorrect for alkene, because 2×5 = 10. The correct alkene formula for 5C would be C5H10.
Y: C3H6 – correct for alkene (C3H2×3 = C3H6).