This set has twelve original questions, ordered from easier to harder, covering all five lessons in organic families and naming. Questions 1 to 4 check recognition, 5 to 8 check bonding and formulae, and 9 to 12 mix skills.
Attempt each question on paper before you open the answer. Draw structures as displayed formulae where asked, and write the working you would show in an exam. Then mark any error by type and use the routing list at the end.
The data in the questions are invented for practice. Check the current 0620 syllabus on the Cambridge page for which families and names your exam year includes.
Questions
1. Name the functional group in CH₃CH₂CH₂CH₂OH, the family it belongs to and its name.
Show answer
The molecule has an -OH on a carbon with only single bonds and no C=O, so the group is -OH and the family is alcohol. There are four carbons, so the name is butanol (butan-1-ol if the position is written).
2. Name the functional group and the family of CH₃CH₂CH₂COOH, and give its name.
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The group is -COOH, so the family is carboxylic acid. The carboxyl carbon counts as the fourth carbon (CH₃, CH₂, CH₂ and COOH), so the name is butanoic acid.
3. Write the molecular formula of the alkane and of the alkene that each have seven carbons.
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Alkane: CₙH₂ₙ₊₂ with n = 7 gives 2(7) + 2 = 16, so C₇H₁₆. Alkene: CₙH₂ₙ gives 2(7) = 14, so C₇H₁₄. The alkene has two fewer hydrogens because of the C=C double bond.
4. Are CH₄ and C₃H₈ in the same homologous series? Explain.
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Yes. Both are alkanes with only single bonds. The formulae differ by C₂H₄, which is two CH₂ units, so they are members of the same homologous series, though not neighbouring ones.
5. A student draws a carbon atom with one C=O double bond, one single bond to an oxygen atom and one single bond to another carbon atom. A second carbon drawn beside it has a double bond and three C-H bonds. Which carbon is drawn wrongly, and why?
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First carbon: double bond counts 2, plus 1 and 1 gives 4 bonds, which is correct. Second carbon: the double bond counts 2 and three C-H bonds count 3, giving 5 bonds, so the second carbon is wrong. A carbon forms only four bonds, so one C-H bond must go.
6. Draw the displayed formula of propane, C₃H₈, and count the covalent bonds.
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H H H
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H - C - C - C - H
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H H HEach carbon has four bonds. There are 2 C-C bonds and 8 C-H bonds, so 10 bonds in total.
7. Which pair are isomers? A: butane and methylpropane. B: ethanol and ethene. C: pentane and hexane.
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Pair A. Butane is CH₃CH₂CH₂CH₃, C₄H₁₀, and methylpropane is CH₃CH(CH₃)CH₃, also C₄H₁₀, with a different arrangement. A is the isomer pair. B is C₂H₆O and C₂H₄, different formulae. C is C₅H₁₂ and C₆H₁₄, which are members of the same series and not isomers.
8. For CH₃CH=CHCH₃, state the molecular formula, whether it is saturated and the family.
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Carbons: 4. Hydrogens: 3 + 1 + 1 + 3 = 8. The molecular formula is C₄H₈. It contains a C=C, so it is unsaturated and is an alkene (but-2-ene). It fits CₙH₂ₙ for n = 4.
9. Two colourless gases X and Y are known to be C₃H₆ and C₃H₈, but the labels are lost. X decolourises bromine water and Y does not. Which is which, and why?
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X is C₃H₆ and Y is C₃H₈. Decolourising bromine water is the result for an unsaturated compound with a C=C. C₃H₆ has two fewer hydrogens than the saturated C₃H₈ (2n + 2 = 8), so it is the alkene, propene.
10. Write the molecular formula and name of CH₃CH₂CH₂CH₂COOH.
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Carbons: 4 in the chain plus the carboxyl carbon gives 5. Hydrogens: 3 + 2 + 2 + 2 + 1 = 10. Oxygens: 2. The molecular formula is C₅H₁₀O₂ and the name is pentanoic acid.
11. A student says ethanol and ethanoic acid are isomers because both have two carbons and an -OH. Correct the statement.
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Ethanol is C₂H₆O and ethanoic acid is C₂H₄O₂, so the molecular formulae differ and they cannot be isomers. They are also in different families: ethanol is an alcohol (-OH) and ethanoic acid is a carboxylic acid (-COOH, with a C=O on the same carbon as the -OH).
12. A compound has molecular formula C₄H₈O₂ and contains a -COOH group. Write two possible structural formulae and say how they are related.
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One structure is CH₃CH₂CH₂COOH (butanoic acid): C = 4, H = 3 + 2 + 2 + 1 = 8, O = 2. A second is CH₃CH(CH₃)COOH (methylpropanoic acid): C = 4, H = 3 + 1 + 3 + 1 = 8, O = 2. Both are C₄H₈O₂ with different structures, so they are isomers, and both are carboxylic acids.
If you got these wrong
Mark each error by type, then go back to the matching lesson.
- Questions 1 and 2, or confusing -OH with -COOH: return to identifying a functional group.
- Questions 4, 7 and 11, or mixing up series and isomers: return to distinguishing homologous family from isomer.
- Questions 5 and 6, or bond counts that do not add up: return to drawing a small molecule with correct bonding.
- Questions 3, 8 and 9, or mistakes about saturated and unsaturated: return to recognising saturated and unsaturated structures.
- Questions 10 and 12, or wrong hydrogen counts: return to converting between formula representations.
The mistake log and retest queue can hold each error with a fresh question to retry later. The equation balance reasoning trainer and mole and equation-ratio tutor help when formulae feed into equations and calculations.
When you finish, continue to organic reactions. If one error type keeps returning, online one-to-one Chemistry tuition lets a teacher read your working and find the pattern with you.