Work through these eight questions in order. They cover all four lessons in carbon compounds.
The timed practice session builder can turn the set into a timed run.
Questions
Question 1 (2 marks). Classify C5H12 and C5H10. Use the general formulae.
Answer
C5H12: n = 5, 2n + 2 = 12, so it is an alkane. C5H10: 2n = 10, so it is an alkene.
Question 2 (1 mark). State the functional group in C2H5OH.
Answer
The -OH group, so the compound is an alcohol.
Question 3 (2 marks). Describe what you see when ethene is shaken with brown bromine water.
Answer
The brown colour of the bromine water changes to colourless, because ethene is unsaturated and reacts with bromine.
Question 4 (2 marks). Explain why ethane causes no change to bromine water.
Answer
Ethane is saturated and has only single carbon-carbon bonds, so it does not add bromine and the brown colour stays.
Question 5 (3 marks). Calculate the percentage of carbon by mass in propene, C3H6. C = 12, H = 1.
Answer
Mass of the molecule = 3(12) + 6(1) = 42. Carbon = 36. Percentage = 36 ÷ 42 × 100 = 85.7%.
Question 6 (2 marks). Explain how ethene molecules form poly(ethene).
Answer
The carbon-carbon double bond in each ethene molecule opens, and the molecules join one after another into a long chain. Ethene is the monomer and poly(ethene) is the polymer.
Question 7 (3 marks). Fuel X releases 45 kJ per gram and Fuel Y releases 36 kJ per gram. Find the mass of each needed to release 360 kJ.
Answer
Fuel X: 360 ÷ 45 = 8 g. Fuel Y: 360 ÷ 36 = 10 g.
Check: 8 × 45 = 360 and 10 × 36 = 360.
Question 8 (4 marks). In a model, photosynthesis removes 100 units of carbon dioxide from the air and respiration, decomposition and combustion add 50, 30 and 25 units. Find the net change and state one assumption.
Answer
Added: 50 + 30 + 25 = 105. Net = 105 − 100 = +5 units, so carbon dioxide in the air rises by 5 units.
Assumption: only these four flows are counted, over the same period.
If you got these wrong
Formula slips in questions 1 and 2: revisit recognising basic carbon-compound groups. For questions 3 to 5, see comparing saturated and unsaturated compounds. For 6 and 7, go to explaining polymer and fuel applications. For 8, see interpreting carbon-cycle information.
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