O-LevelChemistryOrganic Chemistry5070/21 · May/June 2018 · Q910 Marks

Methylpropane is a saturated hydrocarbon. [Figure showing structure of methylpropane] H H H | | | H—C—C—C—H | | | H H H | H—C—H | H methylpropane

(a)(i)Methylpropane reacts with chlorine in the presence of ultraviolet light to give several compounds. One of these compounds has a relative molecular mass of 127. What is the molecular formula of this compound? molecular formula Suggest a structure for this compound. Show all of the atoms and all of the bonds.[2]
(a)(ii)Another compound formed has the percentage composition by mass: 29.7% carbon; 4.3% hydrogen; 65.9% chlorine. Calculate the molecular formula for this compound. molecular formula[2]
(a)(iii)A compound is formed when one molecule of methylpropane reacts with five molecules of chlorine. Write the molecular formula for this compound.[1]
(b)(i)The structures of propene and cyclopropane are shown. H H | | H—C=C—C—H | | | H H H propene H H / \ C H H | | C—C | | H H cyclopropane These two compounds are isomers of each other. What is meant by the term isomerism?[1]
(b)(ii)Both compounds are hydrocarbons. What is meant by the term hydrocarbons?[1]
(b)(iii)Propene is an unsaturated hydrocarbon and cyclopropane is a saturated hydrocarbon. What is the difference between an unsaturated and a saturated hydrocarbon?[1]
(b)(iv)Describe a chemical test to distinguish between unsaturated and saturated hydrocarbons.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[2] 9(a)(i) molecular formula is C4H8Cl2 (1) Structure showing all atoms and all of the bonds of a compound having two chlorine atoms substituted and based on methylpropane skeleton e.g. HHH HCIH H-C-C-C-H H-C-C-C-H Cl Cl Cl H H-C-H H H-C-H H (1)
[2] 9(a)(ii) molecular formula is C4H7Cl3 (2) If two marks not scored: 1 mark for mole ratio C: H: Cl is 2.475: 4.30: 1.856 OR 1 mark for C = 29.7/12, H = 4.3/1 and Cl = 65.9/35.5
[1] 9(a)(iii) C4H5C15 (1)
[1] 9(b)(i) same molecular formula but different structures / same molecular formula but different arrangement of atoms (1)
[1] 9(b)(ii) (compounds) containing only hydrogen and carbon (1)
[1] 9(b)(iii) unsaturated contains a carbon-carbon double bond / saturated does not contain carbon-carbon double bond (1)
[2] 9(b)(iv) add (aqueous) bromine (1) unsaturated goes colourless and saturated stays orange (1)

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.