Edexcel Jan 2015 (IAL) Paper 1 Q21 (with explained solutions) |

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Edexcel Jan 2015 (IAL) Paper 1 Q21

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Answer ALL the questions. Write your answers in the spaces provided. SECTION B 21 Crude oil is a source of alkanes. (a) Name the process by which the hydrocarbons in crude oil are separated. (1)(b) The alkane X is composed of straight-chain molecules, each with nine carbon atoms. (i) Give the molecular formula of X. (1)(ii) Y is a branched-chain isomer of X. Y has eight carbon atoms in a straight-chain with one methyl group as a side-chain. Skeletal formula: Name: Draw the skeletal formula of one possible structure for Y. Give the name of the structure that you have drawn. (2)10 *P45041A01024*<br />
(c) A reaction called cracking occurs when the alkane pentadecane, C15H32, is heated in the presence of a catalyst. (i) Give an equation to show the cracking of one molecule of C15H32 to form one molecule of ethene and a molecule of one other product. State symbols are not required. (ii) In practice, cracking pentadecane forms a large number of products. Suggest why this is so. (1) (1)(d) In the petroleum industry, some straight-chain alkanes are processed to form cyclic hydrocarbons. When octane is processed, each molecule of octane produces one molecule of a cyclic hydrocarbon, C8H12, and three molecules of hydrogen as the only products. (i) Complete the skeletal formula of one of the possible cyclic hydrocarbons. (ii) Suggest why the petroleum industry processes straight-chain alkanes to form cyclic hydrocarbons. (1) (1)(Total for Question 21 = 8 marks) *P45041A01124* 11 Turn over<br />

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Section B Question Number 21(a) Question Number 21(b)(i) Acceptable Answers Fractional distillation Both words needed Acceptable Answers C9H20 Question Number 21(b)(ii) Correct skeletal formula (1) Acceptable Answers Correct name for the structure drawn providing that the structure is a branched-chain isomer of C9H20 NO TE for name if skeletal formula is incorrect ALLOW Correct name, even if structural or displayed formula has been drawn (1) EXAMPLES of correct skeletal formulae and names 2-methyloctane 3-methyloctane 4-methyloctane Reject Reject Reject Structural or displayed formula Mark Mark Mark WCH0101 1501<br />
Acceptable Answers Question Number 21(c)(i) can break OR The carbon chain can break/split in different places OR Carbon chain is cracked in many places / different places OR C13H28 / product will break down further IGNORE Molecule can break anywhere / It breaks into smaller molecules / large number of C atoms / bonds break randomly / hydrocarbon chain is long C15H32C13H28 + C2H4 IGNORE State symbols, even if incorrect ALLOW Correct structural OR displayed OR skeletal OR mixture of these (as long as unambiguous) Question Number 21(c)(ii) Any carbon-carbon bond (in the chain) Acceptable Answers Reject Mark Reject Mark WCH0101 1501<br />
Question Number 21(d)(i) Acceptable Answers Reject Mark Two double bonds anywhere on the RING (allow them to be adjacent). e.g. ALLOW One triple bond (instead of two double bonds) BUT not adjacent to a methyl group ALLOW: (ie double bond(s) on side-chain) If any other incorrect structure is included with the final answer Any 5-valent C atom in structure scores (0) If the methyl groups are joined by a bond (0) Benzene ring (0) WCH0101 1501<br />
Question Number 21(d)(ii) NOTE Acceptable Answers The answer must relate to combustion or burning To promote efficient combustion OR To increase octane number OR To reduce knocking OR Pre-ignition less likely ALLOW To allow smoother burning OR More efficient fuels OR Better burning / fuels easier to burn OR Combust more easily OR Improves combustion ALLOW Reverse argument for straight-chain hydrocarbons IGNORE References to: less pollution / burning more cleanly / better fuels / to form alkenes / to form more useful products /branched chains form / boiling point / volatility / to form H2 Mark Reject Ignition less likely (0) (Total for Question 21 = 8 marks) WCH0101 1501<br />

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