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Date	November 2017	Marks available	3	Reference code	17N.3.sl.TZ0.13
Level	SL	Paper	3	Time zone	TZ0
Command term	Explain	Question number	13	Adapted from	N/A

Question

Much of our energy needs are still provided by the refined products of crude oil.

“Knocking” in an automobile (car) engine can be prevented by increasing the octane number of the fuel. Explain, including an equation with structural formulas, how heptane, C₇H₁₆, could be chemically converted to increase its octane number.

[3]

Many like to refer to our “carbon footprint”. Outline one difficulty in quantifying such a concept.

[1]

Climate change or global warming is a consequence of increased levels of carbon dioxide in the atmosphere. Explain how the greenhouse effect warms the surface of the earth.

[3]

Outline how water and carbon dioxide absorb infrared radiation.

[1]

Markscheme

CH₃CH₂CH₂CH₂CH₂CH₂CH₃ → CH₃CH(CH₃)CH₂CH(CH₃)₂

CH₃CH₂CH₂CH₂CH₂CH₂CH₃ →

isomerisation/reforming/platforming/cracking

Pt/Re/Rh/Pd/Ir

catalyst

A structural formula is only required for the organic product, not heptane.

Accept any correctly balanced equation showing increased branching or cyclization OR aromatization OR cracking.

Suitable supports for catalysts may be included for M3 (eg silica, alumina, zeolite) but the symbol or name of an appropriate metal must be given (typically a noble metal). Ignore temperature and other conditions.

Award M2 AND M3 for “catalytic isomerisation” OR “catalytic reforming” OR “catalytic cracking”.

which specific carbon-based greenhouse gases are included

whether non-carbon based greenhouse gases should be included

whether CO/incomplete combustion should be included «as can be oxidized to CO₂»

how to “sum” all steps in a process creating CO₂

difficult to determine both direct and indirect production of GHG/greenhouse gas emissions

Ignore reference to geopolitical issues (eg false recording of data by governments etc.).

Accept “difficult to measure all sources of CO₂” but not “difficult to measure CO₂ released in atmosphere”.

Any three of:

incoming solar radiation is short wavelength/high frequency/high energy/UV

radiated/emitted as long wavelength/low frequency/low energy/IR «radiation»

energy/IR «radiation» absorbed by «bonds in» greenhouse gases