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Date November 2016 Marks available 2 Reference code 16N.3.sl.TZ0.13
Level SL Paper 3 Time zone TZ0
Command term Explain Question number 13 Adapted from N/A

Question

Carbon dioxide and water vapour are greenhouse gases produced by the combustion of fossil fuels.

Explain the effect of the increasing concentration of atmospheric carbon dioxide on the acidity of oceans.

[2]
a.

(i) Describe the changes that occur at the molecular level when atmospheric carbon dioxide gas absorbs infrared radiation emitted from the Earth’s surface.

(ii) Other than changes to the acidity of oceans, suggest why the production of carbon dioxide is of greater concern than the production of water vapour.

[3]
b.

Markscheme

Any two of:

CO(g) \(\mathop  \rightleftharpoons \limits^{{{\text{H}}_{\text{2}}}{\text{O}}\,{\text{(l)}}} \) CO(aq)  

CO(aq) + H2O (l) \( \rightleftharpoons \) H+ (aq) + HCO3 (aq)
OR
HCO3 AND H+ are formed «by dissolved CO2»

«increasing [CO2]» shifts equilibrium to right/increases acidity/decreases pH

H2O (l) not required over equilibrium sign for M1.

State symbols required in the equation in M1.

Accept “H2CO3 ” at either side of the equilibrium in M2.

Equilibrium sign required for M1 but not for M2.

a.

i

bond length/C=O changes
OR
«asymmetric» stretching «of bonds»
OR
bond angle/OCO changes

Accept “molecule bends” for M1.
Accept appropriate diagrams

photon re-emitted in random direction
OR
polarity/dipole «moment» changes
OR
dipole «moment» created «when molecule absorbs IR» 

 

ii

CO2 gas «ten times» more effective as greenhouse gas/GHG than H2O
OR
CO2 gas levels keep increasing «unlike H2
OR
CO2 has higher Global Warming Potential/GWP than H2O
OR
CO2 stays in the atmosphere for longer than H2

Accept converse arguments.

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Options » C: Energy » C.5 Environmental impact—global warming
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