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

(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.

Any two of:

CO₂ (g) \(\mathop  \rightleftharpoons \limits^{{{\text{H}}_{\text{2}}}{\text{O}}\,{\text{(l)}}} \) CO₂ (aq)  

CO₂ (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.

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 H₂O»
OR
CO₂ has higher Global Warming Potential/GWP than H₂O
OR
CO₂ stays in the atmosphere for longer than H₂O 

Accept converse arguments.