| Date | May 2009 | Marks available | 3 | Reference code | 09M.3.sl.TZ2.E1 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Outline | Question number | E1 | Adapted from | N/A |
Question
The exhaust gases of automobiles contribute significantly to air pollution in cities.
Outline how the pollutant gases nitrogen(II) oxide, NO, nitrogen(IV) oxide, \({\text{N}}{{\text{O}}_2}\) and carbon monoxide, CO, are formed as a result of the action of the internal combustion engine.
NO:
\({\text{N}}{{\text{O}}_2}\):
CO:
Markscheme
NO:
\({{\text{N}}_{\text{2}}}\) and \({{\text{O}}_{\text{2}}}\) react in the engine / \({{\text{N}}_{\text{2}}} + {{\text{O}}_{\text{2}}} \to {\text{2NO}}\);
No mark for the high temperature without reference to the action between N2 and O2.
\(N{O_2}\):
NO oxidizes/reacts in the air to \({\text{N}}{{\text{O}}_{\text{2}}}\) / x;
\({\text{2NO}} + {{\text{O}}_{\text{2}}} \to {\text{2N}}{{\text{O}}_{\text{2}}}\);
CO:
incomplete combustion;
Accept balanced chemical equation for C5–C12 hydrocarbons.
Do not accept C1–C4.
Examiners report
Many candidates identified correctly how the three gases are formed, though some candidates named the reaction of \({{\text{N}}_{\text{2}}}\) and \({{\text{O}}_{\text{2}}}\) as the source of \({\text{N}}{{\text{O}}_{\text{2}}}\) and for incomplete combustion equations with methane and carbon were given.
