| Date | November 2013 | Marks available | 2 | Reference code | 13N.3.sl.TZ0.17 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 17 | Adapted from | N/A |
Question
The normal pH of rainwater is 5.6, but in some parts of the world rainwater has been recorded with a pH of several units lower than this. This is associated with harmful effects on living and non-living things.
The decrease in the pH of rainwater is mainly caused by oxides of non-metals, principally nitrogen and sulfur. State chemical equations that show how the primary pollutant nitrogen(II) oxide can produce two different acids containing nitrogen.
Explain, including an equation, the effect of the acid rain produced in (a) on certain stone buildings.
Markscheme
\({\text{2NO(g)}} + {{\text{O}}_{\text{2}}}{\text{(g)}} \to {\text{2N}}{{\text{O}}_{\text{2}}}{\text{(g)}}\);
\({\text{2N}}{{\text{O}}_2}{\text{(g)}} + {{\text{H}}_2}{\text{O(l)}} \to {\text{HN}}{{\text{O}}_2}{\text{(aq)}} + {\text{HN}}{{\text{O}}_3}{\text{(aq)}}\);
Ignore state symbols.
Award [1 max] for 4NO2(aq) + 2H2O(l) + O2(g) \( \to \) 4HNO3(aq).
erosion / buildings of marble/limestone;
\({\text{2HN}}{{\text{O}}_3}{\text{(aq)}} + {\text{CaC}}{{\text{O}}_3}{\text{(s)}} \to {\text{Ca(N}}{{\text{O}}_3}{{\text{)}}_2}{\text{(aq)}} + {{\text{H}}_2}{\text{O(l)}} + {\text{C}}{{\text{O}}_2}{\text{(g)}}\) /
\({\text{2HN}}{{\text{O}}_2}{\text{(aq)}} + {\text{CaC}}{{\text{O}}_3}{\text{(s)}} \to {\text{Ca(N}}{{\text{O}}_2}{{\text{)}}_2}{\text{(aq)}} + {{\text{H}}_2}{\text{O(l)}} + {\text{C}}{{\text{O}}_2}{\text{(g)}}\);
Ignore state symbols.
Examiners report
This question was not done well. Few candidates were able to form the two different nitrogen containing acids and the acid used in (b) was generally sulfuric!
This question was not done well. Few candidates were able to form the two different nitrogen containing acids and the acid used in (b) was generally sulfuric!
