State what is meant by the term acid deposition.

Identify one oxide which causes acid deposit

One effect of acid deposition is to decrease the pH of lake water. Suggest how this effect could be reversed.

acidic/acid-forming pollutants deposited on the Earth’s surface/leave the

atmosphere / rain/precipitation/deposition that is acidic/with a \({\text{pH}} < 5.6\);

Award mark if two specific examples are given.

\({\text{S}}{{\text{O}}_{\text{2}}}{\text{/S}}{{\text{O}}_{\text{3}}}{\text{/N}}{{\text{O}}_{\text{2}}}\);

Allow names of oxides. Do not allow NO_x.

Accept NO, but for second mark 2NO + O₂ \( \to \) 2NO₂ must also be included.

\({\text{S}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_3}/{\text{S}}{{\text{O}}_3} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_2}{\text{S}}{{\text{O}}_4}/\)

\({\text{2S}}{{\text{O}}_2} + {{\text{O}}_2} + {\text{2}}{{\text{H}}_2}{\text{O}} \to {\text{2}}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}/{\text{2N}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}} \to {\text{HN}}{{\text{O}}_2} + {\text{HN}}{{\text{O}}_3}/\)

\({\text{4N}}{{\text{O}}_2} + {{\text{O}}_2} + {\text{2}}{{\text{H}}_2}{\text{O}} \to {\text{4HN}}{{\text{O}}_3}\);

Do not allow ECF for equation.

addition of lime/Ca(OH)₂/limestone/CaCO₃;

Accept “adding alkali/base” or “neutralizing acidity”.

Though the precise definition of “acid deposition” was rarely encountered, most candidates managed a reply that gained them the mark. Even the simple equations required for the reaction of the oxide with water proved difficult for many candidates and, even though most knew how to counteract lake acidity, a disappointing number of students failed to link their method of reducing emissions to the oxide selected, for example mentioning catalytic converters in reference to oxides of sulfur.

Though the precise definition of “acid deposition” was rarely encountered, most candidates managed a reply that gained them the mark. Even the simple equations required for the reaction of the oxide with water proved difficult for many candidates and, even though most knew how to counteract lake acidity, a disappointing number of students failed to link their method of reducing emissions to the oxide selected, for example mentioning catalytic converters in reference to oxides of sulfur.

Though the precise definition of “acid deposition” was rarely encountered, most candidates managed a reply that gained them the mark. Even the simple equations required for the reaction of the oxide with water proved difficult for many candidates and, even though most knew how to counteract lake acidity, a disappointing number of students failed to link their method of reducing emissions to the oxide selected, for example mentioning catalytic converters in reference to oxides of sulfur.