Reactions
2H + MgO - Mg2+ + H2O
2H + Mg(OH)2.- Mg2+ + H2O
2H + Ca(OH)2 - Ça2+ + H2O
Which is he best base to use?
Both the compounds containing magnesium react to produce magnesium sulfate, which is soluble and may affect water quality. Calcium hydroxide is soluble and also may affect the surrounding water and decreases effectiveness because the calcium hydroxide may be washed away before neutralising the soil. Calcium carbonate is the best base to use because it is insoluble, therefore it is least likely to affect surrounding water and will treat the soil more slowly and gradually because it will dissolve over a period of time.

Disadvantages of soil treatment using bases
Not natural process
Requires energy, labour and heat intensive processes to manufacture and transport the substances
Temporary solution only, usually will have to be repeated
Produces carbon dioxide and salt precipitates when reacting that could harm the environment

Why rain is naturally acidic:
Unpolluted rainwater has a pH of around 5.6
Gases in the atmosphere where rain forms react with water to form acids
H2O + CO2 - H2CO3 (carbon dioxide reacts with water to form carbonic acid) NO - NO2 + H2O - HNO3 (nitric oxide is oxidised in air to form nitrogen dioxide then reacts with water to form nitric acid)
SO2 + H2O - H2SO4 (sulfur dioxide reacts with water to form sulfuric acid) Describe what is meant by acid rain:
Rainfall that has become more acidic (classified by a pH below 5) as a result of air pollution
Human activities involving fuel combustion produce emissions, including nitrogen oxide and sulfur dioxide, which increases the atmospheric levels of these gases and consequently the acid concentration of the rainwater
Main source is fuel combustion in power plants to produce electricity
Also emitted from car exhausts

How does acid rain impact the environment?
Enters surface water (lakes, streams etc.) and lowers the pH
Some aquatic species