One of the properties of limestone is that it reacts with acids.
(i) Why do farmers spread powdered limestone on their fields?
(ii) How can buildings made of limestone be affected by ‘acid rain’?
(iii) Write an ionic equation which would represent the reactions taking place in both
(i) and (ii).
The primary use of ag lime is to raise the pH of acid soils and reduce the concentration of aluminum (Al) in soil solution. Poor crop growth in acid soils largely results from too much soluble Al, which is toxic to the root system of many plants.
Acid deposition also affects human-made structures. Sulfur dioxide, an acid rain precursor, can react directly with limestone in the presence of water to form gypsum, which eventually flakes off or is dissolved by water. In addition, acid rain can dissolve limestone and marble through direct contact.
The sulfuric acid then further reacts with the limestone in a neutralization reaction.
aCO3 + H2SO4 --> CaSO4 + H2CO3
H2CO3 --> CO2 gas + H2O
The calcium sulfate is soluble in water and hence the limestone dissolves and crumbles.