Effects of Acid Deposition (DP IB Chemistry: HL)

Effect on materials

• Acid deposition can react with metals and rocks (such as limestone) causing buildings and statues to get damaged

The impact of acid deposition can be seen on buildings, statues and metallic structures, particularly in polluted cities

• Limestone and marble both contain calcium carbonate
• The calcium carbonate reacts with sulfuric or nitric acids causing stonework to corrode and weaken:

CaCO₃ (s)  + H₂SO₄ (aq)  →  CaSO₄ (aq)  +  CO₂ (g)  +  H₂O (l)

CaCO₃ (s)  + 2HNO₃ (aq)  →  Ca(NO₃)₂(aq)  +  CO₂ (g)  +  H₂O (l)

• In addition dry deposition also affects limestone:

CaCO₃ (s)  + H₂SO₄ (aq)  →  CaSO₄ (aq)  +  CO₂ (g)  +  H₂O (l)

• Metallic structures, such as iron bridges, are vulnerable to corrosion by wet and dry deposition forming the salt of the metal:

Fe (s)  + H₂SO₄ (aq) →  FeSO₄ (aq)  +  H₂ (g)

Fe (s)  + SO₂ (g)  + O₂ (g) →  FeSO₄ (s) 

Effect on plants

• Apart from acid deposition directly falling on leaves and killing plants, acid particulates can block stomata ( plant pores) and prevent gaseous exchange

The impact of acid deposition on plant life

• Acid rain can fall on soils and release important minerals such as magnesium, calcium and potassium which are leached (washed out) from soils and are therefore unavailable to plants
• Aluminium ions released from rocks are toxic to many plants and damage their roots

Effect on water

• When acid rain falls on rivers and lakes the pH can fall to levels that are unable to support life

The impact of acid deposition on waterways

• Below about pH 4, aluminium ions are released from rocks when they are held as aluminium hydroxide

Al(OH)₃ (s) + 3H⁺ (aq) →  Al³⁺ (aq)  + 3H₂O (l)

• Alumnium ions are toxic to fish as they damage the gills and prevent fish from efficiently absorbing oxygen
• Nitrate ions from nitric acid in acid rain can contibute to over-fertilization of waterways and lead to eutrophication
  • Eutrophication is excessive algal growth that results in oxygen depletion and stagnation of waterways

Effect on human health

• Although acid rain is too dilute to cause any direct impact on the skin, acidic particulates in the air can increase the risk of respiratory diseases such as bronchitis, asthma and emphysema
• When acid rain comes into contact with metal pipes there is an increased risk that toxic metal ions will be released into the water supply such as Cu²⁺, Al³⁺ and Pb²⁺