topic 8.5 - acid deposition

Question 1

Acid rain

Answer 1

Natural water has a pH of 7
Rainwater has a pH of 5.6 due to the presence of dissolved carbon dioxide that forms carbonic acid (a weak acid) - H₂CO₃ (g)

Question 2

Acid deposition - Sulfur dioxide

Sulfur dioixde -> sulfurous acid -> bisulfite

Sulfur dioxide -> sulfur trioxide -> sulfuric acid

Answer 2

Sulfur dioxide is produced from volcanoes, burning fossil fuels, and vegetation decomposition.

S (s) + O₂ (g) -> SO₂ (g)

Sulfur dioxide combines with water to form sulfurous acid:
SO₂ (g) + H₂O (l) ⇌ H₂SO₃ (aq)
H₂SO₃ (aq) + H₂O (l) ⇌ HSO₃⁻ (aq) + H₃O⁺ (aq)

Sulfur trioxide can be formed and form sulfuric acid:
2SO₂ (g) + O₂ (g) -> 2SO₃ (g)
SO₃ (g) + H₂O (l) -> H₂SO₄ (aq)

Question 3

Acid deposition - nitrogen oxides

Nitrogen -> nitrogen (II) oxide -> nitrogen (IV) oxide

Nitrogen (IV) oxide -> nitric acid

Nitrous acid -> nitric acid

Answer 3

Nitrogen oxides are produced at high temperatures inside internal combustion engines such as those found in jets or cars.

Nitrogen reacts with oxygen to form a nitrous oxide:
N₂ (g) + O₂ (g) -> 2NO (g)
2NO (g) + O₂ (g) -> 2NO₂ (g)

Nitrogen (IV) oxide reacts with water to form nitric acid:

2NO₂ (g) + H₂O (l) -> HNO₃ (aq) + HNO₂ (aq)

Nitrous acid reacts with oxygen to form nitric acid:

2HNO₂ (aq) + O₂ (g) -> 2HNO₃ (g)

Question 4

Pre-combustion technology

Answer 4

Crushing then floating coal can cause impurities such as sulfur to be removed and these various methods of reducing impurities can cause the removal of 80-90% of sulfur and therefore reduce sulfur emissions from fossil fuels.

Question 5

Post-combustion technology

Answer 5

Lining exhaust pipes with calcium oxide or other substances can remove harmful substances.