Topic 8.5: Acid deposition

Question 1

Definition of acid deposition

Answer 1

Process by which acid forming pollutants are deposited on the Earth’s surface

Question 2

What is the natural pH of rain? Why does it have that pH?

Answer 2

Rain is naturally acidic due to dissolved CO2 and has a pH of 5.6

Question 3

What is the pH of acid deposition? How is it formed?

Answer 3

a) It has a pH below 5.6

b) Acid deposition occurs when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3.

Question 4

What are the sources of sulfur oxides? (2)

Answer 4

a) Extracting metals from their ores

b) Burning of fossil fuels (e.g., coal / heavy oil)

Question 5

Chemical equation for the formation of sulfur oxides from combustion reactions (2)

Answer 5

a) S(s) + O2(g) => SO2(g)

b) 2SO2(g) + 02(g) => 2SO3(g)

Question 6

Chemical equation for the dissolution of sulfur oxides in water (2)

Answer 6

a) H2O(l) + SO2(g) => H2SO3(aq)

b) H2O(l) + SO3(g) => H2SO4(aq)

Question 7

What is the source of nitrogen oxide?

Answer 7

Internal combustion engines

Question 8

Chemical equation for the formation of nitrogen oxides from combustion reactions (2)

Answer 8

a) N2(g) + O2(g) => 2NO(g)

b) 2NO(g) + O2(g) => 2NO2(g)

Question 9

Chemical equation for the dissolution of nitrogen oxides in water

Answer 9

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

Question 10

Effects of acid deposition (2)

Answer 10

a) Impact on materials

b) Impact on the environment / human health

Question 11

Impact on materials

Answer 11

a) Expansion and stress in stonework
b) Erosion of structures
c) Corrosion reaction (Rusting)

Question 12

Expansion and stress in stonework

a) Chemical equation for the reaction of SO2(g) and CaCO3(s)

Answer 12

2CaCO3(s) + 2SO2(g) + O2(g) => 2CaSO4(aq) + 2CO2(g)

Question 13

Erosion of structures

a) Chemical equation for the reaction of CaCO3 and H2SO4 / HNO3

Answer 13

a) CaCO3(s) + H2SO4(aq) => CaSO4(aq) + CO2(g) + H2O(l)

b) CaCO3(s) + 2HNO3(aq) => Ca(NO3)2 (aq) + C02(g) + H2O(l)

Question 14

Corrosion reaction

a) Chemical equation for the reaction of Fe and SO2

Answer 14

a) Fe(s) + SO2(g) + O2(g) => FeSO4(s)

Question 15

Corrosion reaction

a) Chemical equation for the reaction of Fe and H2SO4
b) Chemical equation for the reaction of Al2O3 and 6HNO3

Answer 15

a) Fe(s) + H2SO4(aq) => FeSO4(aq) + H2(g)

b) Al2O3(s) + 6HNO3(aq) => 2Al(NO3)3 + 3H2O(l)

Question 16

Impacts of acid deposition on environment (2)

Answer 16

a) Displaces metal ions from soil and prevents the growth / development of plants
b) Elevates acid levels in lakes and rivers, affect pH sensitive ecosystems

Question 17

Impacts of acid deposition on human health

Answer 17

a) Causes the poisoning of fish, eventually resulting in damage to human health
b) Irritates mucous membrane causing respiratory illness (asthma)

Question 18

Methods used to reduce SO2 emissions

Answer 18

a) Pre-combustion

b) Post-combustion

Question 19

Precombustion methods used to reduce SO2 emissions

Answer 19

Hydrodesulfurization (HDS) is a catalytic process that removes sulfur from refined petroleum products by reacting it with hydrogen to form H2S, which is used to manufacture H2SO4

Question 20

Postcombustion methods used to reduce SO2 emissions

Answer 20

Flue-gas desulfurization can remove up to 90% of SO2 from flue gas in the smokestacks of coal-fired power stations before it is released into the atmosphere