Acid deposition

Nature of science:

Risks and problems—oxides of metals and non-metals can be characterized by their acid–base properties. Acid deposition is a topic that can be discussed from different perspectives. Chemistry allows us to understand and to reduce the environmental impact of human activities. (4.8)

• Rain is naturally acidic because of dissolved CO₂ and has a pH of 5.6. Acid deposition has a pH below 5.6.
• Acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO₃, HNO₂, H2SO₄ and H₂SO₃.
• Sources of the oxides of sulfur and nitrogen and the effects of acid deposition should be covered.

Applications and skills:

• Balancing the equations that describe the combustion of sulfur and nitrogen to their oxides and the subsequent formation of H₂SO₃, H₂SO₄, HNO₂ and HNO₃.
• Distinction between the pre-combustion and post-combustion methods of reducing sulfur oxides emissions.
• Deduction of acid deposition equations for acid deposition with reactive metals and carbonates.

• The polluter country and polluted country are often not the same. Acid deposition is a secondary pollutant that affects regions far from the primary source. Solving this problem requires international cooperation.

Theory of knowledge:

• All rain is acidic but not all rain is “acid rain”. Scientific terms have a precise definition. Does scientific vocabulary simply communicate our knowledge in a neutral way or can it have value-laden terminology?

Utilization:

• Syllabus and cross-curricular links:
• Topic 3.2—the acid/base character of the oxides Option
• B.2—pH change and enzyme activity
• Option C.2—sulfur dioxide is produced by the combustion of fossil fuels with high levels of sulfur impurities
• Environmental systems and societies topic 5.8—acid deposition
• Geography Option G: Urban Environments—urban stress and the sustainable city; HL—Global interactions—environmental change

Aims:

• Aim 6: The effects of acid rain on different construction materials could be quantitatively investigated.
• Aim 8: A discussion of the impact of acid rain in different countries will help raise awareness of the environmental impact of this secondary pollutant and the political implications.
• Aim 8: Other means of reducing oxide production—bus use, car pooling, etc. could be discussed.