Answer Happy

8.14 pH and acid rain. Although rainwater is in itself slightly acidic (with a pH between 5 and 6), whenever the pH is below 5 the rain is considered to be acidic, and hence detrimental to the environment. The causes of acid rain are mostly emissions from coal-fired power plants, vehicles, and other chemical pollutants, but also from volcanic eruptions. The substance of most concern is sulfur dioxide (SO₂). The reaction that occurs in the atmosphere is the following: 2(SO₂) + 0₂ 2SO3 followed by SO3 + H₂O H₂SO4. Sulfuric acid in water produces hydrogen cations and SO4 anions: H₂SO4 → 2H+ + SO²¯. To understand the problem of acid rain, consider an atmospheric con- centration of 2 ppm SO₂ (this is a large concentration not likely to occur except locally during volcanic eruptions or in extremely polluted regions). Assuming that 0.75 ppm SO₂ is absorbed by falling rain that in the absence of SO₂ in the atmosphere would have a pH of 5.8, what is the pH of the rainwater after absorption of SO₂?