Explain why the following are done, both of which are related to acid-base chemistry. a. Power plants burning coal with high sulfur content use scrubbers to help eliminate sulfur emissions. b. A gardener mixes lime \((\mathrm{CaO})\) into the soil of his garden.

Coal with high sulfur content produces sulfur dioxide (SO₂) and sulfur trioxide (SO₃) when burned, which are harmful to both the environment and human health. These sulfur compounds react with water in the atmosphere to form sulfuric acid (H₂SO₄), which can lead to acid rain, harming plants, aquatic life, and infrastructure. In order to prevent these negative effects, power plants use scrubbers, which help eliminate sulfur emissions from the exhaust gases. The scrubbers utilize a basic substance (often limestone, CaCO₃, or lime, CaO) that reacts with the acidic sulfur compounds, neutralizing them and forming mostly harmless byproducts. This process can be represented by the following reaction: \[SO_2 (g) + CaO (s) \rightarrow CaSO_3 (s)\] \[SO_3 (g) + CaO (s) \rightarrow CaSO_4 (s)\] Hence, scrubbers help reduce the environmental impact of sulfur emissions by neutralizing the harmful acidic compounds produced during the combustion of high-sulfur coal.

Soil acidity can negatively affect plants by limiting the availability of essential nutrients, hindering their growth, and making them susceptible to diseases. In acidic soils, elements like aluminum, iron, and manganese can become toxic to plants, while other nutrients like calcium, magnesium, and phosphorus can become limiting factors. A common practice to amend acidic soils is by adding lime (CaO), which is a basic compound that can neutralize the excess hydrogen ions (H⁺) responsible for soil acidity. When lime is added to the soil, it undergoes the following reaction to form calcium hydroxide (Ca(OH)₂), which neutralizes soil acidity: \[CaO (s) + H_2O (l) \rightarrow Ca(OH)_2 (aq)\] Then, calcium hydroxide reacts with the excess hydrogen ions that cause soil acidity: \[Ca(OH)_2 (aq) + 2H^+ (aq) \rightarrow Ca^{2+} (aq) + 2H_2O (l)\] By neutralizing the acidic soil, the gardener allows for better nutrient availability and improved plant growth and health.