(a) Write a chemical equation that describes the attack of acid rain on limestone, CaCO_. (b) If a limestone sculpture were treated to form a surface layer of calcium sulfate, would this help to slow down the effects of acid rain? Explain.

Acid rain contains, among other substances, acidic gases like sulfur dioxide (SO2) and nitrogen oxides (NOx). When these gases dissolve in water, they generate sulfuric acid (H2SO4) and nitric acid (HNO3), respectively. Limestone is mostly composed of calcium carbonate (CaCO3). When limestone is exposed to acid rain, it reacts with the acids to form calcium sulfate (CaSO4), calcium nitrate (Ca(NO3)2), carbon dioxide (CO2), and water (H2O). We can represent this reaction with the following balanced chemical equation: CaCO3 (s) + H2SO4 (aq) -> CaSO4 (s) + CO2 (g) + H2O (l) Here (s), (aq), (g), and (l) indicate the physical states of the reactants and products: solid, aqueous, gas, and liquid, respectively.

Suppose a limestone sculpture is treated with calcium sulfate (CaSO4) to form a surface layer on the sculpture. The goal is to find out if this treatment would protect the sculpture from the attacks of acid rain. When acid rain attacks limestone directly, the CaCO3 present in the limestone reacts with sulfuric acid (H2SO4) and nitric acid (HNO3) as seen in the previous step's chemical equation. This reaction leads to the dissolution and gradual erosion of the limestone over time. Now, let's consider the case where the limestone has been treated with and covered by a layer of calcium sulfate. The reactions that would likely occur involve the calcium sulfate with the sulfuric acid and nitric acid present in the acid rain: CaSO4 (s) + 2H2SO4 (aq) -> Ca(HSO4)2 (aq) + 2H2O (l) CaSO4 (s) + 2HNO3 (aq) -> Ca(NO3)2 (aq) + H2SO4 (aq) The first reaction, with sulfuric acid, is likely to be much slower than the direct reaction of acid rain on limestone. This is because the calcium sulfate formed is less soluble and less reactive than calcium carbonate. The second reaction, with nitric acid, generates calcium nitrate and an aqueous solution of sulfuric acid. In this case, the sulfuric acid formed can further react with the underlying limestone to continue the erosion process. Overall, treating a limestone sculpture with a surface layer of calcium sulfate would help to slow down the effects of acid rain to some extent. However, it may not provide complete protection, as trace amounts of acidic solutions could still penetrate the calcium sulfate layer and continue attacking the limestone. In addition, the weight and nature of the calcium sulfate layer might also affect the sculpture's appearance and integrity over time.