Question

(a) Write a chemical equation that describes the attack of acid rain on limestone, \(\mathrm{CaCO}_{3}\). (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.

Short answer

(a) The chemical equation for the reaction of acid rain (sulfuric acid) with limestone (CaCO3) is: \[CaCO_{3}(s) + H_{2}SO_{4}(aq) \rightarrow CaSO_{4}(s) + CO_{2}(g) + H_{2}O(l)\] (b) Yes, treating a limestone sculpture with a surface layer of calcium sulfate would help slow down the effects of acid rain, as calcium sulfate is more resistant to acid rain attack and creates a protective barrier preventing direct contact of acid with the limestone.

Step-by-step solution

(a) Identify the components of acid rain

Acid rain is caused mainly due to the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) from industries and automobiles. In the atmosphere, these gases react with water vapor to form sulfuric acid (H2SO4) and nitric acid (HNO3), which fall back to the earth's surface as acid rain.

(a) Write the chemical equation for acid rain reaction with limestone

Here, we will focus on the reaction of sulfuric acid (H2SO4) with limestone (CaCO3). When sulfuric acid comes into contact with limestone, it reacts to form calcium sulfate, carbon dioxide, and water. The balanced chemical equation for this reaction is: \[CaCO_{3}(s) + H_{2}SO_{4}(aq) \rightarrow CaSO_{4}(s) + CO_{2}(g) + H_{2}O(l)\]

(b) Determine if a calcium sulfate layer would help protect limestone sculptures

Now we need to examine if treating limestone sculptures with a surface layer of calcium sulfate would help slow down the effects of acid rain. Calcium sulfate is more resistant to acid rain attack as compared to calcium carbonate. Treating the surface of limestone sculptures with calcium sulfate will create a barrier between the limestone and the acid rain, preventing the direct contact of acid with the limestone CaCO3. Since calcium sulfate is relatively insoluble in water and doesn't react with acid rain like limestone, it will help slow down the decay of the limestone sculpture caused by acid rain. So, the answer to part (b) is yes, treating the limestone sculpture to form a surface layer of calcium sulfate would help slow down the effects of acid rain.

Key concepts

Chemical Reaction

Understanding chemical reactions is fundamental when exploring how acid rain affects limestone. A chemical reaction occurs when substances combine to form new compounds. In the case of acid rain, sulfuric acid (\(\text{H}_2\text{SO}_4\)) reacts with limestone (\(\text{CaCO}_3\)). This reaction results in the transformation of these reactants into new products, such as calcium sulfate, carbon dioxide, and water.

The specific chemical equation is: \[\text{CaCO}_{3}(s) + \text{H}_{2}\text{SO}_{4}(aq) \rightarrow \text{CaSO}_{4}(s) + \text{CO}_{2}(g) + \text{H}_{2}\text{O}(l)\]
When the acid rain comes in contact with limestone, the limestone slowly dissolves due to this chemical reaction. It's important to note that these reactions are part of what makes acid rain particularly damaging to buildings and sculptures made from limestone.

Calcium Sulfate

Calcium sulfate (\(\text{CaSO}_{4}\)) plays a crucial role in the context of limestone protection against acid rain. It is the main product when sulfuric acid reacts with limestone. One of the reasons calcium sulfate is beneficial is its relative insolubility in water, which makes it less prone to washing away.

Applying a layer of calcium sulfate can help protect limestone structures for several reasons:

• **Barrier Formation**: A calcium sulfate layer acts as a barrier between the limestone and corrosive acids, preventing direct contact of the acids with the limestone.
• **Durability**: Since calcium sulfate is less reactive with acids compared to calcium carbonate, it stays intact longer when exposed to acid rain.

In summary, using calcium sulfate as a protective layer on limestone can help in slowing down the degradation process caused by acid rain, preserving the longevity of limestone sculptures and structures.

Sulfur Dioxide

Sulfur dioxide (\(\text{SO}_2\)) is a significant contributor to acid rain. It is mainly produced by burning fossil fuels in industries and vehicles. When it is released into the atmosphere, sulfur dioxide reacts with water vapor to form sulfuric acid (\(\text{H}_2\text{SO}_4\)).

Here’s a quick overview of sulfur dioxide's role:

• **Acid Formation**: Upon reaction with atmospheric water, it transforms into sulfuric acid, a key component of acid rain.
• **Effect on Structures**: The sulfuric acid formed then causes damage to buildings and natural structures, especially those made with limestone.

Managing sulfur dioxide emissions is crucial in controlling acid rain. Strategies include using cleaner fuels, installing scrubbers in smokestacks, and developing alternative energy sources. Reducing sulfur dioxide emissions can significantly mitigate the harmful effects of acid rain on the environment and infrastructure.