Question

The acid not present in acid rain is (A) Peroxyacetylnitrate (B) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (C) \(\mathrm{HNO}_{3}\) (D) \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Short answer

The acid not present in acid rain is Carbonic acid (\(\mathrm{H}_{2} \mathrm{CO}_{3}\)). Hence, the correct answer is option (B) \(\mathrm{H}_{2} \mathrm{CO}_{3}\).

Step-by-step solution

Analyze the given options

Let's inspect each option in detail: (A) Peroxyacetylnitrate (PAN) - It is formed due to the reaction of nitrogen oxides and volatile organic compounds in the atmosphere. It is a component of smog and can be indirectly related to the formation of acid rain, but it is not directly present in acid rain. (B) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (Carbonic acid) - This acid is formed when carbon dioxide (\(\mathrm{CO}_{2}\)) dissolves in water. Carbon dioxide is a greenhouse gas, but it does not contribute to the formation of acid rain. (C) \(\mathrm{HNO}_{3}\) (Nitric acid) - Nitric acid is formed when nitrogen oxides (\(\mathrm{NO}_{x}\)) react with water in the atmosphere. It is a common component of acid rain. (D) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (Sulfuric acid) - Sulfuric acid is formed when sulfur dioxide (\(\mathrm{SO}_{2}\)) reacts with water in the atmosphere. It is another primary component of acid rain.

Identify the acid not present in acid rain

Based on the analysis above, we can conclude that Carbonic acid (\(\mathrm{H}_{2} \mathrm{CO}_{3}\)) is the acid not present in acid rain. Therefore, the correct answer is option (B) \(\mathrm{H}_{2} \mathrm{CO}_{3}\).

Key concepts

Peroxyacetylnitrate

Peroxyacetylnitrate, commonly known as PAN, might not be a household name, but it plays a significant role in our atmospheric chemistry. This compound, with the formula CH3COOONO2, is a powerful oxidant and is most familiar to scientists as a component of photochemical smog rather than acid rain.

What makes PAN particularly interesting is its formation—it's produced when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Due to its role in smog formation, it may indirectly contribute to the conditions that lead to acid rain, as it participates in the complex web of reactions in the atmosphere. However, it is not directly found in the composition of acid rain, differentiating it from some of its chemical cousins like nitric and sulfuric acids.

Carbonic Acid

Carbonic acid (H2CO3) is another player in the complex interplay of the Earth's atmosphere. It is a weak acid that forms when carbon dioxide (CO2) dissolves in water—think of a can of soda and how it turns fizzy when opened. In the context of acid rain though, carbonic acid plays a much more subdued role. It's such a mild acid that its effects on the environment are minimal when compared with the more robust acids like sulfuric and nitric acids.

It's worth noting that while CO2 levels impact climate change as a greenhouse gas, their contribution to acid rain is not significant enough to attribute them as a cause. Hence, carbonic acid, while present in rainwater due to natural CO2 dissolution, is not the environmental threat typically associated with the term 'acid rain'.

Nitric Acid

Nitric acid (HNO3) has a more notorious reputation in discussions about acid rain. This compound forms when nitrogen oxides from sources such as automobile exhausts or industrial emissions react with water vapor in the atmosphere. It is indeed one of the primary acids found in acid rain.

Its formation and deposition can lead to a variety of environmental issues, including the acidification of lakes and streams, damage to trees at high elevations, and the acceleration of decay of buildings and cultural monuments. Understanding the generation of nitric acid helps us comprehend the damage that anthropogenic activities can cause to our environment.

Sulfuric Acid

Sulfuric acid (H2SO4), by far, is one of the main culprits behind the phenomenon of acid rain. Its origin points to industrial processes, such as the burning of fossil fuels that contain sulfur compounds. Upon emission into the atmosphere, sulfur dioxide (SO2) reacts with water and oxygen, ultimately transforming into sulfuric acid.

Compared to carbonic acid, sulfuric acid is much stronger and has a significantly greater impact on ecosystems. It can disrupt aquatic life, leach nutrients from soils, and trigger vegetation decline. Because of its pivotal role in acid rain, controlling sulfur emissions is a crucial part of environmental protection policies to reduce the incidence and severity of acid rain.