Acid Rain - Meaning, Definition, Causes, Effects, Examples, FAQs

What is acid rain?

Acid rain definition: Acid rain refers to any precipitation that is more acidic than normal water, including rain, snow, fog, and dew. As carbon dioxide gas combines with it to generate weak carbonic acid, regular rain is mildly acidic, with a pH of around 5.6. For example:

CO₂ + H₂O → H₂CO₃

There are two types of acidic deposition: wet and dry. Dry deposition of harmful particles and gases adheres to the ground through dust and smoke in the absence of precipitation.

As natural and unpolluted rainwater has a pH between 5.6 and 6.5 (acidic) due to the reaction of water with CO₂, it is classified as acid rain when its pH is less than 5.6. The acidity of rainwater is caused by the natural presence of three compounds and acid rain contains (CO₂, NO_x, and SO₂) in the troposphere, which are emitted through coal combustion in power plants and gasoline combustion in automobiles. Acid rain pH can range from 5.6 to 3.5, and in certain situations, it can even fall below 2.

What Causes Acid Rain

Mineral acids such as carbonic acid, nitric acid, and sulphuric acid are the principal causes of acid rain.

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Acid rain causes

1. Carbonic acid is formed when carbon dioxide gas molecules react with water molecules (H₂CO₃). Carbonic acid's capability (H₂CO₃). The H₂CO₃ (carbonic acid) molecule possesses the potential to supply H⁺; because of this, the molecule is classified as an acid. As a result, it is in charge of reducing the pH of a solution.

CO₂ + H₂O → H₂CO₃

H₂CO₃ → H⁺ + HCO₃^-

2. The molecule of nitric oxide (NO), which is generated during lightning storms by the reaction of nitrogen and oxygen, two prevalent atmospheric gases, contributes to the natural decrease of pH (acidity) of precipitation. Nitric oxide (NO) is oxidized to nitrogen dioxide (NO₂) in the air, which then reacts with water to form nitric acid (HNO₃). In a reaction similar to the dissociation of carbonic acid indicated in the equation below, this acid dissociates in water to produce hydrogen ions (H⁺) and nitrate ions (NO₃^-), reducing the pH of the solution once more.

NO + ½ O₂ (g) → NO₂ (g)

N₂ (g) + O₂ (g) → 2NO (when lightning strikes in the atmosphere, a reaction occurs.)

3NO₂ (g) + H₂O → 2HNO₃ (aq) + NO (g)

Nitric acid is responsible for around one-fourth of the pH drop in rain (HNO₃).

The presence of sulphuric acid (H₂SO₄) in rainwater accounts for the reduction of pH in most water bodies. Despite the fact that sulphuric acid is produced naturally. Sulphuric acid is produced nearly completely by human activity, particularly the combustion of sulphur-containing fossil fuels in power plants. It is produced naturally in trace amounts through biological decomposition and volcanic activity.

Sulphur in these fossil fuels reacts with water to generate sulphuric acid when they are burned.

SO₂ (g) + O₂ → SO₃ (g) + H₂O → H₂SO₄

Sulphuric acid is an extremely powerful acid. As a result, it is regarded as a strong electrolyte that easily dissociates in water to produce H⁺ and HSO₄^- ions. The hydronium ion (H⁺) and sulphate ion may dissociate further from the HSO₄^- ion (SO₄^2-) As a result of the presence of H₂SO₄, the concentration of H⁺ ions in the rainwater rises substantially, and the pH decreases to a dangerous level.

H₂SO₄ → HSO₄^- + H⁺

HSO₄^- → SO₄^2-+ H⁺

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Environmental Effects of Acid Rain

Acid rain increases the number of inorganic and biological reactions that have negative environmental consequences, resulting in a global environmental disaster.

1. Many huge lakes have become so acidic (low pH lake) that fish can no longer survive in them.

2. The breakdown of many naturally occurring soil minerals produces metal ions. These metal ions are then swept away in the runoff, resulting in a variety of consequences:

a) The mobility of harmful ions such as Al³⁺ in the water supply increases due to the acidic situation.

b) The loss of essential minerals, such as Ca²⁺, from the soil in the process of neutralizing sulphuric acid, which generates a Ca²⁺ deficit, kills trees and damages crops.

3. It affects both animals and people' respiratory systems.

4. Acid rain has an impact on the aquatic ecosystem when it falls and runs into rivers and ponds. It creates water pollution by changing the chemical composition of the water to a state that is damaging to the aquatic ecosystem's ability to exist.

5. Corrosion of water pipes is also a result of acid rain. As a result, heavy metals such as iron, lead, and copper are leached into drinking water.

6. It causes damage to stone and metal structures and monuments.

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Examples of Acid rain

Acid rain has a significant impact on the Taj Mahal, one of the world's seven wonders. Many companies in the city of Agra produce sulphur and nitrogen oxides into the atmosphere. People continue to utilize low-quality coal and firewood as a source of household energy, exacerbating the problem. Acid rain reacts with marble (calcium carbonate) in the following way:

CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂

The corrosion of this lovely monument is caused by the production of calcium sulphate.

2. The Statue of Liberty, which is made of copper, has also been affected by the cumulative impact of acid rain and oxidation for over 30 years and is thus turning green.

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