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Chemistry - Atmospheric Pollution (Acid Rain, Greenhouse Effect, Ozone Depletion)

Grade 9ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Atmospheric Pollution: The presence of harmful substances in the air that cause adverse effects on living organisms and the environment, primarily caused by SO2SO_2, NOxNO_x, and particulate matter.

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Acid Rain: Precipitation with a pHpH less than 5.65.6. It is formed when oxides of sulfur (SO2SO_2) and nitrogen (NOxNO_x) react with atmospheric moisture to form H2SO4H_2SO_4 and HNO3HNO_3.

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Greenhouse Effect: The process by which greenhouse gases like CO2CO_2, CH4CH_4, N2ON_2O, and CFCsCFCs trap heat (infrared radiation) in the Earth's atmosphere, maintaining the planet's warmth.

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Global Warming: The steady increase in the Earth's average surface temperature due to the enhanced Greenhouse Effect caused by increased levels of CO2CO_2 and other pollutants.

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Ozone Layer (O3O_3): A protective layer in the stratosphere that absorbs harmful Ultraviolet (UVUV) radiation from the sun.

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Ozone Depletion: The thinning of the O3O_3 layer caused by Chlorofluorocarbons (CFCsCFCs), which release chlorine radicals (Cl∙Cl^{\bullet}) that catalyze the breakdown of O3O_3 into O2O_2.

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Stone Leprosy: The erosion and yellowing of marble monuments (like the Taj Mahal) due to the reaction between CaCO3CaCO_3 and acid rain.

📐Formulae

S+O2→SO2S + O_2 \rightarrow SO_2

2SO2+O2+2H2O→2H2SO4 (Sulfuric Acid in Acid Rain)2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4 \text{ (Sulfuric Acid in Acid Rain)}

4NO2+2H2O+O2→4HNO3 (Nitric Acid in Acid Rain)4NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3 \text{ (Nitric Acid in Acid Rain)}

CaCO3+H2SO4→CaSO4+H2O+CO2 (Effect on Marble)CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2 \text{ (Effect on Marble)}

O2→UVO+O followed by O+O2→O3O_2 \xrightarrow{UV} O + O \text{ followed by } O + O_2 \rightarrow O_3

CFCl3→UVCFCl2+Cl∙ (CFC dissociation)CFCl_3 \xrightarrow{UV} CFCl_2 + Cl^{\bullet} \text{ (CFC dissociation)}

Cl∙+O3→ClO∙+O2 (Ozone destruction)Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2 \text{ (Ozone destruction)}

💡Examples

Problem 1:

Explain the chemical reaction behind the yellowing of the Taj Mahal due to acid rain.

Solution:

CaCO3+H2SO4→CaSO4+H2O+CO2CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2

Explanation:

The sulfuric acid (H2SO4H_2SO_4) present in acid rain reacts with the calcium carbonate (CaCO3CaCO_3) of the marble. This converts the marble into calcium sulfate (CaSO4CaSO_4), which is a powdery substance that gets washed away, causing 'Stone Leprosy' and discoloration.

Problem 2:

Identify the primary Greenhouse gases and their sources.

Solution:

CO2CO_2 (Burning fossil fuels), CH4CH_4 (Paddy fields, livestock), N2ON_2O (Fertilizers), and CFCsCFCs (Refrigerants).

Explanation:

These gases possess the ability to absorb long-wave infrared radiation reflected from the Earth's surface, preventing it from escaping into space.

Problem 3:

How do CFCsCFCs contribute to the depletion of the ozone layer?

Solution:

CFCl3→UVCFCl2+Cl∙CFCl_3 \xrightarrow{UV} CFCl_2 + Cl^{\bullet} and Cl∙+O3→ClO+O2Cl^{\bullet} + O_3 \rightarrow ClO + O_2.

Explanation:

In the stratosphere, UVUV radiation breaks down CFCsCFCs to release highly reactive free chlorine radicals (Cl∙Cl^{\bullet}). A single chlorine radical can destroy thousands of ozone molecules in a chain reaction.