Environmental chemistry questions 1-7

ENVIRONMENTAL CHEMISTRY – EXAM-ORIENTED NOTES

Section–A: 5 Marks Questions

1. Write the importance of environment

Introduction

The environment includes all living and non-living components surrounding organisms, such as air, water, soil, plants, animals and microorganisms. A clean and balanced environment is essential for the survival and development of living organisms.

Importance of Environment

Provides basic necessities: It supplies air, water, food and shelter required for life.

Maintains ecological balance: Interaction between living organisms and their surroundings maintains ecosystem stability.

Supports biodiversity: Forests, oceans, wetlands and other ecosystems provide habitats for diverse organisms.

Provides natural resources: Environment supplies minerals, fossil fuels, forests, water and other resources.

Regulates climate: Forests, oceans and atmosphere help regulate temperature, rainfall and climate.

Supports agriculture: Soil, water, sunlight and nutrients are essential for crop production.

Provides economic resources: Many industries depend on natural resources such as minerals, timber and water.

Recycles materials: Natural cycles such as the carbon, nitrogen and water cycles recycle essential elements.

Supports human health: Clean air, safe drinking water and unpolluted surroundings are essential for good health.

Provides aesthetic and recreational value: Natural landscapes provide opportunities for recreation and improve quality of life.

Conclusion

Therefore, conservation and sustainable utilization of environmental resources are essential for the survival of present and future generations.

2. Write a note on Hydrological Cycle

Definition

The hydrological cycle or water cycle is the continuous circulation of water between the atmosphere, land and oceans.

Main Steps

1. Evaporation:

Solar energy converts water from oceans, rivers, lakes and soil into water vapour.

2. Transpiration:

Plants release water vapour into the atmosphere through their leaves. The combined process is called evapotranspiration.

3. Condensation:

Water vapour rises, cools and changes into tiny water droplets, forming clouds.

4. Precipitation:

Water falls from clouds to the Earth's surface as rain, snow, sleet or hail.

5. Infiltration:

Some water enters the soil and replenishes groundwater.

6. Surface runoff:

Water flows over the land into streams, rivers, lakes and eventually oceans.

7. Groundwater flow:

Groundwater moves through soil and rocks and ultimately returns to rivers, lakes or oceans.

Simple Flow Diagram

Oceans/Lakes → Evaporation → Water vapour → Condensation → Clouds → Precipitation → Surface runoff + Infiltration → Rivers/Groundwater → Oceans

Importance

Maintains the availability of freshwater.

Recharges groundwater.

Supports agriculture and ecosystems.

Regulates climate and temperature.

Provides water for domestic and industrial purposes.

3. What are the sources of air pollution?

Definition

Air pollution is the presence of harmful solid, liquid or gaseous substances in the atmosphere at concentrations that adversely affect living organisms and the environment.

Major Sources

A. Natural Sources

Volcanic eruptions – release SO₂, ash and other gases.

Forest fires – release smoke, CO, CO₂ and particulate matter.

Dust storms – increase suspended particulate matter.

Decomposition of organic matter – releases gases such as methane and ammonia.

Pollen and spores – contribute to biological air pollutants.

B. Anthropogenic Sources

Automobiles: Produce CO, NOₓ, hydrocarbons and particulate matter.

Industries: Release SO₂, NOₓ, particulate matter and various toxic gases.

Thermal power plants: Burning coal releases SO₂, NOₓ, CO₂ and fly ash.

Domestic fuel combustion: Burning coal, wood and biomass produces smoke and harmful gases.

Agricultural activities: Fertilizers and pesticides contribute to ammonia and other pollutants.

Construction activities: Generate dust and particulate matter.

Waste burning: Releases smoke, toxic gases and fine particles.

Conclusion

Control of emissions from industries, automobiles and domestic combustion is essential for maintaining clean air.

4. Explain Photochemical Smog

Definition

Photochemical smog is a brownish atmospheric haze formed by the reaction of nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in the presence of sunlight.

It is commonly called oxidizing smog or Los Angeles-type smog.

Formation

Automobile exhaust releases:

NOₓ + Hydrocarbons + Sunlight → Photochemical reactions → O₃ + PAN + Aldehydes

First, nitrogen dioxide absorbs sunlight:

NO₂ + hν → NO + O

The oxygen atom reacts with molecular oxygen:

O + O₂ → O₃

Thus, ozone (O₃) is produced.

In the presence of hydrocarbons/VOCs, further reactions produce peroxyacetyl nitrate (PAN) and aldehydes.

Major Components

Ozone (O₃)

PAN (Peroxyacetyl nitrate)

Nitrogen oxides

Aldehydes

Other oxidants

Effects

Causes eye irritation.

Produces respiratory problems.

Damages plant leaves and reduces crop yield.

Causes reduced visibility.

Damages rubber, paints and other materials.

Ozone can cause oxidative damage to living organisms.

Control

Reduce automobile emissions.

Use public transport and electric vehicles.

Control VOC emissions.

Use catalytic converters.

Promote clean fuels and renewable energy.

5. Define BOD and COD

BOD – Biochemical Oxygen Demand

Definition

BOD is the amount of dissolved oxygen required by microorganisms to biologically decompose biodegradable organic matter present in a water sample under specified conditions.

It is generally expressed in:

mg O₂/L

A standard BOD test is commonly conducted for 5 days at 20°C, known as BOD₅.

Significance

Indicates the amount of biodegradable organic pollution.

Higher BOD → Greater organic pollution.

High BOD can reduce dissolved oxygen in water and harm aquatic organisms.

COD – Chemical Oxygen Demand

Definition

COD is the amount of oxygen required to chemically oxidize organic and other oxidizable substances present in a water sample.

It is expressed as:

mg O₂/L

Significance

Measures the total chemically oxidizable pollution.

COD is generally greater than BOD because it includes substances that may not be readily biodegradable.

Higher COD indicates greater pollution.

Difference between BOD and COD

BOD COD

Biological oxidation Chemical oxidation

Uses microorganisms Uses chemical oxidizing agents

Measures biodegradable organic matter Measures chemically oxidizable matter

Takes several days Can be determined relatively quickly

Generally lower Generally higher

6. Write a note on Eutrophication

Definition

Eutrophication is the enrichment of a water body with nutrients, particularly nitrogen and phosphorus, resulting in excessive growth of algae and aquatic plants.

Causes

Agricultural fertilizers

Domestic sewage

Industrial wastewater

Detergents containing phosphates

Animal wastes

Surface runoff

Process

Nutrients → Excessive algal growth → Algal bloom → Death of algae → Microbial decomposition → Increased BOD → Depletion of dissolved O₂ → Death of aquatic organisms

Effects

Excessive algal growth or algal blooms.

Reduction in sunlight penetration.

Increased decomposition of dead organic matter.

Increase in BOD.

Depletion of dissolved oxygen.

Death of fish and other aquatic organisms.

Formation of unpleasant odours.

Loss of aquatic biodiversity.

Some algal blooms may produce harmful toxins.

Control Measures

Reduce phosphate-containing detergents.

Treat domestic sewage before discharge.

Control fertilizer use.

Prevent agricultural runoff.

Remove excess nutrients from wastewater.

Protect wetlands and buffer zones.

Conclusion

Proper management of nitrogen and phosphorus inputs is essential to prevent eutrophication.

7. Write about the toxicity of Lead

Introduction

Lead (Pb) is a toxic heavy metal that can enter the environment through industrial emissions, mining, batteries, paints, contaminated soil and water.

Sources of Lead Pollution

Lead-acid batteries

Mining and smelting industries

Lead-based paints

Industrial processes

Contaminated soil and dust

Some plumbing materials

Improper disposal of lead-containing wastes

Toxic Effects

1. Nervous system:

Lead can damage the nervous system and may cause learning and behavioural problems, particularly in children.

2. Blood:

It interferes with haemoglobin synthesis and can contribute to anaemia.

3. Kidneys:

Long-term exposure can damage kidney function.

4. Cardiovascular system:

Chronic exposure is associated with adverse cardiovascular effects.

5. Children:

Children are especially vulnerable because exposure can affect brain development and cognitive function.

6. Reproductive effects:

High or prolonged exposure may adversely affect reproductive health.

Prevention and Control

Eliminate lead-based paints and products where possible.

Proper disposal and recycling of lead-containing wastes.

Control industrial emissions.

Prevent contamination of drinking water.

Monitor lead levels in contaminated areas.

Use appropriate protective equipment in occupational settings.