This chapter focuses on water properties, water cycle, pollution, and treatment methods.
Created & Curated By S.K. Sinha
Enhanced Theory with Definitions, Examples & Concepts
Water: A colorless, odorless, and tasteless liquid compound with chemical formula H₂O. Essential for all life forms on Earth.
Universal Solvent: Water's ability to dissolve more substances than any other liquid, earning it the title "universal solvent."
Hydrosphere: The total amount of water on Earth including oceans, lakes, rivers, groundwater, ice caps, and water vapor.
💧 UNIQUE PROPERTIES OF WATER 💧
Physical and Chemical Characteristics:
ICE (0°C)LIQUID WATERSTEAM (100°C)
Water exists in all three states naturally on Earth!
Water Molecule Structure
H₂O Molecule: HOH
Bent shape with 104.5° bond angle
Physical Properties of Water
1. Physical State Properties
Characteristics:
• Colorless, odorless, tasteless
• Melting point: 0°C (273 K)
• Boiling point: 100°C (373 K)
• Density: 1 g/cm³ at 4°C
• Maximum density at 4°C
Anomalous Expansion: Water expands when it freezes, making ice less dense than liquid water.
2. Thermal Properties
Heat Capacity:
• High specific heat capacity
• High latent heat of fusion
• High latent heat of vaporization
• Excellent heat conductor
• Temperature regulator
Applications: Climate moderation, body temperature regulation, industrial cooling
3. Solvent Properties
Universal Solvent:
• Dissolves ionic compounds
• Dissolves polar molecules
• Forms hydrogen bonds
• High dielectric constant
• Excellent ionizing medium
Dissolves: Salt, sugar, acids, bases, many gases, nutrients
Water Phase Transitions: Ice ⇌ Water (0°C) ⇌ Steam (100°C) at 1 atm pressure
The Water Cycle
🌊 THE WATER CYCLE 🌊
Continuous circulation of water through Earth's systems
Powered by solar energy and gravity!
☀️ WATER CYCLE PROCESSES ☀️
Evaporation: Solar energy converts liquid water to water vapor from oceans, lakes, rivers
Transpiration: Plants release water vapor through their leaves
Condensation: Water vapor cools and forms tiny droplets in clouds
Precipitation: Water falls as rain, snow, sleet, or hail
Collection: Water gathers in water bodies and seeps into groundwater
Infiltration: Water soaks into soil and becomes groundwater
Importance of Water Cycle:
• Provides fresh water supply
• Maintains Earth's temperature balance
• Distributes nutrients globally
• Supports all ecosystems
• Enables weather patterns
• Cleanses the atmosphere
Sources of Water
Source Type
Examples
Characteristics
Uses
Surface Water
Rivers, lakes, streams, ponds
Easily accessible, may be polluted
Drinking, irrigation, industry
Groundwater
Wells, springs, aquifers
Filtered by soil, usually cleaner
Drinking water, agriculture
Rainwater
Direct precipitation
Pure but may be acidic in cities
Harvesting, irrigation
Seawater
Oceans, seas
High salt content, needs treatment
After desalination
Ice/Snow
Glaciers, polar ice caps
Frozen freshwater reserves
Seasonal water supply
Hard Water and Soft Water
Hard Water
Definition: Water containing dissolved salts of calcium and magnesium, primarily Ca²⁺ and Mg²⁺ ions.
Adding Washing Soda: Na₂CO₃ precipitates Ca²⁺ and Mg²⁺ ions
Ion Exchange: Resin exchanges Ca²⁺/Mg²⁺ with Na⁺ ions
Distillation: Complete removal of all dissolved salts
Water Pollution
⚠️ WATER POLLUTION CRISIS ⚠️
Contamination of water bodies by harmful substances
Threatens all life forms and ecosystems!
Pollution Source
Pollutants
Effects
Examples
Industrial Waste
Heavy metals, chemicals, toxins
Cancer, organ damage, death
Mercury, lead, pesticides
Sewage
Bacteria, viruses, organic matter
Diseases, oxygen depletion
E.coli, cholera, typhoid
Agricultural Runoff
Fertilizers, pesticides
Eutrophication, toxicity
Nitrates, phosphates
Oil Spills
Petroleum products
Marine life death, ecosystem damage
Crude oil, gasoline
Plastic Waste
Microplastics, chemicals
Food chain contamination
Bottles, bags, packaging
Health Effects of Polluted Water:
• Waterborne diseases (cholera, typhoid, dysentery)
• Heavy metal poisoning
• Cancer and genetic disorders
• Skin and eye irritation
• Digestive problems
• Neurological damage
Water Treatment
🏭 WATER TREATMENT PROCESSES 🏭
Making water safe for human consumption
Multiple stages of purification!
🔬 WATER TREATMENT STEPS 🔬
Screening: Removes large debris and floating materials
Coagulation: Alum added to bind small particles together
Flocculation: Gentle mixing forms larger clumps (flocs)
Sedimentation: Heavy particles settle at bottom
Filtration: Water passes through sand, gravel, carbon filters
Disinfection: Chlorine, UV, or ozone kills harmful microorganisms
pH Adjustment: Lime added to maintain proper pH levels
Boiling Time: 15-20 minutes for complete sterilization
Advanced Treatment
Modern Techniques:
• Reverse Osmosis (RO)
• Ion Exchange
• Activated Carbon
• Membrane Bioreactors
• Electrochemical treatment
RO Process: Removes 95-99% of dissolved salts and contaminants
Water Conservation
💚 WATER CONSERVATION METHODS 💚
Save water for future generations
Every drop counts in water conservation!
Household Conservation
Simple Steps:
• Fix leaky taps and pipes
• Use water-efficient appliances
• Take shorter showers
• Collect rainwater
• Reuse greywater for plants
• Use bucket instead of hose
Water Saving: A dripping tap wastes 15 liters per day
Community Conservation
Large Scale Methods:
• Rainwater harvesting
• Watershed management
• Drip irrigation
• Water recycling plants
• Public awareness campaigns
• Government policies
Irrigation Efficiency: Drip irrigation saves 30-50% water
Water Scarcity Facts:
• Only 2.5% of Earth's water is fresh water
• 1 billion people lack access to clean water
• Agriculture uses 70% of available freshwater
• By 2025, 1.8 billion people may face water scarcity
• 40% of global population affected by water stress
Uses of Water
Category
Specific Uses
% of Total Use
Importance
Domestic
Drinking, cooking, cleaning, bathing
8-10%
Essential for survival
Agricultural
Irrigation, livestock, crop processing
70%
Food security
Industrial
Manufacturing, cooling, cleaning
20%
Economic growth
Energy
Hydroelectric power, thermal cooling
5%
Power generation
Environmental
Ecosystem maintenance, wildlife
Variable
Biodiversity protection
Water Quality Parameters: pH (6.5-8.5) | TDS < 500 ppm | Chlorine < 5 ppm | Zero bacteria
Section B: Short Answer Questions
Q1. What is water? Write its chemical formula and molecular structure.
Answer: Water is a colorless, odorless, tasteless liquid compound. Chemical formula: H₂O. Structure: Bent molecule with 104.5° bond angle, consisting of 2 hydrogen atoms covalently bonded to 1 oxygen atom.
Q2. Why is water called the universal solvent?
Answer: Water dissolves more substances than any other liquid due to its polar nature, ability to form hydrogen bonds, and high dielectric constant. It can dissolve ionic compounds, polar molecules, acids, bases, and many gases.
Q3. Explain the water cycle with its main processes.
Answer: Water cycle is continuous circulation of water through evaporation (from water bodies), transpiration (from plants), condensation (cloud formation), precipitation (rain/snow), and collection (in water bodies and groundwater).
Q4. Differentiate between hard water and soft water.
Answer: Hard water contains dissolved Ca²⁺ and Mg²⁺ ions, forms scum with soap, causes scale in pipes. Soft water has low Ca²⁺/Mg²⁺ content, forms lather easily, doesn't cause scaling.
Answer: Screening, coagulation (alum addition), flocculation, sedimentation, filtration (sand, gravel, carbon), disinfection (chlorination), pH adjustment, and storage in clean reservoirs.
Q7. Why does ice float on water?
Answer: Ice floats because it's less dense than liquid water. When water freezes, molecules form a crystalline structure with more space between them, making ice about 8% less dense than water.
Q8. What are the methods to soften hard water?
Answer: Boiling (removes temporary hardness), adding washing soda (Na₂CO₃), ion exchange resins, distillation, and using lime-soda process for large-scale treatment.
Q9. List five water conservation methods.
Answer: Fix leaks, rainwater harvesting, drip irrigation, water recycling, shorter showers, using water-efficient appliances, and greywater reuse for gardening.
Q10. What are the main uses of water in daily life?
Answer: Drinking, cooking, cleaning, bathing, agriculture (irrigation), industry (manufacturing, cooling), power generation (hydroelectric), transportation, and recreational activities.
Section C: Long Answer Questions
Q1. Describe the unique properties of water and explain their importance in sustaining life.
Solution: Water has several unique properties: High specific heat capacity helps regulate temperature in organisms and climate. Universal solvent property enables transport of nutrients and waste in living systems. Anomalous expansion makes ice less dense, protecting aquatic life in winter. High surface tension enables capillary action in plants. Chemical stability ensures it doesn't break down easily. These properties make water essential for biochemical reactions, temperature regulation, transport systems, and maintaining Earth's climate, making life possible.
Q2. Explain the water cycle in detail and discuss its environmental importance.
Solution: The water cycle is powered by solar energy and gravity. Evaporation from oceans, lakes converts water to vapor. Transpiration from plants adds moisture. Rising vapor cools and condenses into clouds. Precipitation brings water back as rain/snow. Surface runoff feeds rivers, while infiltration replenishes groundwater. Environmental importance: distributes fresh water globally, maintains ecosystem balance, regulates climate, cleanses atmosphere, supports biodiversity, enables agriculture, and provides renewable water supply. Disruption through deforestation or pollution affects global water availability and climate patterns.
Q3. Discuss water pollution, its sources, effects, and prevention measures.
Solution: Water pollution occurs when harmful substances contaminate water bodies. Sources include industrial discharge (heavy metals, chemicals), sewage (pathogens, organic matter), agricultural runoff (fertilizers, pesticides), oil spills, plastic waste, and urban stormwater. Effects: waterborne diseases, ecosystem disruption, eutrophication, bioaccumulation in food chains, economic losses. Prevention: proper waste treatment, industrial regulation, sustainable agriculture, plastic reduction, sewage treatment plants, public awareness. Individual actions: proper disposal, reduced chemical use, water conservation, supporting clean initiatives.
Q4. Explain water treatment processes and the importance of clean water supply.
Solution: Water treatment involves multiple stages: Screening removes large debris. Coagulation with alum binds particles. Flocculation forms settleable clumps. Sedimentation separates heavy particles. Filtration through sand, gravel, activated carbon removes remaining impurities. Disinfection with chlorine/UV kills microorganisms. pH adjustment ensures water quality. Importance: prevents waterborne diseases, ensures public health, supports economic development, maintains quality of life. Advanced methods like RO, ion exchange provide ultra-pure water. Regular monitoring ensures safety standards are met.
Q5. Compare hard water and soft water, explaining methods to convert hard water to soft water.
Solution: Hard water contains dissolved Ca²⁺ and Mg²⁺ ions from limestone, gypsum. It forms scum with soap, causes scale buildup, wastes soap, affects appliance efficiency. Soft water has minimal dissolved salts, forms good lather, prevents scaling. Conversion methods: Temporary hardness removed by boiling (bicarbonates decompose). Permanent hardness treated with washing soda (precipitates salts), ion exchange (resin swaps ions), distillation (complete removal). Lime-soda process for large scale. Choice depends on hardness type and scale of treatment required.
Q6. Discuss water conservation methods and their necessity for sustainable development.
Solution: Water conservation is critical due to increasing demand and limited supply. Household methods: fix leaks, efficient appliances, shorter showers, rainwater harvesting, greywater reuse. Agricultural: drip irrigation, drought-resistant crops, precision farming. Industrial: recycling, closed-loop systems, efficient processes. Community: watershed management, water recycling plants, public awareness. Necessity: growing population, climate change, pollution, uneven distribution. Only 2.5% Earth's water is fresh, 1 billion lack access. Conservation ensures sustainable supply, reduces environmental impact, supports economic development, and protects ecosystems for future generations.
Q7. Explain the different sources of water and their suitability for various uses.
Solution: Water sources include surface water (rivers, lakes) - easily accessible but may be polluted, suitable for irrigation after treatment. Groundwater (wells, aquifers) - naturally filtered, usually cleaner, good for drinking. Rainwater - pure but may be acidic, excellent for harvesting. Seawater - abundant but requires desalination, expensive. Ice/snow - seasonal freshwater storage. Recycled water - treated wastewater, suitable for irrigation, industry. Choice depends on availability, quality, cost, and intended use. Quality testing essential for drinking water. Multiple sources ensure supply security during droughts or contamination events.
Q8. Describe the role of water in human body and explain why adequate hydration is essential.
Solution: Water comprises 60-70% of human body weight. Functions: solvent for nutrients, waste transport via blood/urine, temperature regulation through sweating, joint lubrication, digestive processes, cellular metabolism, maintains blood pressure and volume. Dehydration causes fatigue, headaches, reduced cognitive function, kidney problems, heat stroke. Daily requirement: 2-3 liters depending on activity, climate, health. Quality matters - contaminated water causes diseases like cholera, typhoid, dysentery. Clean water access is fundamental human right, essential for health, productivity, dignity. Adequate hydration improves physical performance, mental clarity, and overall wellbeing.