10th Class Chemistry Chapter 15 Notes | Get Now

10th Class Chemistry Chapter 15 Notes are exactly what you need if you’re preparing for your board exams and want a clear, easy-to-follow summary of “Environmental Chemistry II: Water.” This chapter is one of the most scoring units in the 10th class chemistry syllabus because it deals with everyday concepts like water properties, hardness, and pollution — topics you can relate to real life. Below, we’ve broken down every important concept from the chapter so you can revise quickly and confidently.

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Physical Properties of Water

Understanding water’s basic nature is the foundation of this chapter. These 10th Class Chemistry Chapter 15 Notes highlight the key physical properties every student must remember:

• Water is neutral to litmus.
• Its freezing point is 0°C and boiling point is 100°C at sea level.
• Maximum density of water is 1 g/cm³ at 4°C.
• It acts as an excellent solvent for both ionic and molecular compounds.
• Water has an unusually high heat capacity (about 4.2 J/g·K), roughly six times greater than rocks — this property keeps Earth’s temperature balanced.
• High surface tension allows capillary action, helping water rise from plant roots to leaves.

Why Is Water Called a Universal Solvent?

Water dissolves almost every mineral due to two unique properties:

1. Polarity of the water molecule – one end is partially positive, the other partially negative.
2. Exceptional hydrogen bonding ability – allows water to interact with polar and ionic substances easily.

This polar nature explains why salts like NaCl and KCl dissolve in water, while non-polar substances like benzene and octane do not.

Hydrogen Bonding in Water Molecules

Each water molecule can form hydrogen bonds with four other water molecules, arranged in a tetrahedral shape. This special bonding lets water dissolve organic compounds containing hydroxyl (-OH) groups, such as alcohols, sugars, and organic acids.

Occurrence and Distribution of Water

Since this topic often appears in short questions, our 10th Class Chemistry Chapter 15 Notes summarize the water distribution clearly:

• Oceans: 97%
• Glaciers and ice caps: 2.1%
• Ground water: 0.6%
• Inland water (rivers, lakes, streams): 0.2%
• Atmospheric water: 0.001%

Only a small fraction of Earth’s water is actually potable, which is why sea water is unfit for drinking due to its high salt content.

Hard Water and Soft Water

This is one of the most important sections in these 10th Class Chemistry Chapter 15 Notes, as numerical and conceptual questions are frequently asked from here.

What Causes Hardness in Water?

Rainwater absorbs carbon dioxide from the atmosphere. As it passes through soil, it converts insoluble carbonates of calcium and magnesium into soluble bicarbonates, making water “hard.”

Types of Hardness

• Temporary Hardness – caused by bicarbonates of calcium and magnesium.
• Permanent Hardness – caused by sulphates and chlorides of calcium and magnesium.

Disadvantages of Hard Water

• Consumes more soap during washing.
• Can cause stomach disorders if consumed regularly.
• Unsuitable for boilers, turbines, and steam engines due to scale formation.

Removing Temporary Hardness

1. Boiling Method – Calcium bicarbonate decomposes on boiling to form insoluble calcium carbonate.
2. Clark’s Method – Adding slaked lime [Ca(OH)₂] precipitates calcium and magnesium ions.

Removing Permanent Hardness

• Washing Soda (Na₂CO₃) – converts calcium and magnesium salts into insoluble carbonates.
• Sodium Zeolite Method – an ion-exchange resin that swaps sodium ions for calcium and magnesium ions in hard water. The resin can later be regenerated using concentrated NaCl solution.

Water Pollution and Its Causes

Water pollution is a major topic in these 10th Class Chemistry Chapter 15 Notes, covering multiple sources of contamination.

Industrial Waste

Factories discharge chemicals, heavy metals, and toxic effluents into water bodies, which:

• Lower the water quality.
• Reduce dissolved oxygen, harming aquatic life.
• Contaminate groundwater and cause diseases like cancer and gastro issues.

Heavy metals such as cadmium, lead, and mercury are especially dangerous — causing kidney damage, high blood pressure, and neurological problems.

Household Waste and Detergents

Detergents are non-biodegradable and remain in water for long periods. Their phosphate content triggers rapid algae growth, which depletes oxygen when the algae decay, harming aquatic life.

Agricultural Effluents

Fertilizers and pesticides used in farming introduce nitrate and phosphate salts into nearby water sources. This causes excessive algae growth, oxygen depletion, and eventually the death of aquatic organisms.

Effects of Water Pollution

• Increases risk of diseases like cholera, typhoid, and diarrhea.
• Harms animals, birds, and aquatic ecosystems.
• Disrupts food chains.
• Reduces the aesthetic and practical value of lakes and rivers.

Water-Borne Diseases

A key exam-focused section in these 10th Class Chemistry Chapter 15 Notes explains the major diseases spread through contaminated water:

• Diarrhea – caused by viruses, bacteria, or parasites.
• Dysentery – bacterial or parasitic infection causing bloody stools.
• Cholera – caused by Vibrio cholerae bacteria; leads to severe diarrhea.
• Cryptosporidiosis – caused by a protozoan parasite found in lakes and rivers.
• Hepatitis – liver inflammation; Hepatitis A and E spread through contaminated water.
• Typhoid – bacterial disease spread by polluted water or food.
• Hookworm infection – parasitic worms entering through skin, causing anemia.

Preventing Water-Borne Diseases

1. Ensure safe and properly treated drinking water.
2. Dispose of sewage through proper sanitation systems.
3. Control the use of toxic chemicals and pesticides.

Chemistry of Swimming Pool Cleanliness

Swimming pools are disinfected using chlorination. Chlorine reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid. HOCl further ionizes into hypochlorite ions, and both HOCl and OCl⁻ effectively kill bacteria and micro-organisms.

FAQs

Q1. What is covered in 10th Class Chemistry Chapter 15 Notes?
These notes cover water’s physical properties, hardness types, water pollution causes, water-borne diseases, and swimming pool chlorination — everything needed for board exam preparation.

Q2. Why is water called a universal solvent?
Water is called a universal solvent because of its polarity and strong hydrogen bonding ability, allowing it to dissolve most ionic and polar molecular compounds easily.

Q3. What causes hardness in water?
Hardness occurs when rainwater absorbs carbon dioxide and dissolves calcium and magnesium salts from soil, forming bicarbonates, sulphates, and chlorides that make water “hard.”

Q4. How can temporary hardness be removed?
Temporary hardness can be removed by boiling water or by adding slaked lime through Clark’s method, which precipitates calcium and magnesium ions out of the solution.

Q5. What are common water-borne diseases?
Common water-borne diseases include cholera, typhoid, dysentery, hepatitis A and E, and hookworm infections — all spread through contaminated drinking water.

Q6. How is water pollution caused by detergents?
Detergents are non-biodegradable and contain phosphates that promote rapid algae growth. When algae decay, they consume dissolved oxygen, harming aquatic life in the process.