Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Water and its importance → Water Purification ↓


Chlorination in water purification


Water is a vital resource for all living organisms. It is essential for drinking, cooking, cleaning, agriculture and many industrial processes. Therefore, it is of utmost importance to ensure that the water we use is clean and safe. One of the most common methods used to purify water is chlorination.

Chlorination is the process of adding chlorine or chlorine compounds to water. It is widely used to kill microorganisms, known as pathogens, that cause diseases. The chemical formula of chlorine is Cl 2 This method is used because it is effective, inexpensive and has a long-term effect in preventing waterborne diseases.

Why is water purification important?

Water purification is very important because untreated water may contain harmful microorganisms such as bacteria, viruses and parasites. These organisms can cause diseases such as cholera, dysentery and hepatitis. Therefore, it is important to clean drinking water to protect public health.

Apart from microorganisms, untreated water may also contain harmful chemicals, dirt, and debris. Drinking such water can be harmful to health. Therefore, purification helps in providing safe water for people to drink.

The chlorination process

Chlorination works by adding a chlorine-containing substance, such as chlorine gas or chlorine compounds, to the water. Chlorine is a powerful disinfectant that kills many types of harmful microorganisms through oxidation.

Chemical reaction

When chlorine is added to water, it reacts with it to form two other chemicals: hypochlorous acid (HOCl) and hypochlorite ions (OCl -). These are the active agents that work to purify water.

Cl2 + H2O ⇌ HOCl + HCl

Here's a visual example of how chlorine reacts with water:

Cl 2 + H 2 O HOCl + HCl

HOCl and OCl - work efficiently to inactivate microorganisms by penetrating their cell walls and disrupting their metabolism.

History of chlorination

The use of chlorine for water purification has been around since the early 20th century. The first major use of chlorination in the US was in Jersey City, New Jersey in 1908. Before its use, many people suffered from diseases such as typhoid fever due to contaminated water sources.

Chlorination substantially reduced the incidence of very serious waterborne diseases and was a major step toward improving public health. Today it is one of the most widely used methods for water purification worldwide.

Types of chlorination

Continuous chlorination

This is the most common type of chlorination, in which a steady and small amount of chlorine is added to the water supply. This ensures that water remains disinfected over time as it travels through pipes and storage systems.

Shock chlorination

In this method, a high concentration of chlorine is quickly added to the water supply to correct an immediate contamination problem or for initial system disinfection. This is important for emergencies, but is not used consistently because of its intensity.

Breakpoint chlorination

This process adds chlorine until all unwanted chemicals and bacteria are neutralized, reaching a "breakpoint" where free chlorine remains in the water, helping to control future contamination.

Benefits of chlorination

Chlorination is preferred for several reasons:

  • It is effective in killing a wide variety of germs that can cause diseases.
  • It provides residual protection, meaning it continues to purify water as it passes through the pipes.
  • It is cost effective and easy to implement in both small and large water systems.
  • Unlike some methods, chlorination can help remove undesirable tastes and odors in water.

Challenges and considerations

Although chlorination is highly effective, it still has some challenges:

  • It must be handled carefully as its high concentrations can be harmful to human health.
  • Chlorine can react with natural organic substances in water to form potentially harmful byproducts such as trihalomethanes (THMs).
  • Some microorganisms are more resistant to chlorine than others, so they need to be carefully monitored.
  • Communities must always balance the amount of chlorine with the taste and odor preferences of consumers.

Alternative water purification methods

Although chlorination is the most common method, there are other methods:

  • Filtration: This method physically removes dirt, debris and microorganisms from water.
  • Distillation: This purifies water by boiling it and then condensing the steam back into a liquid, leaving contaminants behind.
  • UV treatment: This method uses ultraviolet light to kill or inactivate microorganisms.
  • Ozonation: In this, ozone, an energetic form of oxygen, is used for disinfection and removal of impurities.

Each method has its benefits and limitations, and sometimes several methods are used together for best results.

Summary

Chlorination in water purification is a vital tool for ensuring safe drinking water. It efficiently kills harmful microbes and helps maintain clean water transported through pipes. Although there are some challenges associated with chlorination, its benefits far outweigh the concerns, making it a reliable method to help prevent waterborne diseases globally. Water purification methods like chlorination play an essential role in public health and safety, illustrating how chemistry affects everyday life.


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Chlorination in water purification

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