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 ↓


reverse osmosis


Reverse Osmosis (RO) is an important technology used in water purification. It is a modern and effective method for removing unwanted impurities, salts and contaminants from water to make it clean and drinkable. Reverse Osmosis can be much easier to understand if we break it down into parts and use some simple examples.

What is reverse osmosis?

Reverse osmosis is a process where water is forced through a special membrane using pressure that filters out impurities. This process removes dissolved particles, bacteria, ions, and even some minerals found in tap water. Let’s think of it like a very fine sieve that allows only clean water molecules to pass through, leaving all the dirty substances behind.

Visual example of reverse osmosis

impure water pure water Membrane Impurities left behind

How does reverse osmosis work?

To understand how reverse osmosis works, we first need to know what osmosis is. Osmosis is the process in which water moves from a low concentration solution to a more concentrated solution through a semi-permeable membrane. The goal is to balance the concentrations on both sides of the membrane.

Osmosis example

Imagine you have two glasses filled with water. We put a slice of cucumber in one glass. Over time, the water in the glass without the cucumber decreases as water molecules move through the skin of the cucumber (acting like a membrane) to balance the concentrations. This is osmosis!

Now, reverse osmosis is just the opposite. In reverse osmosis, we pressurize more concentrated water, pushing it through a membrane that traps impurities and allows only clean water to pass through.

Chemical representation

A simple equation to illustrate this concept is as follows:

Pressure + H2O (impure) → Membrane → H2O (pure) + Impurities

The importance of reverse osmosis

  1. Drinking water purification: Reverse osmosis is widely used to purify tap water in homes, making it safe for drinking and cooking. This technology is even more important in areas where water quality is poor.
  2. Industrial uses: Industries require pure water for various processes. This ensures that machinery runs smoothly and products remain free from contamination.
  3. Aquariums: Fish need a clean environment to thrive, and reverse osmosis can remove harmful chemicals present in tap water.
  4. Food and beverage industry: Pure water is required for the production of beverages such as bottled water and soft drinks. Reverse osmosis is a cost-effective solution that ensures consistency in taste and quality.

Parts of a reverse osmosis system

Understanding the parts of an RO system can help to understand how it works:

  • Pre-filters: These are used to remove larger particles such as dirt, rust and sediment that can damage the membrane.
  • Reverse osmosis membrane: This is the heart of the RO system, responsible for filtering the water.
  • Post-filters: These ensure that any residual taste or odor is removed from the water, resulting in better water quality.
  • Storage tank: Once the water is filtered, it is stored so that it can be used when required.

Visual representation of a reverse osmosis system

Pre-Filter RO Membrane Post-Filter storage tank

Benefits of using reverse osmosis

  • Healthy living: It removes harmful substances such as lead, mercury, fluoride and chlorine, making water healthier to drink.
  • Environmental protection: Helps reduce dependency on bottled water, minimising plastic waste.
  • Cost-effective: Although the initial installation cost may be high, operating an RO system is cheaper than purchasing bottled water.
  • Improved taste and odor: Removing impurities improves the taste and odor of water.

Challenges and considerations

As useful as reverse osmosis is, there are some challenges and considerations to be aware of:

  • Wastewater: RO systems can waste a large amount of water during the purification process.
  • Maintenance: Regular checks and maintenance are required to ensure the efficiency of the system.
  • Mineral removal: Beneficial minerals may also be removed, which may require additional supplementation in the diet.

Conclusion

Reverse osmosis is a vital technology in our quest for clean, healthy and safe water. Whether in our homes, industries or aquariums, it provides a reliable way to filter harmful contaminants from water, ensuring that what we drink is as pure as possible. Understanding the process, benefits and challenges of reverse osmosis can enable us to make informed decisions about how we get our water and helps us appreciate the processes that keep our water clean.


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