Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Solutions and Solubility ↓


Concept of osmosis and reverse osmosis


Introduction to osmosis

Osmosis is a fundamental concept in chemistry that involves the movement of water across a semipermeable membrane. It is a type of passive transport, meaning it does not require energy to occur. In osmosis, water moves from an area of low solute concentration to an area of high solute concentration until equilibrium is reached.

Imagine a simple experiment where you have a container divided by a semipermeable membrane. One side has pure water, and the other side has a sugar solution. Osmosis will cause water molecules to move from the pure water side to the sugar solution side to try to equalize the concentration of water on both sides.

pure water sugar paste semipermeable membrane

Theory of osmosis

The driving force behind osmosis is the concentration gradient of water across a semipermeable membrane. Here are the main principles:

  • Concentration gradient: Water moves from areas of low solute concentration (high water concentration) to areas of high solute concentration (low water concentration).
  • Semipermeable membrane: A membrane that allows some molecules or ions to pass through it by diffusion and sometimes facilitates the active transport of other molecules.
  • Equilibrium: Osmosis continues until the concentrations on either side of the membrane are equal, at which point equilibrium is achieved.

Osmosis text example

Consider a red blood cell placed in pure water. There is much more solute inside the cell than in the surrounding water. Water will enter the cell via osmosis. If too much water enters, the cell can burst. This is why IV solutions must be isotonic with the blood.

Reverse osmosis

Reverse osmosis (RO) is the process of forcing water through a semipermeable membrane, but in the opposite direction of natural osmosis. This process requires external pressure to move water from an area of high solute concentration to an area of low solute concentration. Reverse osmosis is commonly used for water purification, desalination, and removal of contaminants from drinking water.

salt water pure water Pressure Applied RO Membrane

Principles of reverse osmosis

While natural osmosis occurs due to a concentration gradient, reverse osmosis requires pressure. Here are the main principles:

  • External pressure: Pressure is applied to the region of higher concentration to force water through a semipermeable membrane to the region of lower concentration.
  • Semipermeable membrane: In RO, the membrane is designed to allow water to pass through, while it prevents contaminants such as salts and impurities from passing through.
  • Purification: As water is forced through the membrane, impurities are left behind, resulting in pure water on the other side.

Text example of reverse osmosis

Consider a scenario where salty seawater needs to be converted into drinkable water. Reverse osmosis can be used by pressurizing seawater and forcing it through a membrane that traps the salt but allows water molecules to pass through. This leaves the salt behind and results in fresh water.

Applications of osmosis and reverse osmosis

The concepts of osmosis and reverse osmosis have wide applications in scientific, industrial, and everyday contexts:

Applications of osmosis

  • Biology: Osmosis is important in the transport of water and nutrients in plants and animals. It helps maintain cell structure and regulate fluid balance.
  • Food preservation: Salt or sugar is used to remove water from food by osmosis, which helps prevent bacterial growth.

Applications of reverse osmosis

  • Water purification: RO is widely used in water treatment systems to remove contaminants and make water drinkable.
  • Desalination: RO is used to convert seawater into freshwater in water-scarce areas.
  • Industrial processes: RO can remove impurities for manufacturing, such as pharmaceuticals or food and beverage production.

Summary

Osmosis and reverse osmosis are important concepts in understanding how water interacts with solutes across membranes. Osmosis allows solute concentrations to equalize naturally, while reverse osmosis requires an external force to achieve purification, making it invaluable for a variety of industrial and everyday processes.


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Saturated, unsaturated and supersaturated solutions
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Concept of osmosis and reverse osmosis

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