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 → Separation Techniques ↓


Filtration, Sedimentation and Decantation


Introduction

In chemistry, separation of substances is an important process used to separate mixtures into their components. In Class 8, you are introduced to several basic techniques of separation that help us purify substances or obtain useful components from a mixture. The three basic techniques are filtration, sedimentation, and decantation. Understanding these processes helps us understand how mixtures can be sorted into pure substances so that they can be used in everyday life or complex industries.

Filtration

Filtration is a separation technique used to separate solids from liquids or gases, using a filter medium that allows the liquid to pass through but not the solid. The solid that remains on the filter is called the residue, while the liquid that passes through is called the filtrate.

Imagine you have a mixture of sand and water. To separate the sand from the water, you can use a simple filtration process.

a mixture of water and sand filter paper Sand

Example: Filtration is used in water purification plants, where dirty water is passed through a filter, removing suspended particles, thus obtaining clean water.

Filtration is used in our daily life in making coffee. The filter allows the liquid coffee to pass through while keeping the coffee residue aside.

How Filtration Works

This process depends on the difference in the size of the particles to be separated. Typically, filter paper or similar porous material is used as the filter medium. The mixture is poured onto the filter paper in a funnel. The larger particles are trapped by the pores of the filter, while the liquid passes through it. Here are the simple steps:

  1. Pour the mixture into a funnel lined with filter paper.
  2. Allow the liquid to seep through the paper, leaving the solids behind.
  3. The clear liquid collected is called filtrate.
  4. The solid matter trapped on the filter paper is called the residue.

Sedimentation

Sedimentation is the process by which heavier particles in a mixture settle at the bottom of a container without being stirred for some time. It is based on the principle that solids are denser than liquids. Consider a scenario where you mix soil with water. If left stationary, you will observe that the soil slowly settles at the bottom of the container due to gravity.

A mixture of soil and water Frozen soil

Example: Sedimentation can be seen in natural environments such as rivers and lakes, where soil and other particles slowly settle to the bottom over time.

How Sedimentation Works

When a suspension of solid particles in a liquid is allowed to settle, the particles tend to settle to the bottom due to their weight and gravitational force. As the particles settle, the clarity of the water above increases. The clear water above the settled solid is often called the supernatant.

  1. Mix solids and liquids thoroughly in a container.
  2. Let the mixture sit for several hours or until the solids settle.
  3. The solids will form a layer at the bottom, and a clear liquid will form on top.

Decantation

Decantation is a method of separating mixtures by removing a layer of liquid, usually the layer from which a precipitate has settled. After sedimentation, the clear liquid can be poured over the deposit of solid, which is called the decantation.

Decanting process Clean water Frozen soil

Example: We often use draining in everyday life. For example, when we cook rice and want to remove excess water from it after boiling, the water is drained from the boiled rice.

How Decanting Works

Once the solid particles have settled through sedimentation, decantation can be used to remove the liquid without disturbing the settled solid. The key is to slowly pour the top layer of liquid away from the container.

  1. When sedimentation is complete and the solids have settled, prepare to add the liquid.
  2. Gently tilt the container to allow the liquid to drain out without damaging the solid part at the bottom.
  3. Continue until most of the liquid has drained out.

Conclusion

Filtration, sedimentation, and decantation are three simple but effective methods of separating mixtures into their components. Each method relies on different principles: filtration uses size differences, sedimentation uses density differences, and filtration uses the separation achieved by sedimentation. These techniques are not only applied in academic settings, but are also widely used in everyday life and many industrial processes.

These separation techniques are fundamental in chemistry and provide a basic understanding of how different substances can be separated and used efficiently in various applications.


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Filtration, Sedimentation and Decantation

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