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


In chemistry, we often deal with mixtures. A mixture is a combination of two or more substances where each substance retains its chemical identity. Sometimes, we need to separate a mixture into its individual components, either to analyze it more precisely or to use different parts of it. These processes are known as separation techniques.

Separation techniques involve separating a mixture into its components and removing impurities. In Class 8 Chemistry, we learn some basic methods of separating simple mixtures. Various methods are available, and the choice of method depends on the nature of the mixture and the properties of its components.

Types of mixtures

Before getting into the separation techniques, it is important to understand the types of mixtures. There are broadly two types:

  • Homogeneous mixture: The structure is uniform throughout, such as salt dissolved in water.
  • Heterogeneous mixture: The composition is not uniform, such as a mixture of sand and iron filings.

Basic separation techniques

Let's look at some of the basic separation techniques that are commonly used.

Filtration

Filtration is used to separate insoluble solids from liquids. In this method, the mixture is passed through a filter. The liquid remains on the filter paper while the solid remains on the filter paper.

Example: Separating sand from a mixture of sand and water. In this case, the sand is the solid that gets trapped in the filter paper, and the water is the liquid that passes through it.

Evaporation

Evaporation is a technique in which a soluble solid is separated from a liquid. By heating the mixture, the liquid evaporates, leaving a residue of the solid behind.

Example: Obtaining salt from a saline solution by heating. As the water evaporates, salt crystals remain.

Distillation

Distillation is used to separate a mixture of two or more liquids with different boiling points. The mixture is heated, and the component boiling at the lowest temperature evaporates first. The vapor is then cooled and collected as a liquid.

Example: Purifying water from impurities or separating alcohol from an alcohol-water mixture.

Centrifugation

Centrifugation involves spinning the mixture at very high speeds. The centrifugal force causes denser particles to move outward and settle to the bottom, separating them from less dense matter.

Example: Separating cream from milk.

Magnetic separation

Magnetic separation is a method for separating solid-solid mixtures of magnetic and non-magnetic substances.

Example: Removing iron pieces from sand using a magnet. The iron pieces get attracted to the magnet, leaving the sand behind.

Chromatography

Chromatography is a technique by which a mixture of dissolved solids is separated. It consists of a stationary phase and a mobile phase. As the mixture moves along the mobile phase, its components are separated based on their different affinities for the stationary phase.

Example: Separating different colours in a dye.

Sifting

Sieving is a method of separating particles based on their size, using a mesh or net to separate larger particles from smaller ones.

Example: Separating the grain from the chaff.

Decantation

Decantation is used to separate a liquid from an insoluble solid or two immiscible liquids. This process involves pouring off the upper layer without disturbing the lower layer.

Example: Removing water from a mixture of sand and water.

Visual example: filtering sand and water

In the visualization, a mixture of sand (black particles) and water (blue) is poured through filter paper (grey). The sand is left in the filter while the water collects in the container below.

Chemistry in everyday life

Many of the separation techniques discussed are used in everyday life.

  • In the kitchen: Using a sieve to sift flour or wash vegetables.
  • Water purification: Filters to purify drinking water.
  • Oil refining: Distillation to separate different fuel products.
  • In laboratories: Chromatography for the analysis of substances.

Conclusion

Separation techniques are important in both everyday tasks and industrial processes. They allow us to purify substances, analyze compositions, and break down mixtures into their component parts. Understanding the principles and applications of these techniques is a fundamental part of chemistry.

By mastering these techniques, students can appreciate the complexity and diversity of solutions and mixtures found in both natural and man-made environments.


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Separation Techniques

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