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 ↓


Evaporation and crystallization


In the world of chemistry, the process of separating substances is important in both the laboratory and real-world applications. Two important methods used in separating mixtures are evaporation and crystallization. These processes are often used to obtain pure substances from mixtures, taking advantage of the different properties of the components in the mixture.

Understanding evaporation

Evaporation is the process in which a liquid changes into a vapor. It occurs when the molecules of the liquid gain enough energy to break free from the surface and become a gas. Evaporation occurs faster when the temperature is high or when the liquid has a large surface area.

For example, if you spill water on the floor and leave it in the sun, the water will eventually disappear due to evaporation. The sun provides energy that heats water molecules, causing them to escape into the air as water vapor.

energy

Application of evaporation in separation techniques

Evaporation is useful in separating a soluble solid from a liquid. For example, take a solution of salt in water. When you heat the solution, the water will evaporate, and the salt will be left behind as the temperature rises.

Here's how you can use evaporation to separate salt from water:

  1. Pour the salty water solution into a shallow dish.
  2. Gently heat the pot using a Bunsen burner or leave it in the sun.
  3. As the water evaporates, you will start to see salt crystals form at the bottom of the pot.
  4. When all the water has evaporated, collect the dry salt crystals.

Chemical aspect of evaporation

Chemically, during evaporation, there is no change in the chemical composition of the liquid. The initial liquid simply changes its state to gas. For example, H 2 O (liquid) turns into H 2 O (gas) after evaporation.

Understanding crystallization

Crystallization is another technique used to form solid crystals from a solution. Unlike evaporation, which focuses on the removal of the liquid, crystallization emphasizes the formation of a crystal structure from a solution that contains a solute.

Imagine that you are mixing sugar in water. You will notice that after some time the sugar stops dissolving, no matter how much you stir. The solution has become saturated. If you cool this saturated solution or allow it to evaporate slowly, sugar crystals will begin to form.

Water solute Crystal hot/cold

Steps of simple crystallization

A simple method of crystallisation using a sugar solution is as follows:

  1. First, prepare a solution of water and sugar in which the sugar stops dissolving.
  2. Heat the solution slowly until it begins to simmer (be careful not to let it boil).
  3. Allow the solution to cool slowly without stirring it.
  4. As it cools, sugar crystals will begin to form at the bottom.
  5. When all the crystals are visible, carefully pour off the remaining solution, so that only the crystals remain.

The chemistry behind crystallization

Crystallization involves the formation of a crystal structure. In essence, it is the ordered geometric packing of atoms, ions, or molecules. As the solution cools or evaporates, the solute particles come closer and attract each other, forming bonds that form the crystal lattice.

In terms of practical chemistry, this can be represented as:

        C 12 H 22 O 11 (aq) → C 12 H 22 O 11 (s)

Combination of evaporation and crystallization

Often, evaporation and crystallization are used together in industries to make pure substances from solutions. For example, in the production of salt, seawater is pumped into large shallow open ponds, where the sun promotes evaporation. As the water evaporates, the solution becomes saturated, and the salt precipitates as crystals that can be collected and refined.

sea water Salt crystals

Examples of evaporation and crystallization in real life

  • Salt Making - As mentioned, the production of salt from seawater is a combination of evaporation followed by crystallization.
  • Sugar manufacturing - Sugar is extracted from sugar cane or beet juice and crystallized.
  • Purification of solids - It is used in chemical laboratories to obtain high purity solid compounds.

Conclusion

Both evaporation and crystallization are fundamental chemical techniques that take advantage of the different physical properties of materials to separate mixtures. Whether it's extracting salt from seawater or purifying substances in the laboratory, these processes are vital tools for scientists and industry professionals around the world.


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Filtration, Sedimentation and Decantation
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Evaporation and crystallization

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