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 → Separation of mixtures → Separation methods ↓


Evaporation


Evaporation is a common method of separating mixtures, often used to separate dissolved solids from liquids. This process occurs naturally and plays an important role in the water cycle in nature. In chemistry and various applications, evaporation is a technique used to obtain solids, such as salts, from solutions.

Understanding evaporation

Evaporation is the process by which molecules in the liquid state spontaneously change to the gas state. It occurs at the surface of the liquid, below its boiling point. Unlike boiling, which occurs throughout the liquid at a specific temperature and pressure, evaporation occurs at the surface and can occur at any temperature.

How vaporization works

When the molecules in a liquid gain enough energy, they overcome the forces holding them in the liquid state and escape into the air as a gas. The energy comes from heat; it doesn't have to be intense heat—sometimes just room temperature is enough to cause vaporization.

Example: When you leave a glass full of water on the table, over time the water will evaporate, even if it is not boiling.

Examples of evaporation in daily life

Evaporation can be observed in many everyday situations:

  • Drying clothes in the sun.
  • The disappearance of rainwater over time.
  • Water disappears from wet surfaces.
  • The wet soil is drying in the sunlight.

Evaporation in the water cycle

Evaporation is a key process in the water cycle, in which water from oceans, lakes and rivers turns into water vapor and rises into the atmosphere. This vapor eventually forms clouds and falls back as precipitation, continuing the cycle.

Example:
Ocean water + Sun’s heat → Water vapor

Uses of evaporation in chemistry

In chemistry laboratories, evaporation is commonly used to separate the solvent from the solute. When a solution is heated, the solvent, usually water, evaporates, leaving the solute behind. This method helps to obtain the pure solute from the solution.

Example of a laboratory experiment

If the salt water solution is heated, the water evaporates and the salt crystals are left behind. Here's a simple step-by-step:

  1. Pour the salty water solution into a shallow dish.
  2. Place the pot in a warm, sunny location or provide heat using a burner.
  3. As the water evaporates, salt crystals begin to form at the bottom of the pot.

Pros and cons of vaporization

Advantages of vaporization

  • Simple and easy execution.
  • No additional chemicals required.
  • Useful in drying processes and in removing solids from solutions.

Limitations of evaporation

  • Time consuming, especially without heat.
  • Not efficient for large quantities of liquid.
Chemical formula of salt in water:
NaCl (in H 2 O) → Na + + Cl -

Factors affecting evaporation

Several factors can affect the rate of evaporation:

Temperature

Higher temperatures give the molecules more energy, increasing the rate of evaporation. This is why clothes dry faster in hot sun than on a cloudy day.

Surface area

The larger the surface area of the liquid, the faster the evaporation. Spreading the solution over a larger area can speed up the process.

Damp

Evaporation is slower under high humidity conditions, because there is already a lot of water vapor in the air, slowing the rate at which additional molecules evaporate.

Illustration of the evaporation process

Consider the following simplified illustration that shows how evaporation separates the solute from the solvent:

Imagine a container filled with a salt water solution:
Salt water solution

Over time, or with the application of heat, the liquid level drops as the water evaporates, leaving behind salt crystals:
Leftover water and salt Salt crystals

Applications of evaporation

In the industry

Evaporation is used in a variety of industries:

  • Salt production: Salt is often extracted from seawater through large-scale evaporation.
  • Food processing: It is used to concentrate flavors, remove water from liquids, and preserve food.
  • Chemical manufacturing: Used to separate chemicals and minerals.

In agriculture

Farmers use evaporation to dry grains and other crops quickly and prevent them from spoiling.

Conclusion

Evaporation is a natural but powerful process that has versatile applications in science and industry. Understanding evaporation involves recognizing its role in nature, its wide range of applications, and its importance in separating mixtures. By mastering this knowledge, one can appreciate the utility of this simple but important process in a variety of fields.


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Sedimentation and decantation
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Evaporation

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