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 → Water and its importance ↓


Water as the universal solvent


Water is one of the most important substances on Earth. It is vital to all known forms of life and plays a vital role in both natural processes and human activities. One of its most important properties is its ability to act as a universal solvent. This means that water can dissolve more substances than any other liquid. To understand this unique feature of water, one must explore its chemical composition, the types of substances it dissolves, and its role in the environment.

Chemical composition of water

Water, chemically known as H2O, is composed of two hydrogen atoms covalently bonded to one oxygen atom. This simple molecular structure conceals a powerful feature - its polarity.

    H—O—H

The oxygen atom is more electronegative than the hydrogen atoms. This means that the oxygen atom pulls the shared electrons closer to itself, making it slightly negative, while the hydrogen atom becomes slightly positive. This charge separation makes water a polar molecule.

Below is a visual depiction of a water molecule demonstrating its polarity:

HeyHH

How water dissolves substances

The polarity of water allows it to effectively dissolve many different substances. When a substance is added to water, the positive and negative ends of the water molecules interact with the positive and negative ions of the substance. This interaction breaks the bonds holding the ions together, effectively dissolving the substance.

Example: Dissolving salt in water

Common table salt, or sodium chloride (NaCl), is an excellent example of a substance that dissolves well in water. Salt contains sodium ions (Na+) and chloride ions (Cl-). When salt is added to water, the negative oxygen ends of the water molecules are attracted to the sodium ions, and the positive hydrogen ends are attracted to the chloride ions. This attraction causes the ions to separate and diffuse into the water.

Na+CL-

Types of substances that dissolve in water

Water can dissolve a wide variety of substances, which can be broadly classified into two types: ionic compounds and polar covalent compounds.

Ionic compounds

Ionic compounds, such as salts, are composed of positively charged ions (cations) and negatively charged ions (anions). These ions are usually held together by strong ionic bonds. Water can dissolve ionic compounds efficiently because polar water molecules can surround and separate individual ions, allowing them to diffuse into the liquid.

Polar covalent compounds

Water can also dissolve polar covalent compounds, which have slight electrical charges that interact well with the polarity of water. A good example of this is sugar. Sugar dissolves in water because the polar regions of the sugar molecules interact with the polar water molecules, breaking up the structure of the sugar and causing it to mix more evenly with the water.

Substances that do not dissolve easily in water

While water is a versatile solvent, it is not effective with nonpolar substances, which lack the charges needed to interact with water's polar molecules. Nonpolar substances include oils and fats. These compounds do not dissolve because their molecules are not attracted to water molecules. Instead, they prefer to bond with other nonpolar molecules.

Oil MoleculeHHey

Importance of water as a universal solvent

Due to water's ability to dissolve various types of substances, it is essential for various biological, geological and chemical processes.

Biological significance

  • Transport of nutrients and wastes: In living organisms, water dissolves nutrients and carries them into cells, as well as dissolves wastes and carries them away. For example, in humans, blood, which is mostly water, carries oxygen, nutrients, and hormones to where they are needed in the body.
  • Cellular reactions: Many chemical reactions in biology occur in aqueous solutions. Water present in the cytoplasm of cells provides the medium for complex biochemical reactions that are essential for life.

Environmental and geological significance

  • Erosion and weathering: Water dissolves minerals from rocks, which contributes to soil formation. This process is part of the Earth's weathering and erosion cycle.
  • Climate regulation: Large bodies of water can absorb heat and help regulate the Earth's climate by storing this energy and slowly releasing it.

Chemical significance

  • Industrial solvent: Water is used as a solvent in many industrial processes, from the production of chemicals to the manufacture of foods.
  • Reaction medium: Many chemical reactions, especially in laboratory or industrial settings, rely on water as the medium for the interaction of reactants.

Conclusion

Water's role as a universal solvent is one of its most important characteristics, affecting life, the environment, and industry. Its ability to dissolve more substances than any other liquid makes it indispensable. By understanding how water interacts with different substances and its importance in various fields, we gain a greater appreciation for this extraordinary molecule.


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Water as the universal solvent

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