Class 9th || Science || Notes || Chapter 2: Is Matter Around Us Pure?

Chapter 2: Is Matter Around Us Pure?

1. Introduction to Pure Substances and Mixtures:

• Pure Substances: Consists of a single type of particle. Examples include elements (like gold, and oxygen) and compounds (like water, and sodium chloride).
• Mixtures: Consist of two or more substances mixed together but not chemically combined. Examples include air, saltwater, etc.

2. Types of Mixtures:

• Homogeneous Mixtures: Have a uniform composition throughout. Also known as solutions. Example: salt dissolved in water.
• Heterogeneous Mixtures: Have a non-uniform composition. Example: sand in water.

3. Solutions:

• Definition: A homogeneous mixture of two or more substances.
• Components:
  • Solvent: The substance in which the solute is dissolved (e.g., water in a saltwater solution).
  • Solute: The substance that is dissolved (e.g., salt in a saltwater solution).
• Properties of Solutions:
  • Particles are very small (less than 1 nanometer).
  • Do not scatter light.
  • Cannot be separated by filtration.
  • Stable, do not separate on standing.
• Concentration of Solutions:
  • Can be expressed in terms of mass by mass percentage, mass by volume percentage, etc.

4. Colloids:

• Definition: A mixture where very small particles of one substance are evenly distributed throughout another substance.
• Properties of Colloids:
  • Particles are intermediate in size (between 1 nanometer and 1000 nanometers).
  • Scatter light (Tyndall effect).
  • Cannot be separated by filtration but can be separated by centrifugation.
• Examples: Milk, fog.

5. Suspensions:

• Definition: A heterogeneous mixture where the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
• Properties of Suspensions:
  • Particles are larger than 1000 nanometers.
  • May scatter light but are not transparent.
  • Particles can be seen with the naked eye.
  • Unstable, particles settle on standing.
  • Can be separated by filtration.
• Examples: Muddy water, sand in water.

6. Separating the Components of a Mixture:

• Physical Methods of Separation:
  • Filtration: Used to separate an insoluble solid from a liquid.
  • Evaporation: Used to separate a soluble solid from a liquid.
  • Centrifugation: Used to separate suspended particles from a liquid in which the particles are small and insoluble.
  • Sublimation: Used to separate substances that sublime from those that do not.
  • Chromatography: Used to separate different dissolved constituents of a mixture.
  • Distillation: Used to separate mixtures of miscible liquids with different boiling points.

7. Elements and Compounds:

• Elements: Pure substances that cannot be broken down into simpler substances by chemical means. Examples: Iron (Fe) and oxygen (O₂).
• Compounds: Pure substances composed of two or more elements chemically combined in a fixed proportion. Examples: Water (H₂O) and carbon dioxide (CO₂).

Conclusion: The chapter provides a comprehensive understanding of the different types of substances and mixtures, their properties, and various methods to separate the components of mixtures. It lays the foundation for understanding the nature of matter and its composition, which is crucial for further studies in chemistry.