MATTER AROUND US

Pure Substances and Mixtures

  • Definition of Pure Substances:

    • Common understanding: no adulteration.

    • Scientific definition: substances with identical constituent particles.

  • Mixtures:

    • Consist of multiple pure substances.

    • Examples: milk (water, fat, proteins), seawater (salt and water).

  • Types of Mixtures:

    • Homogeneous Mixtures (Solutions):

      • Uniform composition (e.g., saltwater, sugar in water).

      • Can have variable composition.

    • Heterogeneous Mixtures:

      • Non-uniform parts (e.g., oil and water, sand and iron filings).

Activities on Mixtures

  • Activity 1: Observation of uniformity in colored solutions of varying concentrations.

    • Groups A & B: Homogeneous mixtures with different shades of copper sulfate solution.

    • Groups C & D: Heterogeneous mixtures showing distinct particles.

Properties of Mixtures

  • Homogeneous Mixtures:

    • Composition uniform at the particle level.

    • Particles cannot be seen and do not scatter light.

  • Heterogeneous Mixtures:

    • Particles are visible and can be separated by filtration.

    • Examples include suspensions and colloidal solutions.

Solutions, Suspensions, and Colloids

  • Solutions:

    • Homogeneous mixtures of solute and solvent.

    • Example: lemonade (sugar and water).

  • Suspensions:

    • Heterogeneous mixtures with visible particles.

    • Example: chalk powder in water.

  • Colloids:

    • Milky appearance due to small particle size; scatter light (Tyndall effect).

    • Examples: mist, milk, smoke.

Properties of Solutions, Suspensions, and Colloids

  • Solutions:

    • Particles < 1 nm, stable, cannot be filtered.

  • Suspensions:

    • Particles settle upon standing, can be filtered.

  • Colloids:

    • Stable with no settling, particles scatter light.

Concentration of Solutions

  • Dilute, concentrated, and saturated solutions based on solute amount.

  • Saturated Solution: Maximum solute dissolved at a given temperature.

Pure Substances Classification

  • Elements:

    • Cannot be chemically broken down (e.g., metals and non-metals).

  • Compounds:

    • Two or more elements chemically combined in fixed ratios (e.g., water, sodium chloride).

Key Points

  • Mixtures: Easier to separate than compounds, retain properties of components.

  • Compounds: Fixed composition, properties differ from individual elements.

  • Chemical vs. Physical Changes:

    • Physical changes: do not alter chemical composition (e.g., phase changes).

    • Chemical changes: result in new substances (e.g., burning).