1. What is a Mixture?
A mixture contains more than one pure substance (elements or compounds) mixed in any proportion. For example, milk is a mixture of water, fat, and proteins, not a pure substance. Unlike pure substances (like sugar or sodium chloride), mixtures can be separated by physical methods like evaporation.
1.1 Types of Mixtures
- Homogeneous Mixtures (Solutions): Uniform composition throughout, e.g., salt in water or sugar in water. The particles are evenly mixed.
- Heterogeneous Mixtures: Non-uniform composition with visible parts, e.g., sand and salt, or oil and water.
Fun Activity: Mix some salt in water and try to separate it by evaporation. Compare it with mixing sand and water!
2. What is a Solution?
A solution is a homogeneous mixture of two or more substances. It has a solvent (major component) and a solute (minor component). Examples include lemonade (sugar in water), air (gases mixed), and alloys like brass (zinc and copper).
2.1 Properties of a Solution
- Uniform composition at the particle level.
- Particles are smaller than 1 nm, invisible to the naked eye.
- Does not scatter light (no Tyndall effect).
- Stable; solute doesn’t settle or separate by filtration.
2.2 Concentration of a Solution
Concentration measures how much solute is in a solution. Types include:
- Mass by Mass %: (Mass of solute / Mass of solution) × 100
- Mass by Volume %: (Mass of solute / Volume of solution) × руса
- Volume by Volume %: (Volume of solute / Volume of solution) × 100
2.3 Suspensions
A suspension is a heterogeneous mixture where particles are visible and settle over time, e.g., chalk in water. They scatter light and can be filtered.
2.4 Colloidal Solutions
A colloid is a heterogeneous mixture with particles too small to see but large enough to scatter light (Tyndall effect), e.g., milk or fog. Colloids are stable and require special separation like centrifugation.
Activity: Shine a torch through a glass of milk and a glass of salt water. Notice the Tyndall effect in milk!
3. Physical and Chemical Changes
Physical Changes: No change in chemical composition, only physical properties like shape or state change, e.g., melting ice or dissolving salt in water.
Chemical Changes: New substances are formed due to a change in chemical composition, e.g., burning wood or rusting iron.
Fun Fact: Burning a candle involves both physical (melting wax) and chemical (burning to produce gases) changes!
4. Types of Pure Substances
4.1 Elements
An element is a pure substance that cannot be broken down by chemical reactions, e.g., gold, oxygen. Elements are classified as:
- Metals: Shiny, conductive, malleable, e.g., copper, iron.
- Non-metals: Poor conductors, varied colors, e.g., carbon, oxygen.
- Metalloids: Properties of both, e.g., silicon, boron.
4.2 Compounds
A compound is a pure substance made of two or more elements chemically combined in a fixed ratio, e.g., water (H₂O). Compounds have different properties from their elements.
Activity: Mix iron filings and sulphur, then heat them. The heated mixture forms a compound with new properties!
Next Chapter
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