Is Matter Around Us Pure?
A pure substance is made up of only one type of particle and has uniform composition and properties. Common examples include sodium chloride and sugar. A mixture is a combination of two or more substances, where the individual components retain their own properties. Examples include air, soil, and sea water.
Types of Mixtures:
- Homogeneous (सजातीय ) Mixture: A mixture with uniform composition throughout (e.g., salt dissolved in water).
- Heterogeneous (विषमजातीय) Mixture: A mixture with non-uniform composition (e.g., soil, salad).
Solution is a homogeneous mixture consists of two components – solvent and solute.
- Solvent: The substance that dissolves the solute (present in larger quantity).
- Solute: The substance that dissolves in the solvent (present in smaller quantity).
Examples: Sugar + Water → Solute: Sugar, Solvent: Water, Tincture of Iodine → Solute: Iodine, Solvent: Alcohol, Soda Water → Solute: CO₂ (gas), Solvent: Water (liquid), Air → Solute: Oxygen, Solvent: Nitrogen
Types of Solutions:
- Solution (घोल): Stable homogeneous mixture; particle size < 1 nm (10⁻⁹ m); does not scatter light.
- Suspension (निलंबन): Heterogeneous; particles visible; particles settle down; e.g., chalk in water.
- Colloid (कोलॉइड): Intermediate particle size; scatters light (Tyndall effect); stable, Can’t filtered; e.g., Milk, fog, smoke, ink.
- Alloy (मिश्रधातु): Homogeneous solid solution of metals; cannot be separated physically; e.g., brass = Cu + Zn.
Characteristics of Solutions: Homogeneous mixture, Particle size < 1 nm, Do not scatter light (no Tyndall effect) Cannot be separated by filtration, Stable mixture; particles do not settle.
Concentration of a Solution:
- Mass by Mass % = (Mass of solute / Mass of solution) × 100
- Mass by Volume % = (Mass of solute / Volume of solution) × 100
- Volume by Volume % = (Volume of solute / Volume of solution) × 100
A colloid is a heterogeneous mixture where the particles are too small to be seen with the naked eye but large enough to scatter light. Shows Tyndall Effect – scattering of light due to colloidal particles. Colloidal particles are stable and do not settle down. Cannot be separated by filtration but can be separated by centrifugation. Colloids consist of two components:
- Dispersed Phase: The particles (like solute).
- Dispersion Medium: The medium in which particles are dispersed (like solvent).
| Type | Dispersed Phase | Dispersion Medium | Example |
|---|---|---|---|
| Aerosol | Liquid/Solid | Gas | Fog, smoke |
| Foam | Gas | Liquid/Solid | Shaving cream, sponge |
| Emulsion | Liquid | Liquid | Milk, cream |
| Sol | Solid | Liquid | Mud, paint |
| Gel | Liquid | Solid | Jelly, butter |
| Solid Sol | Solid | Solid | Gemstones, glass |
Physical and Chemical Changes
A physical change is a change in which the substance retains its original composition, and no new substance is formed. Examples: Ice melting, water boiling, butter melting. chemical change alters the chemical composition of a substance and results in the formation of a new substance.
Elements
An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction. Elements are classified into three types: metals, which are shiny, ductile, and good conductors (e.g., gold, copper, iron); non-metals, which are brittle, colored, and poor conductors (e.g., oxygen, carbon); and metalloids, which have properties of both (e.g., silicon, boron).
Q. Sodium chloride is best classified as: (A) Homogeneous mixture (B) Heterogeneous mixture (C) Pure substance (D) Compound mixture
Q. Which of the following is a pure substance? (A) Tap water (B) Soft drink (C) Sodium chloride (D) Air
Q. Which of the following is a homogeneous mixture? (A) Soil (B) Sugar in water (C) Oil and water (D) Sand and salt
Q. Which of the following is an example of a heterogeneous mixture? (A) Sugar solution (B) Salt in water (C) Soil (D) Air
Q. What is a key property of colloid? (A) Particles settle down (B) Particles visible to naked eye (C) Particles scatter light (D) Particles can be filtered
Q. Which one shows the Tyndall effect? (A) True solution (B) Suspension only (C) Colloid only (D) Both (B) and (C)
Q. Which of these expresses solution concentration? (A) Mass of solvent only (B) Volume of solute only (C) Mass of solute × 100 (D) (Mass of solute ÷ Mass of solution) × 100
Q. True solution particles are: (A) Visible to naked eye (B) Larger than 1 nm (C) Do not scatter light (D) Settle down on standing
Q. What type of solution is formed when no more solute can dissolve at a given temperature? (A) Dilute (B) Unsaturated (C) Concentrated (D) Saturated
Q. Which of the following statements is true about solutions? (A) Solute is always a solid (B) They scatter light strongly (C) Particle size is less than 1 nm (D) Solute can be seen through a microscope
Q. Which of the following mixtures shows the Tyndall effect? (A) Sugar solution (B) Salt solution (C) Milk (D) Alcohol
Q. What is the concentration (mass %) of a solution with 40g salt in 360g solution? (A) 12.5% (B) 11.11% (C) 10% (D) 15%
Q. Which technique is used to separate colloidal particles? (A) Filtration (B) Sedimentation (C) Centrifugation (D) Decantation
Q. Which combination forms an emulsion? (A) Solid in gas (B) Gas in gas (C) Liquid in liquid (D) Gas in solid
Q. What is true about a chemical change? (A) No new substance is formed (B) It is always reversible (C) Only physical state changes (D) A new substance is formed
Q. Which of the following is a metalloid? (A) Oxygen (B) Iron (C) Silicon (D) Gold