NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure
NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure covers pure substances, mixtures, true solutions, suspensions, colloids, Tyndall effect, physical and chemical changes, elements, compounds, and separation techniques.
Overview of Topics & Subtopics (Click to Jump)
1. Pure Substances vs. Mixtures
Short Note:
• Pure Substance: Consists of a single type of particle with fixed physical and chemical properties (e.g., Gold, Pure Water, Salt).
• Mixture: Constituted by more than one kind of pure form of matter, combined in any ratio.
- Homogeneous Mixture: Has a uniform composition throughout (e.g., salt in water, air, alloys).
- Heterogeneous Mixture: Has non-uniform composition with physically distinct parts (e.g., oil in water, sand in salt).
2. Solutions, Suspensions, and Colloids (Tyndall Effect)
Short Note:
• True Solution: Homogeneous mixture; particle size < 1 nm; stable; does not scatter light (no Tyndall effect).
• Suspension: Heterogeneous mixture; particle size > 100 nm; unstable (particles settle down); scatters light when particles are suspended.
• Colloid: Appears homogeneous but is heterogeneous; particle size between 1 nm and 100 nm; stable; scatters light (shows Tyndall effect, e.g., milk, fog, starch solution).
• Concentration of Solution: Mass percentage = (Mass of Solute / Mass of Solution) × 100.
3. Physical and Chemical Changes
Short Note:
• Physical Change: Reversible or temporary change where no new substance is formed; only physical properties like shape, state, or volume change (e.g., melting of ice, cutting wood, dissolving salt).
• Chemical Change: Irreversible or permanent change in which new substances with entirely different properties are formed (e.g., rusting of iron, burning of paper, digestion of food).
4. Types of Pure Substances: Elements & Compounds
Short Note:
• Element: Basic form of matter that cannot be broken down into simpler substances by chemical reactions (classified into Metals, Non-metals, and Metalloids).
• Compound: Substance composed of two or more elements chemically combined in a fixed proportion by mass (e.g., H2O, CO2).
• Mixture vs. Compound: Mixtures contain components physically mixed with variable composition; Compounds contain elements chemically bonded with fixed composition.
Intext Questions - Page Number: 15
• Homogeneous Mixture: Has a uniform composition throughout, no visible boundaries of separation (e.g., sugar solution, brass).
• Heterogeneous Mixture: Has a non-uniform composition throughout, with visible boundaries between components (e.g., mixture of salt and iron filings, muddy water).
Intext Questions - Page Number: 18
1. Solution: Homogeneous, particle size < 1 nm, stable, transparent, does not scatter light.
2. Sol (Colloid): Heterogeneous, particle size 1–100 nm, stable, translucent, scatters light (Tyndall effect).
3. Suspension: Heterogeneous, particle size > 100 nm, unstable, opaque, scatters light until particles settle down.
Textbook Chapter End Exercise Questions
• Ice (Compound - H2O)
• Iron (Element - Fe)
• Hydrochloric acid (Pure chemical solution/compound in pure gas state)
• Calcium oxide (Compound - CaO)
• Mercury (Element - Hg)
• Physical Changes: (a) Cutting of trees, (b) Melting of butter in a pan, (d) Boiling of water to form steam, (f) Dissolving common salt in water, (g) Making a fruit salad with raw fruits.
• Chemical Changes: (c) Rusting of almirah, (e) Passing of electric current through water to form hydrogen and oxygen, (h) Burning of paper and wood.
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.