Class IX SEBA Science – Chapter 2: Is Matter Around Us Pure?
Class IX SEBA Science – Chapter 2: Is Matter Around Us Pure?
🧪 1. What is a Mixture?
- A mixture is a combination of two or more substances that are physically mixed but not chemically combined.
- Components retain their individual properties.
- Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform).
🔍 2. Types of Mixtures
- Homogeneous mixture → One phase; uniform throughout (e.g., salt in water).
- Heterogeneous mixture → More than one phase; visible components (e.g., oil in water).
🧫 3. What is a Solution?
- A solution is a homogeneous mixture of two or more substances.
- Solvent: The component in larger amount.
- Solute: The component in lesser amount.
- Properties:
- Uniform appearance
- Particles smaller than 1 nm (not visible)
- Stable; doesn’t settle down
- Cannot be filtered
📏 4. Concentration of a Solution
- Concentration = Amount of solute dissolved in a given amount of solvent.
- Can be expressed as:
- Mass by mass % = (mass of solute / mass of solution) × 100
- Mass by volume % = (mass of solute / volume of solution) × 100
🌫️ 5. What is a Suspension?
- A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid or gas.
- Properties:
- Visible particles
- Unstable; particles settle
- Can be filtered
- Scatters light (Tyndall effect)
💧 6. What is a Colloid?
- A colloid is a mixture where particles are intermediate in size between solutions and suspensions.
- Properties:
- Appears homogeneous to naked eye but is actually heterogeneous
- Particles don’t settle
- Cannot be filtered
- Shows Tyndall effect
🧪 7. Separation of Components of a Mixture
- Evaporation: To recover solids from a solution (e.g., salt from salt water).
- Centrifugation: To separate heavier and lighter components in liquids (e.g., cream from milk).
- Decantation and filtration: For solid-liquid heterogeneous mixtures.
- Sublimation: Separates sublimable solids (e.g., camphor).
- Chromatography: Separates colored components of a mixture.
- Distillation: For liquid mixtures with different boiling points.
- Separating funnel: For immiscible liquids (e.g., oil and water).
🧪 8. What are Pure Substances?
- Pure substances consist of only one type of particle.
- Two types:
- Elements: Cannot be broken down (e.g., iron, oxygen)
- Compounds: Formed by chemical combination of elements (e.g., water, CO₂)
📘 Exercise Questions and Answers
1. Which of the following are pure substances?
a) Ice → ✅ Yes
b) Milk → ❌ No
c) Iron → ✅ Yes
d) Hydrochloric acid → ✅ Yes
e) Calcium oxide → ✅ Yes
f) Mercury → ✅ Yes
g) Brick → ❌ No
h) Wood → ❌ No
i) Air → ❌ No (mixture)
2. Identify the solutions among the following:
a) Soda water → ✅
b) Wood → ❌
c) Air → ✅
d) Soil → ❌
e) Vinegar → ✅
3. Write the characteristics of particles of matter.
- They have space between them
- They are constantly moving
- They attract each other
4. Tyndall effect is shown by which type of mixture?
- Colloids show Tyndall effect.
5. Classify the following as physical or chemical change:
a) Cutting of trees → Physical
b) Melting of butter → Physical
c) Rusting of almirah → Chemical
d) Boiling of water → Physical
e) Digestion of food → Chemical
f) Freezing of water → Physical
6. Which separation technique will you apply for the following:
a) Sodium chloride from its solution in water → Evaporation
b) Camphor from salt → Sublimation
c) Cream from milk → Centrifugation
d) Iron from sand → Magnetic separation
e) Oil from water → Separating funnel
f) Dye from black ink → Chromatography
✍️ Extra Important Questions with Answers
1. What is the Tyndall effect?
The scattering of light by particles in a colloid or in a very fine suspension is called Tyndall effect.
2. How can you separate salt from salt solution?
By evaporation, water evaporates leaving salt behind.
3. Why is air a mixture and not a compound?
Air contains multiple gases like nitrogen, oxygen, and carbon dioxide that can be separated physically, and their ratio can vary.
4. Define solubility.
Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature.
5. Why is milk considered a colloid?
Milk has microscopic fat globules dispersed in water, which do not settle and show the Tyndall effect.
proceed to Chapter 3: Atoms and Molecules?
