Is Matter Around Us Pure?
Mixtures, solutions, suspensions, colloids, and separation techniques.
Chapter Overview
Pure substances have fixed composition; mixtures contain two or more components physically combined. You learn types of mixtures, separation techniques, solutions, suspensions, colloids, and concentration expressions.
Pure vs Mixture
- Element: one type of atom (Cu, O₂)
- Compound: two+ elements chemically combined (H₂O, NaCl)
- Homogeneous mixture: uniform composition (salt solution)
- Heterogeneous mixture: non-uniform (sand + water)
Concentration
Mass %
Mass % = (mass of solute / mass of solution) × 100
Volume %
Volume % = (volume of solute / volume of solution) × 100
Separation Techniques
- Filtration, evaporation, centrifugation
- Distillation (fractional for miscible liquids)
- Chromatography, separating funnel, crystallisation
Colloids & Tyndall Effect
- Colloid particle size: 1 nm – 1000 nm
- Tyndall effect: scattering of light by colloidal particles
- Examples: milk, fog, starch solution
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Mass percentage
5 g sugar dissolved in 95 g water. Find mass %.
- 1Solution mass = 5 + 95 = 100 g
- 2Mass % = (5/100) × 100
Answer
5%
Identify mixture type
Classify: air, muddy water, brass.
- 1Air: homogeneous (gaseous solution)
- 2Muddy water: heterogeneous suspension
- 3Brass: homogeneous solid solution (alloy)
Answer
Air & brass homogeneous; muddy water heterogeneous
Key Points to Remember
- ✓ Alloys are homogeneous mixtures of metals
- ✓ Suspensions settle on standing; colloids do not
- ✓ Physical methods separate mixtures, not compounds
Exam Tips
- • Know examples of each separation method
- • Distinguish solution, suspension, colloid in tabular form
- • Show calculation steps for concentration
Practice MCQs — Is Matter Around Us Pure?
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Brass is a mixture of: