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NCERT Solutions for Class 9th Science Chapter 5 Exploring Mixtures and their Separation

Updated on 2026-09-19

About this chapter

A mixture is homogeneous (uniform throughout — a solution) or heterogeneous (not uniform — sand in water, smoke, fog). Particle size decides which: below 1 nm it is a solution, 1 – 1000 nm a colloid, above 1000 nm a suspension. Concentration says how much solute is present. Three percentage forms are used: % m/m = (mass of solute ÷ mass of solution) × 100, % m/v = (mass of solute ÷ volume of solution) × 100, and % v/v = (volume of solute ÷ volume of solution) × 100. Solubility is the maximum mass of solute that dissolves in 100 g (or 100 mL) of solvent at a stated temperature. For most solids it rises with temperature; for gases in liquids it falls. Cooling a hot saturated solution therefore throws out the excess solute as crystals . Homogeneous mixtures are separated by crystallization (p

  • Chapter opener
  • .1 How Can We Classify Mixtures?
  • .2 Solutions; 5.2.1 Concentration of a solution
  • .2.2 How do we express concentration?
  • .2.3 Solubility of substances
  • .3.1 Crystallization
  • .3.2 Distillation
  • .3.3 Paper Chromatography
  • .4.1 Separation of two immiscible liquids
  • .4.2 Sublimation
Quick revision
TermWhat it meansKey number or ruleWhere it appears
Homogeneous mixture (solution)Same composition in every part; solute particles not visibleParticle size < 1 nmSugar in water, vinegar, soda, brass
Heterogeneous mixtureComposition differs from part to partTwo or more visible phasesSand in water, oil and water, smoke, fog
SuspensionInsoluble solid particles held up in a liquid; they settle on standingParticle size > 1000 nmMuddy water, chalk in water, tea leaves in water
ColloidParticles too small to settle, too large to be a solutionParticle size 1 – 1000 nmMilk, blood, ice cream, tomato sauce, smoke
Mass by mass percentageGrams of solute in 100 g of solution% m/m = (mass of solute ÷ mass of solution) × 100Milk powder, spice mixes, packaged food labels
Mass by volume percentageGrams of solute in 100 mL of solution% m/v = (mass of solute ÷ volume of solution) × 1005% glucose drip, 0.9% m/v saline drip
Volume by volume percentageMillilitres of solute in 100 mL of solution% v/v = (volume of solute ÷ volume of solution) × 100Vinegar (5% v/v acetic acid), perfumes
SolubilityMaximum mass of solute that dissolves in 100 g of solvent at a stated temperatureRises with temperature for most solids; falls for gasesSolubility curves, Fig. 5.6; Table 5.4
CrystallizationPure solid separates as crystals when a hot saturated solution is cooled slowlySlow cooling → larger, better-formed crystalsCopper sulfate crystals, salt from seawater
DistillationLiquid is boiled off, then condensed and collected separatelyWorks when boiling points differ by about 25 °C or moreAcetone (56 °C) and water (100 °C); Deg-Bhapka ittar
Fractional distillationSeparates components whose boiling points are closeBoiling point difference less than 25 °CCrude petroleum → LPG, petrol, kerosene, diesel
Sublimation / depositionSolid → vapour directly (below its melting point) / vapour → solid directlyNo liquid stage at any pointCamphor and sand, naphthalene, dry ice
CentrifugationRapid spinning; the centrifugal force drives heavier particles outwards and downUsed where filtration is too coarseBlood → plasma, platelets, WBC, RBC; the paperfuge
CoagulationA coagulant makes fine particles clump so that they settleAlum (fitkari) in muddy water; lemon juice in milkWater purification, making paneer
Tyndall effectScattering of light by dispersed particles makes the beam path visibleShown by colloids and suspensions, not by solutionsLaser through mixtures A, B, C; stadium floodlights
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Exercises

  1. Chapter opener — Think It Over Page 72
  2. .1 How Can We Classify Mixtures? — In-text Questions Page 735
  3. .1 How Can We Classify Mixtures? — Activity 5.1: Let us experiment — Group activity Page 735
  4. .2 Solutions; 5.2.1 Concentration of a solution — In-text Questions Page 745
  5. .2.2 How do we express concentration? — Pause and Ponder Page 765
  6. .2.3 Solubility of substances — Activity 5.2: Let us represent solubility graphically Page 775
  7. .2.3 Solubility of substances — In-text Questions Page 775
  8. .3.1 Crystallization — Activity 5.3: Let us prepare Page 785
  9. .3.1 Crystallization — Think as a Scientist Page 795
  10. .3.1 Crystallization — Pause and Ponder Page 795
  11. .3.1 Crystallization — Activity 5.4: Let us describe a process Page 795
  12. .3.1 Crystallization — Ready to Go Beyond Page 795
  13. .3.2 Distillation — In-text Questions Page 805
  14. .3.3 Paper Chromatography — Activity 5.5: Let us investigate Page 825
  15. .3.3 Paper Chromatography — In-text Questions Page 825
  16. .3.3 Paper Chromatography — Pause and Ponder Page 825
  17. .4.1 Separation of two immiscible liquids — Activity 5.6: Let us separate Page 835
  18. .4.1 Separation of two immiscible liquids — What if … Page 835
  19. .4.1 Separation of two immiscible liquids — In-text Questions Page 835
  20. .4.2 Sublimation — Activity 5.7: Let us explore Page 845
  21. .4.2 Sublimation — Pause and Ponder Page 845
  22. .4.2 Sublimation — In-text Questions Page 845
  23. .4.3 Suspensions — In-text Questions Page 855
  24. .4.3 A. Centrifugation — Threads of Curiosity Page 855
  25. The Paperfuge — Bridging Science and Society Page 86
  26. .4.3 A. Centrifugation — Activity 5.8: Let us make a model Page 865
  27. .4.3 B. Coagulation; 5.4.4 Colloids — In-text Questions Page 865
  28. Donate Blood — Bridging Science and Society Page 87
  29. .4.4 Colloids — In-text Questions Page 875
  30. .5 Tyndall Effect — In-text Questions Page 885
  31. .5 Tyndall Effect — Pause and Ponder Page 885
  32. .5 Tyndall Effect — Activity 5.9 Page 885
  33. Separation in nature and in daily life — In-text Questions Page 89
  34. End-of-chapter questions — Revise, Reflect, Refine Page 90 – 93
  35. Projects and investigations — The Journey Beyond Page 93
  36. An open question for you to carry forward — The Quest Continues … Page 93
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