- A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition.
- Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases.
- A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount.
- Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator.
- Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature.
- A saturated solution contains the maximum dissolved solute under stated conditions.
- A suspension contains dispersed particles large enough to settle under gravity in many cases.
- Colloids have dispersed particles that do not settle rapidly under ordinary conditions.
- Colloidal particles may scatter a beam of light, making its path visible.
- Let heavier particles settle, then pour off the liquid carefully.
- A porous filter traps sufficiently large insoluble particles while allowing liquid through.
- Evaporation removes volatile solvent; crystallisation can recover a dissolved solid as crystals.
Use these notes alongside your current textbook. Check important formulas, worked answers and syllabus coverage with your teacher or official learning material.
Exploring Mixtures and their Separation — Class 9 Science, Exploration (2026–27)
Chapter 5. This original study guide explains core concepts with examples and worked practice. It is not a page-by-page verified transcription of NCERT activities, diagrams or numbered exercises. Refer to the prescribed textbook for exact official question wording.
Learning outcomes
Explain the concepts accurately, solve numerical or reasoning problems, choose suitable methods, and verify answers with correct units and assumptions.
Pure substances and mixtures
A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition.
Example and interpretation
Air is a mixture of gases, while distilled water is a compound.
Homogeneous and heterogeneous mixtures
Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases.
Example and interpretation
Salt solution is homogeneous; sand in water is heterogeneous.
Solute and solvent
A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount.
Example and interpretation
In dilute sugar water, sugar is solute and water is solvent.
Concentration
Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator.
Example and interpretation
10 g salt plus 90 g water gives 10% by mass.
Solubility and temperature
Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature.
Example and interpretation
Many solids dissolve more in hot water, but this is not universal.
Saturated solutions
A saturated solution contains the maximum dissolved solute under stated conditions.
Example and interpretation
Additional sugar remains undissolved once a solution is saturated.
Suspensions
A suspension contains dispersed particles large enough to settle under gravity in many cases.
Example and interpretation
Mud in water can settle on standing.
Colloids
Colloids have dispersed particles that do not settle rapidly under ordinary conditions.
Example and interpretation
Milk is a colloidal dispersion.
Tyndall effect
Colloidal particles may scatter a beam of light, making its path visible.
Example and interpretation
A beam is visible through fog because droplets scatter light.
Sedimentation and decantation
Let heavier particles settle, then pour off the liquid carefully.
Example and interpretation
Sand settles from water; water can be decanted.
Filtration
A porous filter traps sufficiently large insoluble particles while allowing liquid through.
Example and interpretation
Filter paper can separate chalk powder from water.
Evaporation and crystallisation
Evaporation removes volatile solvent; crystallisation can recover a dissolved solid as crystals.
Example and interpretation
Salt may be recovered from saline water by evaporation.
Distillation
Distillation uses vaporisation and condensation to separate components with different volatilities.
Example and interpretation
Simple distillation can recover water from salt solution.
Separating funnel
Immiscible liquids with different densities can be separated by allowing layers to form and draining one.
Example and interpretation
Oil and water can form separate layers.
Magnetic separation
A magnet can remove magnetic material from a nonmagnetic mixture.
Example and interpretation
Separate iron filings from sand using a magnet.
Sublimation
Certain solids pass directly into gas under suitable conditions, enabling separation.
Example and interpretation
Ammonium chloride can sublime under suitable controlled laboratory conditions.
Chromatography
Components move differently with mobile and stationary phases, causing separation.
Example and interpretation
Ink pigments may separate on paper chromatography.
Choosing a method
Choose based on particle size, solubility, magnetism, density, volatility and miscibility.
Example and interpretation
Use filtration for sand and water, but evaporation for dissolved salt.
Safety and limits
Heating, solvents and glassware require supervision; a single method may not achieve perfect purity.
Example and interpretation
Do not heat unknown mixtures or inhale vapours.
Chapter summary table
| Topic | Essential explanation | Example |
|---|---|---|
| Pure substances and mixtures | A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition. | Air is a mixture of gases, while distilled water is a compound. |
| Homogeneous and heterogeneous mixtures | Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases. | Salt solution is homogeneous; sand in water is heterogeneous. |
| Solute and solvent | A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount. | In dilute sugar water, sugar is solute and water is solvent. |
| Concentration | Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator. | 10 g salt plus 90 g water gives 10% by mass. |
| Solubility and temperature | Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature. | Many solids dissolve more in hot water, but this is not universal. |
| Saturated solutions | A saturated solution contains the maximum dissolved solute under stated conditions. | Additional sugar remains undissolved once a solution is saturated. |
| Suspensions | A suspension contains dispersed particles large enough to settle under gravity in many cases. | Mud in water can settle on standing. |
| Colloids | Colloids have dispersed particles that do not settle rapidly under ordinary conditions. | Milk is a colloidal dispersion. |
| Tyndall effect | Colloidal particles may scatter a beam of light, making its path visible. | A beam is visible through fog because droplets scatter light. |
| Sedimentation and decantation | Let heavier particles settle, then pour off the liquid carefully. | Sand settles from water; water can be decanted. |
| Filtration | A porous filter traps sufficiently large insoluble particles while allowing liquid through. | Filter paper can separate chalk powder from water. |
| Evaporation and crystallisation | Evaporation removes volatile solvent; crystallisation can recover a dissolved solid as crystals. | Salt may be recovered from saline water by evaporation. |
| Distillation | Distillation uses vaporisation and condensation to separate components with different volatilities. | Simple distillation can recover water from salt solution. |
| Separating funnel | Immiscible liquids with different densities can be separated by allowing layers to form and draining one. | Oil and water can form separate layers. |
| Magnetic separation | A magnet can remove magnetic material from a nonmagnetic mixture. | Separate iron filings from sand using a magnet. |
| Sublimation | Certain solids pass directly into gas under suitable conditions, enabling separation. | Ammonium chloride can sublime under suitable controlled laboratory conditions. |
| Chromatography | Components move differently with mobile and stationary phases, causing separation. | Ink pigments may separate on paper chromatography. |
| Choosing a method | Choose based on particle size, solubility, magnetism, density, volatility and miscibility. | Use filtration for sand and water, but evaporation for dissolved salt. |
| Safety and limits | Heating, solvents and glassware require supervision; a single method may not achieve perfect purity. | Do not heat unknown mixtures or inhale vapours. |
Original practice exercise 1 — Solved applications
- Question: A mixture contains 12 g sugar and 108 g water. Find mass percentage.
Solution: Total mass=120 g; sugar percentage=(12/120)×100=10%.
- Question: How would you separate iron filings, sand and salt?
Solution: First remove iron using a magnet. Dissolve the remaining mixture in water, filter out sand, then evaporate the filtrate to recover salt.
- Question: Why does filtration not remove dissolved salt from water?
Solution: Dissolved ions are much smaller than the pores of ordinary filter paper and pass through with the water.
- Question: How can water be recovered from salt water?
Solution: Use distillation: heat to vaporise water and cool the vapour to condense it; salt remains in the flask.
- Question: A student says milk is a true solution. Is this correct?
Solution: No. Milk is a colloidal dispersion containing fat droplets and other components, not a true molecular solution.
- Question: Which method is suitable for separating oil from water?
Solution: Allow the immiscible liquids to form layers and use a separating funnel, taking care with the interface.
- Question: Why can two inks travel different distances on chromatography paper?
Solution: Their components differ in affinity for the mobile solvent and stationary paper.
- Question: What is the difference between a saturated and unsaturated solution?
Solution: A saturated solution cannot dissolve additional solute under the stated conditions; an unsaturated one can.
- Question: Why is the Tyndall effect not a universal test for every mixture?
Solution: Scattering depends on particle size, concentration and optical properties; not all mixtures show an easily visible beam.
- Question: A 200 g solution contains 30 g salt. Calculate its mass percentage.
Solution: (30/200)×100=15% salt by mass.
Original practice exercise 2 — Concept questions with answers
- Question: Explain pure substances and mixtures.
Answer: A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition.
- Question: Explain homogeneous and heterogeneous mixtures.
Answer: Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases.
- Question: Explain solute and solvent.
Answer: A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount.
- Question: Explain concentration.
Answer: Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator.
- Question: Explain solubility and temperature.
Answer: Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature.
- Question: Explain saturated solutions.
Answer: A saturated solution contains the maximum dissolved solute under stated conditions.
- Question: Explain suspensions.
Answer: A suspension contains dispersed particles large enough to settle under gravity in many cases.
- Question: Explain colloids.
Answer: Colloids have dispersed particles that do not settle rapidly under ordinary conditions.
- Question: Explain tyndall effect.
Answer: Colloidal particles may scatter a beam of light, making its path visible.
- Question: Explain sedimentation and decantation.
Answer: Let heavier particles settle, then pour off the liquid carefully.
- Question: Explain filtration.
Answer: A porous filter traps sufficiently large insoluble particles while allowing liquid through.
- Question: Explain evaporation and crystallisation.
Answer: Evaporation removes volatile solvent; crystallisation can recover a dissolved solid as crystals.
Original practice exercise 3 — Higher-order reasoning
- Identify an everyday situation that demonstrates two different chapter concepts. Explain how they apply.
- Compare two methods, models or quantities introduced in the chapter and identify their limitations.
- Design a safe observation or calculation that tests one claim, listing variables and assumptions.
- Construct a multistep numerical or classification problem and verify its answer.
- Identify a common misconception and correct it using the chapter principles.
Frequently asked questions
A mixture contains 12 g sugar and 108 g water. Find mass percentage.
Total mass=120 g; sugar percentage=(12/120)×100=10%.
How would you separate iron filings, sand and salt?
First remove iron using a magnet. Dissolve the remaining mixture in water, filter out sand, then evaporate the filtrate to recover salt.
Why does filtration not remove dissolved salt from water?
Dissolved ions are much smaller than the pores of ordinary filter paper and pass through with the water.
How can water be recovered from salt water?
Use distillation: heat to vaporise water and cool the vapour to condense it; salt remains in the flask.
A student says milk is a true solution. Is this correct?
No. Milk is a colloidal dispersion containing fat droplets and other components, not a true molecular solution.
Which method is suitable for separating oil from water?
Allow the immiscible liquids to form layers and use a separating funnel, taking care with the interface.
Why can two inks travel different distances on chromatography paper?
Their components differ in affinity for the mobile solvent and stationary paper.
What is the difference between a saturated and unsaturated solution?
A saturated solution cannot dissolve additional solute under the stated conditions; an unsaturated one can.
Why is the Tyndall effect not a universal test for every mixture?
Scattering depends on particle size, concentration and optical properties; not all mixtures show an easily visible beam.
A 200 g solution contains 30 g salt. Calculate its mass percentage.
(30/200)×100=15% salt by mass.
Explain pure substances and mixtures.
A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition.
Explain homogeneous and heterogeneous mixtures.
Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases.
Explain solute and solvent.
A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount.
Explain concentration.
Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator.
Explain solubility and temperature.
Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature.
Revision checklist
- Explain and apply pure substances and mixtures.
- Explain and apply homogeneous and heterogeneous mixtures.
- Explain and apply solute and solvent.
- Explain and apply concentration.
- Explain and apply solubility and temperature.
- Explain and apply saturated solutions.
- Explain and apply suspensions.
- Explain and apply colloids.
- Explain and apply tyndall effect.
- Explain and apply sedimentation and decantation.
- Explain and apply filtration.
- Explain and apply evaporation and crystallisation.
- Explain and apply distillation.
- Explain and apply separating funnel.
- Explain and apply magnetic separation.
- Explain and apply sublimation.
- Explain and apply chromatography.
- Explain and apply choosing a method.
- Explain and apply safety and limits.
Official textbook
NCERT ePathshala: Exploration. The practice exercises here are original and are not claimed to be the complete official NCERT exercise answer key.
Frequently asked questions
A mixture contains 12 g sugar and 108 g water. Find mass percentage.
Total mass=120 g; sugar percentage=(12/120)×100=10%.
A 200 g solution contains 30 g salt. Calculate its mass percentage.
(30/200)×100=15% salt by mass.
Explain pure substances and mixtures.
A pure substance has a fixed chemical composition; a mixture combines substances without a fixed composition.
Explain homogeneous and heterogeneous mixtures.
Homogeneous mixtures appear uniform throughout; heterogeneous mixtures contain distinguishable regions or phases.
Explain solute and solvent.
A solute dissolves in a solvent to form a solution; the solvent is usually the component in greater amount.
Explain concentration.
Mass percent=(mass of solute/mass of solution)×100%. Always include both masses in the denominator.
Explain solubility and temperature.
Solubility is the maximum quantity that dissolves under specified conditions; it depends on solute, solvent and temperature.
