CBSE Class 9 Science Revision Notes Chapter 5: Exploring Mixtures and Their Separation

Mixtures contain two or more substances that can often be separated using differences in size, density, solubility or boiling point. CBSE Class 9 Science Chapter 5 explains solutions, suspensions, colloids and the methods used to separate their components.

Mixtures are present in food, medicines, soil, seawater, blood and many industrial products. Some mixtures appear uniform throughout, while others contain visibly different components. Their properties help us decide how they can be separated.

These CBSE Class 9 Science Revision Notes Chapter 5 follow the current 2026–27 chapter. Use them to revise the classification of mixtures, concentration formulas, solubility, crystallization, distillation, chromatography, suspensions, colloids and the Tyndall effect.

Key Takeaways

• Homogeneous mixture: It has a uniform composition throughout.
• Concentration: It shows the amount of solute present in a solution.
• Separation method: It depends on particle size, density, solubility, physical state or boiling point.
• Tyndall effect: Colloids and suspensions scatter light, while transparent solutions do not.

Access Class 9 Science Chapter 5 Exploring Mixtures and Their Separation Notes in 30 Minutes

Revise the chapter in three parts:

First 10 minutes: Homogeneous and heterogeneous mixtures, solutions, concentration and solubility

Next 10 minutes: Crystallization, distillation, fractional distillation and paper chromatography

Final 10 minutes: Separating funnel, sublimation, centrifugation, coagulation, suspensions, colloids and Tyndall effect

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Classification of Mixtures

A mixture contains two or more substances combined physically. Its components usually retain their individual properties.

Mixtures can be classified as homogeneous or heterogeneous.

Homogeneous Mixtures

A homogeneous mixture has the same composition throughout.

Its components are distributed uniformly and cannot be distinguished easily. A homogeneous mixture is also called a solution.

Examples include:

• Sugar dissolved in water
• Salt solution
• Vinegar
• Aerated drinks
• Air
• Brass

A properly mixed sugar solution tastes equally sweet in every portion.

Heterogeneous Mixtures

A heterogeneous mixture has a non-uniform composition.

Its components may be visible, form separate layers or settle when the mixture is left undisturbed.

Examples include:

• Sand and water
• Oil and water
• Muddy water
• Smoke
• Milk
• Blood

Solutions, Solutes and Solvents

A solution is a homogeneous mixture of two or more substances.

The substance that dissolves is called the solute. The substance that dissolves the solute is called the solvent.

In a sugar solution:

• Sugar is the solute.
• Water is the solvent.
• Sugar solution is the mixture formed.

The correct proportion of solute and solvent is important. Medicines, pesticides and food products may not work properly if their concentration is incorrect.

Concentration of a Solution

The concentration of a solution is the amount of solute dissolved in a given amount of solvent or solution.

A solution with less solute is called dilute. A solution containing more solute is called concentrated.

Concentration can be expressed using percentage.

Mass by Mass Percentage

Mass by mass percentage shows the mass of solute present in 100 g of solution.

Mass by mass percentage = Mass of solute ÷ Mass of solution × 100

The total mass of the solution is:

Mass of solution = Mass of solute + Mass of solvent

Example:

10 g of salt is dissolved in 90 g of water.

Mass of solution = 10 g + 90 g = 100 g

Mass by mass percentage = 10 ÷ 100 × 100 = 10%

The solution contains 10% salt by mass.

Mass by Volume Percentage

Mass by volume percentage shows the mass of solute present in 100 mL of solution.

Mass by volume percentage = Mass of solute ÷ Volume of solution × 100

Example:

5 g of glucose is present in 100 mL of solution.

Mass by volume percentage = 5 ÷ 100 × 100 = 5%

The solution is a 5% m/v glucose solution.

A saline drip containing 0.9 g of sodium chloride in 100 mL of solution is written as 0.9% m/v.

Volume by Volume Percentage

Volume by volume percentage is used when both the solute and solvent are liquids.

It shows the volume of solute present in 100 mL of solution.

Volume by volume percentage = Volume of solute ÷ Volume of solution × 100

Example:

1 mL of pesticide is used to prepare 100 mL of spray.

Volume by volume percentage = 1 ÷ 100 × 100 = 1%

Solubility and Saturated Solutions

Solubility is the maximum amount of solute that dissolves in a fixed quantity of solvent at a given temperature.

A saturated solution cannot dissolve any more solute at that temperature.

An unsaturated solution can still dissolve more solute.

Effect of Temperature on Solubility

The solubility of most solid solutes in liquids increases with temperature.

Hot water can generally dissolve more solid solute than cold water. Therefore, a hot saturated solution may deposit crystals when it cools.

The solubility of gases in liquids usually decreases as temperature rises.

Temperature must always be mentioned while stating solubility.

Solubility Curve

A solubility curve is a graph showing how the solubility of a substance changes with temperature.

• The horizontal axis represents temperature.
• The vertical axis represents solubility.
• A rising curve shows an increase in solubility.
• Different substances have different solubility curves.

A steep curve shows that temperature has a strong effect on the solubility of that substance.

Separation of Homogeneous Mixtures

Homogeneous mixtures require methods based on properties such as solubility, boiling point and movement through a medium.

Crystallization

Crystallization is the process of forming pure solid crystals from a saturated solution.

It is used to:

• Obtain pure solids
• Remove dissolved impurities
• Separate soluble solids
• Produce well-shaped crystals

The method depends on changes in solubility with temperature.

Main steps of crystallization:

1. Prepare a hot saturated solution.
2. Filter it to remove insoluble impurities.
3. Allow the solution to cool slowly.
4. Collect the crystals.
5. Rinse them with cold water.
6. Dry the crystals.

Slow cooling produces larger and better-shaped crystals. Rapid cooling usually produces smaller crystals.

Copper sulfate, common salt and sugar can form crystals.

Evaporation and Crystallization

Evaporation removes a solvent and leaves the dissolved solid behind.

Crystallization is preferred when a purer solid is needed. It also reduces the risk of some substances decomposing during strong heating.

Distillation

Distillation separates a liquid from dissolved solids or separates two miscible liquids.

The mixture is heated until the liquid with the lower boiling point vaporises. The vapour then passes through a condenser.

The condenser cools the vapour and changes it back into liquid. The collected liquid is called the distillate.

Distillation is suitable when the boiling points of two liquids differ by about 25°C or more.

A mixture of acetone and water can be separated by this method.

• Acetone boils at about 56°C.
• Water boils at 100°C.

Acetone vaporises first and is collected after condensation.

Fractional Distillation

Fractional distillation separates miscible liquids whose boiling points differ by less than about 25°C.

It is commonly used in petroleum refineries.

Crude petroleum is separated into:

• Petroleum gas
• Petrol
• Kerosene
• Diesel
• Lubricating oil
• Bitumen

Each fraction has a different boiling range.

Paper Chromatography

Paper chromatography separates components according to differences in their movement through paper.

A solvent rises through the paper and carries the components with it. Different substances move at different rates.

Main steps:

1. Draw a pencil line near the bottom of the paper.
2. Place a small sample spot on the line.
3. Dip the lower end of the paper in the solvent.
4. Keep the sample spot above the solvent level.
5. Allow the solvent to rise.
6. Observe the separated spots.

Paper chromatography can separate:

• Colours in black ink
• Food colours
• Pigments in flowers
• Pigments in leaves

The sample spot must remain above the solvent level. Otherwise, it may dissolve directly into the liquid.

Separation of Heterogeneous Mixtures

Heterogeneous mixtures can be separated using differences in density, particle size, physical state or magnetic properties.

Separating Funnel

A separating funnel is used to separate two immiscible liquids.

Immiscible liquids do not mix and form separate layers.

For example, mustard oil and water form two layers:

• Mustard oil forms the upper layer.
• Water forms the lower layer.

The lower liquid is drained first through the stopcock. The upper layer is then collected separately.

This method works because the liquids have different densities.

Sublimation and Deposition

Sublimation is the direct change of a solid into vapour without passing through the liquid state.

Deposition is the direct change of vapour back into a solid.

A mixture of camphor and sand can be separated by sublimation.

• Camphor changes into vapour on heating.
• Sand remains in the dish.
• Camphor vapours cool and deposit on the funnel.

Naphthalene and dry ice also undergo sublimation.

Centrifugation

Centrifugation separates components by spinning a mixture at high speed.

The heavier particles move outward and settle. The lighter liquid remains above them.

Centrifugation is used to separate:

• Blood cells from plasma
• Cream from milk
• Fine suspended particles from liquids

A paperfuge is a hand-powered device that performs centrifugation without electricity.

Coagulation

Coagulation causes fine suspended particles to form larger clumps.

The substance added for this purpose is called a coagulant.

Powdered alum can be added to muddy water. It causes the fine particles to join and form larger clumps.

These clumps settle by sedimentation. They can then be removed by decantation or filtration.

Paneer formation also involves coagulation. Lemon juice or vinegar causes milk proteins to clump together.

Alloys as Homogeneous Mixtures

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Metals are heated, mixed and then allowed to cool.

Examples include:

• Brass: Copper and zinc
• Bronze: Copper and tin
• Stainless steel: Iron mixed with carbon, chromium, nickel and other elements

The components of an alloy cannot be separated by ordinary physical methods.

Alloys are usually stronger, harder or more resistant to corrosion than their components.

Solutions, Suspensions and Colloids

Solutions, suspensions and colloids differ mainly in particle size, visibility, settling and light scattering.

Solutions

A solution has particles smaller than 1 nm.

Its particles:

• Cannot be seen with the naked eye
• Do not settle
• Cannot be separated by ordinary filtration
• Do not scatter light in a transparent solution

Salt water is an example of a solution.

Suspensions

A suspension is a heterogeneous mixture containing large, insoluble particles.

Its particles are larger than 1000 nm.

Properties of a suspension:

• Particles are visible.
• Particles settle when left undisturbed.
• The mixture scatters light.
• Components can be separated by filtration.

Examples include sand in water, muddy water and chalk powder in water.

Colloids

A colloid has particles between 1 nm and 1000 nm.

Its particles are larger than those in a solution but smaller than those in a suspension.

Properties of a colloid:

• It is heterogeneous.
• Its particles are not visible to the naked eye.
• The particles remain dispersed.
• It scatters light.
• It cannot be separated by ordinary filtration.
• Its components may be separated by centrifugation.

Examples include milk, blood, smoke, fog and ice cream.

Tyndall Effect

The Tyndall effect is the scattering of light by particles in a colloid or suspension.

The path of a light beam becomes visible because the particles scatter it.

This effect can be observed:

• When sunlight passes through gaps between tree leaves
• In a dusty room
• In stadium floodlights
• In smoke
• In fog
• In diluted milk

A transparent solution does not show the Tyndall effect. Its particles are too small to scatter visible light significantly.

Dispersed Phase and Dispersion Medium

A colloid has two main components.

• Dispersed phase: The particles spread throughout the colloid
• Dispersion medium: The substance in which the particles are dispersed

In milk, fat droplets form the dispersed phase and water forms the dispersion medium.

Emulsions

An emulsion is a colloid in which one liquid is dispersed in another liquid.

Examples include:

• Milk
• Butter
• Cream
• Body lotion
• Cold cream

Milk is an oil-in-water emulsion. Butter is a water-in-oil emulsion.

Emulsifying agents help keep the liquids mixed. Proteins act as emulsifying agents in milk.

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