New NCERT Exploration · Class 9 Science · Chapter 5: Exploring Mixtures and their Separation
This chapter explains what mixtures are and how they are classified into homogeneous and heterogeneous mixtures. It covers solutions, concentration and solubility, and the methods used to separate the parts of a mixture. It ends with suspensions, colloids and the Tyndall effect.
From the Class 9 Science Short Notes, made as per the new NCERT book Exploration · Pages 29–38 of the book.
Key points
- A mixture is formed by mixing two or more substances physically, without any chemical change; its parts keep their own properties.
- A homogeneous mixture has uniform composition throughout (e.g. sugar solution); a heterogeneous mixture does not (e.g. sand in water).
- A solution is a homogeneous mixture made of a solute dissolved in a solvent; its particles are smaller than 1 nm and do not scatter light.
- Solubility is the maximum amount of solute that dissolves in a fixed amount of solvent at a given temperature.
- Solubility of solids usually increases with temperature, while solubility of gases usually decreases.
- Crystallisation gives pure solid crystals from a saturated solution, like blue copper sulfate crystals on cooling.
- Distillation separates a liquid from a solution or two miscible liquids with different boiling points; fractional distillation is used when boiling points are close.
- Petroleum is separated into fractions like petrol, kerosene, diesel and bitumen in a fractionating tower.
- Paper chromatography separates the coloured components of inks or dyes.
- A separating funnel separates immiscible liquids like oil and water; sublimation separates substances like camphor.
- Centrifugation separates components by density through rapid spinning; alum causes coagulation of impurities in muddy water.
- Colloid particles are between 1 nm and 1000 nm, do not settle and scatter light (Tyndall effect).
Formulas
| Concentration of a solution | Concentration = Amount of solute ÷ Amount of solution Also written as amount of solute ÷ amount of solvent |
| Mass by mass percentage | (Mass of solute ÷ Mass of solution) × 100 |
| Mass by volume percentage | (Mass of solute ÷ Volume of solution) × 100 |
| Volume by volume percentage | (Volume of solute ÷ Volume of solution) × 100 |
| Solution | Solution = Solute + Solvent |
Key terms
- Mixture: A substance made by physically mixing two or more substances without chemical change.
- Solute: The substance that gets dissolved in a solvent.
- Solvent: The substance in which a solute gets dissolved.
- Solubility: Maximum amount of solute that dissolves in a fixed amount of solvent at a given temperature.
- Crystallisation: Getting pure solid crystals from a saturated solution.
- Sublimation: A solid changing directly into vapour on heating and back into solid on cooling.
- Suspension: A heterogeneous mixture of insoluble solid particles in a liquid that settle when left undisturbed.
- Colloid: A heterogeneous mixture whose particle size is between that of a solution and a suspension.
- Tyndall effect: Scattering of a light beam by tiny particles, which makes the beam's path visible.
Diagrams to learn
- Homogeneous and heterogeneous mixtures (sugar and sand in water)
- Crystallisation of copper sulfate
- Labelled distillation apparatus
- Fractional distillation of crude petroleum (fractionating tower)
- Paper chromatography experiment steps
- Separating funnel for oil and water
- Sublimation of camphor
- Centrifuge separating blood components
- Coagulation of muddy water with alum
- Table of types of colloids
- Particle size scale for solution, colloid and suspension
- Tyndall effect in a dark room
- Solutions do not show the Tyndall effect, but colloids and suspensions scatter light.
- In fractional distillation, fractions at the top have lower boiling points and are lighter; those at the bottom have higher boiling points and are heavier.
- In a separating funnel, oil is less dense and forms the upper layer, while water forms the lower layer.
A real page from the book
Get the full chapter in the book
This page is a summary. The Class 9 Science Short Notes has the complete chapter in colour, with every diagram and worked example.
Frequently asked questions
What is the difference between a homogeneous and a heterogeneous mixture?
A homogeneous mixture has the same composition and properties throughout, like a sugar or salt solution. A heterogeneous mixture has different composition in different parts, like sand in water.
What is the Tyndall effect?
When a beam of sunlight enters a dark room, tiny dust particles scatter the light and make its path visible. This is called the Tyndall effect and is a characteristic property of colloids.
How is petroleum separated into useful products?
Crude petroleum is heated and its vapours enter a fractionating tower. Different fractions condense at different levels because they have different boiling points, giving products like petrol, kerosene, diesel and bitumen.
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