Exploring Mixtures and their Separation
NCERT Class 9 Science • Chapter 5
Quick Answer
This Class 9 chemistry chapter explains pure substances and mixtures, including homogeneous and heterogeneous mixtures, solutions, suspensions, and colloids. Students learn separation techniques such as filtration, evaporation, distillation, chromatography, and centrifugation, along with concentration of solutions and the Tyndall effect.
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Key Terms
- Mixture
- A substance made of two or more components that are physically combined and can be separated by physical methods, without fixed proportions.
- Homogeneous Mixture
- A mixture with uniform composition throughout in which the components are not distinguishable, such as salt dissolved in water.
- Heterogeneous Mixture
- A mixture with non-uniform composition in which the different components can be seen or distinguished, such as sand in water.
- Solution
- A homogeneous mixture of a solute dissolved in a solvent, with particles too small to be seen or to scatter light.
- Colloid
- A mixture in which particles are intermediate in size, evenly spread, and large enough to scatter light, showing the Tyndall effect.
- Distillation
- A separation method that uses differences in boiling points to separate a liquid from a mixture by evaporating and then condensing it.
- Tyndall Effect
- The scattering of a beam of light by the suspended particles in a colloid, which makes the path of the light visible.
Frequently Asked Questions
What is the difference between a pure substance and a mixture?▾
A pure substance has a fixed composition and consistent properties, such as a single element or compound. A mixture contains two or more substances combined physically in variable proportions and can be separated by physical means.
What is the difference between a homogeneous and heterogeneous mixture?▾
A homogeneous mixture has uniform composition throughout with indistinguishable components, like sugar in water. A heterogeneous mixture has visibly different parts, like a mixture of sand and iron filings.
How can a mixture of salt and water be separated?▾
A mixture of salt and water can be separated by evaporation, where heating drives off the water as vapour and leaves the salt behind. Distillation can also recover both the water and the salt.
What is a colloid and how does it differ from a solution?▾
A colloid has particles that are larger than in a solution but still evenly dispersed, large enough to scatter light and show the Tyndall effect. A true solution has much smaller particles that do not scatter light.
What separation method is used for liquids with different boiling points?▾
Distillation is used to separate liquids with different boiling points. The mixture is heated so the more volatile liquid evaporates first, and its vapour is then condensed and collected separately.
What is the Tyndall effect?▾
The Tyndall effect is the scattering of light by colloidal particles, making a beam of light visible as it passes through the colloid. It helps distinguish colloids from true solutions, which do not scatter light.
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