Elements Compounds and Mixtures Class 9 ICSE — Simplified
Elements, compounds and mixtures Class 9 ICSE Chemistry explains the difference between pure substances and mixtures, and how each kind of mixture is separated. This chapter of the Simplified book covers evaporation and distillation for solid-liquid mixtures, fractional distillation and the separating funnel for liquid-liquid mixtures, heating for liquid-gas mixtures, and diffusion, dissolution and preferential liquefaction for gas-gas mixtures. Each technique works on one physical property.
Download Elements Compounds and Mixtures Class 9 ICSE Chemistry Chapter 3 PDF
Download the Elements Compounds and Mixtures Class 9 ICSE Chemistry chapter PDF from the Simplified textbook to revise offline or print for practice. It is the full chapter as printed in the book — 14 pages, 4 sections, 19 questions.
What is inside Chapter 3
14 pages · 4 sections · 19 exercise questions
| Section | Title |
|---|---|
| 29 | Separation of solid-liquid mixtures (Homogeneous mixtures). |
| 30 | Separation of liquid-liquid mixtures |
| 31 | Separation of liquid-gas mixtures. |
| 32 | Separation of gas-gas mixtures. |
- IMPORTANT QUESTIONS: 19 questions
29 Separation of solid-liquid mixtures (Homogeneous mixtures).
Homogeneous solid-liquid mixtures have a solute dissolved evenly in a liquid. Two techniques separate them: evaporation and distillation. Evaporation converts a liquid into vapour at any temperature below its boiling point by supplying heat. Distillation performs evaporation and condensation together.
Evaporation suits a soluble, non-volatile solid. Only the solute is recovered; the liquid escapes as vapour. Salt from salt water and sugar from sugar water are examples. Distillation recovers both components. Salt and water, sugar and water, and distilled water from water all use it.
Take 20 g of sugar dissolved in 100 mL of water. To recover only the sugar, heat gently. Water escapes as vapour, and sugar crystals remain behind. To recover both, distil the solution. Water vapour condenses in the condenser and collects separately, while sugar stays in the flask.
A common mistake is choosing evaporation when the solvent must also be recovered. Evaporation loses the liquid. Only distillation returns both the solute and the solvent. This chapter is part of the broader Class 9 ICSE chemistry book, where each technique builds on the last.
30 Separation of liquid-liquid mixtures
Liquid-liquid mixtures come in two classes. Miscible liquids mix evenly and form a homogeneous mixture. Immiscible liquids do not mix and form a heterogeneous mixture. The separating technique depends on which class the mixture belongs to.
Miscible liquids are separated by fractional distillation. The technique uses the difference in boiling points. The liquid with the lower boiling point distils first. The liquid with the higher boiling point distils last. Petroleum, ethyl alcohol and water, and benzene and toluene are examples.
Immiscible liquids are separated with a separating funnel. The technique uses the difference in densities. The heavier liquid settles below, and the lighter liquid floats above. Carbon tetrachloride and water, and carbon disulphide and water are examples.
| Mixture type | Technique | Property used |
|---|---|---|
| Miscible (homogeneous) | Fractional distillation | Difference in boiling points |
| Immiscible (heterogeneous) | Separating funnel | Difference in densities |
Consider a mixture of ethyl alcohol and water. Ethyl alcohol boils near 78°C, and water boils near 100°C. On heating, the alcohol vapour distils first and is collected. Water, with the higher boiling point, distils later. Fractional distillation uses this boiling point gap.
31 Separation of liquid-gas mixtures.
The separation of a liquid-gas mixture rests on one principle. The solubility of a gas in a liquid decreases as temperature rises. Heating the liquid drives the dissolved gas out. The gas escapes, and the liquid remains.
The chapter gives three examples. Carbon dioxide dissolved in water, sulphur dioxide dissolved in water, and dissolved gases in water all separate this way.
Fill a beaker with water that holds dissolved air. Heat it from 20°C to 80°C. As the temperature rises, the solubility of each gas falls. Bubbles of gas leave the liquid. This is exactly how a liquid-gas mixture is separated.
Two true or false checks confirm the idea. The solubility of a gas in a liquid decreases with a rise in temperature — true. The solubility increases with a decrease in pressure — false. You can verify the placement of this chapter in the official syllabus on the CISCE website.
32 Separation of gas-gas mixtures.
Gas-gas mixtures separate by three methods. The first is diffusion. By Graham’s law, the rate of diffusion is inversely proportional to the square root of density. Lighter gases diffuse faster than heavier ones. The gases must not react during the process. Nitrogen and carbon dioxide, and hydrogen and carbon dioxide, separate this way.
\text{Rate of diffusion} \propto \frac{1}{\sqrt{\text{density}}}
Compare hydrogen and carbon dioxide. Hydrogen is far lighter than carbon dioxide. By Graham’s law, hydrogen diffuses faster. Since the two gases do not react, diffusion separates them cleanly. If the gases reacted, the method would fail.
The second method is dissolution in a suitable solvent. One component dissolves, and the other is left behind. Carbon dioxide passes through caustic potash solution and is absorbed, leaving nitrogen. Hydrogen chloride gas dissolves in water, leaving nitrogen.
The third method is preferential liquefaction. The mixture expands suddenly, and one component liquefies under high pressure. In a mixture of ammonia and carbon monoxide, ammonia liquefies and carbon monoxide is left behind.
One caution applies to diffusion. The gases must not react during the process. If they do, the separation fails. The next chapter on atomic structure and chemical bonding explains why gases behave as they do.
What to practise from Elements Compounds and Mixtures Class 9 ICSE
One exercise block closes this chapter: IMPORTANT QUESTIONS, with 19 questions. The questions test the whole chapter in several ways.
- Naming the technique only for fifteen mixtures — magnet, evaporation, fractional distillation, separating funnel, sublimation, chromatography, and dissolving in a solvent.
- Naming elements by property — mercury as a liquid metal, graphite as a lustrous non-metal, and atomicity.
- Defining terms — element, compound, pure substance, residue, filtrate, distillate, sublimation, distillation, adsorption, sedimentation.
- Stating observations — heating iodine and ammonium chloride, and passing a magnet over iron and sulphur.
- Differentiating — metals from non-metals, and compounds from mixtures.
- Classifying solutions — tincture of iodine, milk, jellies, chalk water, soap lather, and sugar solution as true solution, colloidal solution, or suspension.
- Separating liquids — the process for miscible liquids and the apparatus for immiscible liquids.
An exam pattern note: the exercise asks for the technique name only. That is the fastest way to test recall of the whole chapter. If you can name the technique for each mixture, you have mastered the separation methods.
Elements Compounds and Mixtures Class 9 ICSE frequently asked questions
What are elements, compounds and mixtures in Class 9 ICSE?
An element is a pure substance made of atoms of only one kind. A compound is a pure substance where two or more elements combine chemically in fixed proportion by weight. A mixture is a physical combination of two or more substances in any proportion.
Which technique separates two miscible liquids in Class 9 ICSE?
Fractional distillation. It uses the difference in boiling points. The liquid with the lower boiling point distils first.
How do you separate a mixture of salt and water in Class 9 ICSE Chemistry?
Use evaporation or distillation. Evaporation recovers only the salt. Distillation recovers both the salt and the water.
Why does gas solubility in a liquid drop on heating in Class 9 ICSE Chemistry?
The solubility of a gas in a liquid decreases as temperature rises. Heating drives the dissolved gas out of the liquid. This is the principle behind separating liquid-gas mixtures.
How is a mixture of carbon dioxide and nitrogen separated in this ICSE chapter?
Pass the mixture through caustic potash solution. Carbon dioxide is absorbed, and nitrogen is left behind. This is dissolution in a suitable solvent.
Reference: ICSE Class 9 Chemistry textbook material, chapter 3: Elements, Compounds and Mixtures — CISCE-aligned.