Complete Solutions and Summary of Is Matter Around Us Pure – NCERT Class 9, Science, Chapter 2 – Summary, Questions, Answers, Extra Questions
Detailed summary and explanation of Chapter 2 “Is Matter Around Us Pure” with all question answers, extra questions, and solutions from NCERT Class IX, Science.
Updated: 3 weeks ago
Categories: NCERT, Class IX, Science, Summary, Extra Questions, Is Matter Around Us Pure, Chapter 2
Tags: Is Matter Around Us Pure, Class 9 Science, NCERT, Chapter 2, Mixtures, Compounds, Elements, Pure Substances, Separation of Substances, Summary, Answers, Extra Questions
Is Matter Around Us Pure?
Chapter 2: Science
Complete Study Guide with Interactive Learning
Chapter Overview
2
Types of Mixtures
3
Types of Solutions
118
Known Elements
9
Types of Colloids
What You'll Learn
Pure Substances vs Mixtures
Understanding what makes a substance pure and how mixtures differ.
Types of Mixtures
Exploring homogeneous and heterogeneous mixtures, solutions, suspensions, colloids.
Separation Techniques
Methods to separate components of mixtures like evaporation, filtration, centrifugation.
Physical and Chemical Changes
Differentiating between physical changes and chemical reactions.
Historical Context
The chapter discusses the concept of pure substances and mixtures, with historical references to scientists like Robert Boyle who first used the term 'element' in 1661, and Antoine Lavoisier who defined elements in 1743-94. It explains how matter is classified into elements, compounds, and mixtures based on composition.
Key Highlights
Matter is classified as pure substances (elements, compounds) or mixtures (homogeneous like solutions, heterogeneous like suspensions and colloids). Solutions have concentration measures, colloids show Tyndall effect, and chemical changes form new substances unlike physical changes.
Comprehensive Chapter Summary
1. Introduction to Pure Matter and Mixtures
The chapter begins by questioning the purity of common items like milk, ghee, etc. Pure for scientists means single type of particles, while most matter is mixtures of pure substances like sea water, soil.
2. What is a Mixture?
Definition
Mixtures contain more than one pure substance, separated by physical processes like evaporation.
Types of Mixtures
Homogeneous (uniform composition, e.g., salt in water) and heterogeneous (non-uniform, e.g., salt and sulphur).
Examples
Solutions are homogeneous; suspensions and colloids are heterogeneous.
3. Solutions
Properties
Homogeneous, particles <1 nm, no Tyndall effect, stable, can't filter.
Concentration
Mass/mass %, mass/volume %, volume/volume %. Saturated when no more solute dissolves.
Solubility
Amount of solute in saturated solution at given temperature; varies with temperature.
4. Suspensions
Properties
Heterogeneous, particles visible, Tyndall effect, unstable, can filter.
5. Colloidal Solutions
Properties
Heterogeneous but appear homogeneous, particles 1-1000 nm, Tyndall effect, stable, centrifuge to separate.
Tyndall Effect
Scattering of light by colloidal particles, making beam visible.
6. Physical and Chemical Changes
Physical changes alter form without new substances; chemical changes form new substances via reactions.
7. Types of Pure Substances
Elements (can't break down, metals/non-metals/metalloids) and compounds (fixed proportion, different properties from elements).
Key Concepts and Definitions
Pure Substance
Consists of single type of particles, same chemical nature.
Mixture
More than one pure substance, variable composition.
Solution
Homogeneous mixture, solvent dissolves solute.
Saturated Solution
Maximum solute dissolved at given temperature.
Suspension
Heterogeneous, particles settle, visible.
Colloid
Heterogeneous, particles scatter light (Tyndall effect).
Important Facts and Figures
118
Elements Known
92
Naturally Occurring Elements
1 nm
Solution Particle Size
1-1000 nm
Colloid Particle Size
>1000 nm
Suspension Particle Size
Questions and Answers from Chapter
Short Questions
Q1. What is meant by a substance?
Answer: Pure single form of matter.
Q2. List the points of differences between homogeneous and heterogeneous mixtures.
Answer: Homogeneous: uniform; Heterogeneous: non-uniform.
Q3. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer: Homogeneous: salt water; Heterogeneous: oil water.
Q4. How are sol, solution and suspension different from each other?
Answer: Solution: homogeneous; Sol: colloid; Suspension: heterogeneous.
Q5. Classify the following as chemical or physical changes: cutting of trees.
Answer: Physical.
Q6. Classify the following as chemical or physical changes: melting of butter in a pan.
Answer: Physical.
Q7. Classify the following as chemical or physical changes: rusting of almirah.
Answer: Chemical.
Q8. Classify the following as chemical or physical changes: boiling of water to form steam.
Answer: Physical.
Q9. Classify the following as chemical or physical changes: passing of electric current through water and the water breaking down into hydrogen and oxygen gases.
Answer: Chemical.
Q10. Classify the following as chemical or physical changes: dissolving common salt in water.
Answer: Physical.
Q11. Classify the following as chemical or physical changes: making a fruit salad with raw fruits.
Answer: Physical.
Q12. Classify the following as chemical or physical changes: burning of paper and wood.
Answer: Chemical.
Q13. Try segregating the things around you as pure substances or mixtures.
Answer: Pure: gold; Mixture: air.
Q14. Which separation techniques will you apply for the separation of the following? Sodium chloride from its solution in water.
Answer: Evaporation.
Q15. Which separation techniques will you apply for the separation of the following? Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
Answer: Sublimation.
Medium Questions
Q1. Which separation techniques will you apply for the separation of the following? Small pieces of metal in the engine oil of a car.
Answer: Filtration or centrifugation. Particles settle or are separated by spinning. (3 marks)
Q2. Which separation techniques will you apply for the separation of the following? Different pigments from an extract of flower petals.
Answer: Chromatography. Separates based on solubility differences. (3 marks)
Q3. Which separation techniques will you apply for the separation of the following? Butter from curd.
Answer: Centrifugation. Separates denser particles. (3 marks)
Q4. Which separation techniques will you apply for the separation of the following? Oil from water.
Answer: Separating funnel. Immiscible liquids separate. (3 marks)
Q5. Which separation techniques will you apply for the separation of the following? Tea leaves from tea.
Answer: Filtration. Leaves retained on filter. (3 marks)
Q6. Which separation techniques will you apply for the separation of the following? Iron pins from sand.
Answer: Magnetic separation. Pins attracted to magnet. (3 marks)
Q7. Which separation techniques will you apply for the separation of the following? Wheat grains from husk.
Answer: Winnowing. Wind separates lighter husk. (3 marks)
Q8. Which separation techniques will you apply for the separation of the following? Fine mud particles suspended in water.
Answer: Centrifugation. Mud settles faster. (3 marks)
Q9. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer: Boil water (solvent), add tea (solute) to dissolve, strain to get filtrate, residue leaves. (3 marks)
Q10. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Answer: 26.47%. Mass % = (36/136) * 100. (3 marks)
Q11. What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
Answer: 31 g. From table, solubility 62 g/100 g, so (62/100)*50 = 31 g. (3 marks)
Q12. Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
Answer: Crystals form. Solubility decreases with temperature. (3 marks)
Q13. Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
Answer: KNO3:32, NaCl:36, KCl:35, NH4Cl:37. NH4Cl highest. (3 marks)
Q14. What is the effect of change of temperature on the solubility of a salt?
Answer: Increases with temperature for most salts. (3 marks)
Q15. Explain the following giving examples: Saturated solution.
Answer: No more solute dissolves, e.g., 36g NaCl in 100g water at 293K. (3 marks)
Long Questions
Q1. Explain the following giving examples: Pure substance.
Answer: Single type of particles, e.g., gold element, water compound. Pure substances have fixed composition and properties, unlike mixtures. Elements can't be broken down, compounds have fixed ratios.
Q2. Explain the following giving examples: Colloid.
Answer: Heterogeneous, particles scatter light, e.g., milk. Colloids have dispersed phase and medium, show Tyndall effect, stable, separated by centrifugation.
Q3. Explain the following giving examples: Suspension.
Answer: Heterogeneous, particles visible and settle, e.g., mud in water. Unstable, filterable, show Tyndall effect.
Q4. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air, soil, vinegar, filtered tea.
Answer: Homogeneous: soda water, air, vinegar, filtered tea. Heterogeneous: wood, soil. Explanation of uniform vs non-uniform composition.
Q5. How would you confirm that a colourless liquid given to you is pure water?
Answer: Check boiling point 100°C, freezing 0°C, no residue on evaporation, pH 7. Pure water has specific physical properties without impurities.
Q6. Which of the following materials fall in the category of a “pure substance”? Ice, Milk, Iron, Hydrochloric acid, Calcium oxide, Mercury, Brick, Wood, Air.
Answer: Pure: Ice, Iron, Hydrochloric acid, Calcium oxide, Mercury. Others are mixtures. Explanation: Pure have single composition.
Q7. Identify the solutions among the following mixtures: Soil, Sea water, Air, Coal, Soda water.
Answer: Solutions: Sea water, Air, Soda water. Others heterogeneous. Solutions are homogeneous mixtures.
Q8. Which of the following will show “Tyndall effect”? Salt solution, Milk, Copper sulphate solution, Starch solution.
Answer: Milk, Starch solution. Colloids show Tyndall. Solutions don't scatter light.
Q9. Classify the following into elements, compounds and mixtures: Sodium, Soil, Sugar solution, Silver, Calcium carbonate, Tin, Silicon, Coal, Air, Soap, Methane, Carbon dioxide, Blood.
Answer: Elements: Sodium, Silver, Tin, Silicon. Compounds: Calcium carbonate, Soap, Methane, Carbon dioxide. Mixtures: Soil, Sugar solution, Coal, Air, Blood. Detailed classification based on composition.
Q10. Which of the following are chemical changes? Growth of a plant, Rusting of iron, Mixing of iron filings and sand, Cooking of food, Digestion of food, Freezing of water, Burning of a candle.
Answer: Chemical: Growth, Rusting, Cooking, Digestion, Burning. Physical: Mixing, Freezing. Chemical form new substances.
Q11. Classify the following as chemical or physical changes: cutting of trees, melting of butter in a pan, rusting of almirah, boiling of water to form steam, passing of electric current through water and the water breaking down into hydrogen and oxygen gases, dissolving common salt in water, making a fruit salad with raw fruits, burning of paper and wood.
Answer: Physical: cutting, melting, boiling, dissolving, making salad. Chemical: rusting, passing current (electrolysis), burning. Explanation with reasons for each.
Q12. Try segregating the things around you as pure substances or mixtures.
Answer: Pure: distilled water, gold. Mixtures: air, soil, milk. Classify based on composition and properties.
Q13. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer: Homogeneous: uniform throughout, e.g., sugar in water. Heterogeneous: non-uniform, e.g., sand in water. Detailed differences in composition, visibility, separation.
Q14. How are sol, solution and suspension different from each other?
Answer: Solution: true, particles <1nm. Sol: colloid, 1-1000nm. Suspension: >1000nm, settle. Properties comparison.
Q15. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Answer: Concentration = (36 / (36+100)) * 100 = 26.47%. Step-by-step calculation and explanation.
Interactive Knowledge Quiz
Test your understanding of Is Matter Around Us Pure?
Quick Revision Notes
Pure Substance
- Single type
- Elements/Compounds
- Fixed composition
Mixtures
- Homogeneous
- Heterogeneous
- Variable
Solutions
- Saturated
- Concentration %
- No Tyndall
Colloids/Suspensions
- Tyndall effect
- Stable/Unstable
- Filter/Centrifuge
Exam Strategy Tips
- Learn separation methods
- Understand Tyndall
- Practice concentrations
- Classify changes
- Memorize definitions
Group Discussions
No forum posts available.
Easily Share with Your Tribe
