Welcome to our comprehensive guide on Class 9 Science Chapter 2: Is Matter Around Us Pure?! If you’re a Class 9 student gearing up for exams or someone helping a student excel in Science, you’re in the right place. This blog post covers all the key questions and answers from the NCERT textbook for Chapter 2, breaking down complex concepts into simple, easy-to-understand explanations. By the end, you’ll master the ideas of pure substances, mixtures, and separation techniques—crucial for scoring high in your 2025 CBSE Science exams!
Chapter 2 builds on the foundation laid in Chapter 1 by exploring whether the matter around us is pure or a mix of different substances. From the air we breathe to the water we drink, this chapter helps you understand purity in scientific terms. Let’s dive into the Class 9 Science Chapter 2 questions and answers from the NCERT book, covering in-text and exercise questions.
Why Study Class 9 Science Chapter 2?
Before we get to the Q&As, let’s see why this chapter is important. In daily life, we encounter mixtures like tea, soil, and air, but how do we define purity? Chapter 2 explains the difference between pure substances (like gold or water) and mixtures (like lemonade or blood). It also introduces practical separation techniques—skills that are not only vital for exams but also connect to real-world applications like water purification. With about 20-25 marks allocated to Chemistry in the Class 9 Science syllabus, mastering this chapter can boost your overall score.
Let’s explore the chapter through its key questions and answers.
In-Text Questions and Answers: Page 15
Question 1: What is meant by a substance?
Answer:
A substance is a form of matter that has a definite composition and distinct properties. It can be either a pure element (like oxygen or iron) or a compound (like water or carbon dioxide). For example, sugar is a substance because it’s a compound (sucrose) with a fixed chemical makeup, unlike a mixture like juice, which varies in composition.
This question introduces the idea of purity, a central theme of the chapter.
Question 2: List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
| Property | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Composition | Uniform throughout | Non-uniform, varies in different parts |
| Appearance | Single phase, looks the same | Multiple phases, visibly different |
| Separation | Cannot be separated by simple means | Can be separated by physical methods |
| Examples | Saltwater, air | Sand and water, oil and water |
- Homogeneous mixtures have a consistent composition—like sugar dissolved in water.
- Heterogeneous mixtures show visible differences—like a salad or muddy water.
This distinction is key to understanding mixtures in this chapter.
In-Text Questions and Answers: Page 18
Question 1: Differentiate between an element and a compound.
Answer:
| Property | Element | Compound |
|---|---|---|
| Definition | A pure substance made of one type of atom | A pure substance made of two or more elements chemically combined |
| Composition | Cannot be broken down further | Can be broken into elements by chemical means |
| Examples | Oxygen (O₂), Iron (Fe) | Water (H₂O), Carbon dioxide (CO₂) |
| Bonding | No chemical bonding between atoms | Chemically bonded in a fixed ratio |
- An element is the simplest form of matter (e.g., gold).
- A compound is formed when elements combine chemically (e.g., salt—NaCl).
This question clarifies the building blocks of matter.
Question 2: How are sol, solution, and suspension different from each other?
Answer:
| Property | Solution | Sol | Suspension |
|---|---|---|---|
| Particle Size | Very small (< 1 nm) | Small (1-1000 nm) | Large (> 1000 nm) |
| Appearance | Clear, transparent | Cloudy but stable | Cloudy, particles settle |
| Stability | Stable, doesn’t settle | Stable, doesn’t settle | Unstable, settles over time |
| Examples | Sugar in water | Milk, blood | Muddy water, chalk in water |
- Solution: Homogeneous, tiny particles (e.g., saltwater).
- Sol: Colloidal, medium-sized particles (e.g., paint).
- Suspension: Heterogeneous, large particles that settle (e.g., sand in water).
This helps you identify different types of mixtures based on particle size and behavior.
In-Text Questions and Answers: Page 24
Question 1: 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 (mass by mass %) = (Mass of solute / Mass of solution) × 100
- Mass of solute (NaCl) = 36 g
- Mass of solvent (water) = 100 g
- Mass of solution = 36 g + 100 g = 136 g
Concentration = (36 / 136) × 100 = 26.47%
This numerical tests your understanding of solutions and concentration—a common exam question.
Question 2: How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?
Answer:
Kerosene and petrol can be separated by distillation. Since their boiling points differ by more than 25°C (petrol boils around 40-120°C, kerosene around 150-275°C), heat the mixture in a distillation flask. Petrol vaporizes first, rises, and condenses in a condenser, collecting separately. Kerosene, with a higher boiling point, remains in the flask. This method works because they’re miscible liquids with distinct boiling points.
Exercise Questions and Answers: Page 28
Question 1: Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride
(c) Small pieces of metal in the engine oil of a car
(d) Different pigments from an extract of flower petals
(e) Butter from curd
Answer:
(a) Evaporation: Heat the solution to evaporate water, leaving sodium chloride behind.
(b) Sublimation: Heat the mixture; ammonium chloride sublimes (turns to gas) and can be collected, leaving sodium chloride.
(c) Filtration: Filter the oil to trap metal pieces, letting oil pass through.
(d) Chromatography: Use paper chromatography to separate pigments based on their solubility and movement.
(e) Centrifugation: Spin the curd in a centrifuge; butter separates due to density differences.
Question 2: Write the steps you would use for making tea. Use the words: solution, solvent, solute, dissolve, soluble, insoluble, filtrate, and residue.
Answer:
To make tea:
- Boil water (the solvent) in a pot.
- Add tea leaves (the solute) to the water; some components dissolve to form a solution.
- Add sugar, which is soluble in water, and stir until it dissolves completely.
- Filter the mixture using a strainer; the liquid tea is the filtrate, while tea leaves are the residue (insoluble part).
- Serve the tea, a homogeneous solution of dissolved substances.
Question 3: Pragya tested the solubility of three different substances at different temperatures and collected the following data:
| Substance Dissolved | Temperature (K) | Solubility (g/100 g water) |
|---|---|---|
| Potassium nitrate | 293 | 32 |
| 313 | 62 | |
| Sodium chloride | 293 | 36 |
| 313 | 36 | |
| Potassium chloride | 293 | 35 |
| 313 | 40 |
(a) What mass of potassium nitrate would be needed to produce a saturated solution in 50 g of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride at 313 K in 100 g water. What is the concentration?
(c) At what temperature does sodium chloride’s solubility remain the same?
Answer:
(a) Solubility of potassium nitrate at 313 K = 62 g/100 g water.
For 50 g water: (62 / 100) × 50 = 31 g.
(b) Solubility of potassium chloride at 313 K = 40 g/100 g water.
Mass of solution = 100 g (water) + 40 g (solute) = 140 g.
Concentration = (40 / 140) × 100 = 28.57%.
(c) Sodium chloride’s solubility is 36 g at both 293 K and 313 K, so it remains the same across these temperatures.
Tips to Excel in Chapter 2
- Learn Definitions: Memorize terms like element, compound, mixture, and colloid.
- Practice Separation Techniques: Understand when to use filtration, distillation, etc.
- Solve Numericals: Focus on concentration and solubility problems.
- Use Diagrams: Sketch chromatography or distillation setups for clarity.
Class 9 Science Chapter 2: Is Matter Around Us Pure? teaches you to analyze the matter around you scientifically. From separating mixtures to calculating concentrations, these concepts are foundational for Chemistry and practical life. Use these questions and answers to prepare thoroughly for your 2025 exams and build a strong base for future studies.
For more resources, explore NCERT solutions and sample papers online. Drop your doubts in the comments—we’re here to help! Happy learning!
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