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9-10th Class

Is matter around us pure in easy notes

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Is Matter Around Us Pure? Class 9 Chemistry Notes, Summary, MCQs & Important Questions

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Complete Class 9 Chemistry chapter “Is Matter Around Us Pure?” notes, summary, MCQs, questions, and exam tips in simple language.

Introduction of the Chapter

The chapter Is Matter Around Us Pure? from Class 9 Chemistry explains whether the substances we see around us are truly pure or not. In daily life, we use milk, air, water, salt, sugar, and soft drinks. These substances may look pure but are often mixtures.

In science, a pure substance contains only one kind of particles. However, many materials around us are mixtures of two or more substances. This chapter helps students understand the difference between pure substances and mixtures, types of mixtures, methods of separation, and the concept of solutions.

Understanding Is Matter Around Us Pure? is essential for exams, practical applications, and higher-level chemistry learning.

Short Notes

  • Pure substances contain only one type of particles.
  • Elements and compounds are pure substances.
  • Mixtures contain two or more substances physically combined.
  • Mixtures can be homogeneous or heterogeneous.
  • Solutions are homogeneous mixtures.
  • Colloids appear uniform but scatter light.
  • Suspensions are heterogeneous mixtures with visible particles.
  • Tyndall effect is the scattering of light by colloidal particles.
  • Methods like filtration, evaporation, distillation, and chromatography separate mixtures.
  • Physical changes do not form new substances; chemical changes do.

Detailed Summary

The chapter Is Matter Around Us Pure? helps students understand the nature of substances and their composition. Everything around us is made of matter, but not all matter is pure.

Pure Substances

A pure substance consists of only one type of particles and has fixed properties. It cannot be separated into other substances by physical methods.

Pure substances are classified into:

1. Elements

Elements consist of only one kind of atom. They cannot be broken down into simpler substances by chemical methods.

Examples:

  • Iron
  • Oxygen
  • Copper
  • Gold

Elements are classified as:

  • Metals (iron, copper)
  • Non-metals (oxygen, sulfur)
  • Metalloids (silicon)

2. Compounds

Compounds are formed when two or more elements chemically combine in a fixed ratio.

Examples:

  • Water (H₂O)
  • Carbon dioxide (CO₂)
  • Sodium chloride (NaCl)

Properties of compounds differ from their constituent elements. For example, sodium is reactive and chlorine is poisonous, but sodium chloride is safe to eat.

Mixtures

A mixture contains two or more substances physically combined. Each component retains its properties.

Examples:

  • Air
  • Salt solution
  • Soil

Mixtures can be separated by physical methods.

Types of mixtures:

1. Homogeneous Mixtures

These mixtures have uniform composition throughout.

Examples:

  • Salt in water
  • Sugar solution
  • Air

They are also called solutions.

2. Heterogeneous Mixtures

These mixtures have non-uniform composition.

Examples:

  • Sand and water
  • Oil and water
  • Soil

Types of Solutions

A solution is a homogeneous mixture of solute and solvent.

  • Solute: substance that dissolves
  • Solvent: substance that dissolves the solute

Example: salt (solute) + water (solvent)

Solutions can exist in different states:

SoluteSolventExample
SolidLiquidSalt in water
LiquidLiquidAlcohol in water
GasGasAir

Concentration of a Solution

Concentration tells how much solute is present in a solution.

  • Dilute solution → small amount of solute
  • Concentrated solution → large amount of solute
  • Saturated solution → no more solute can dissolve
  • Unsaturated solution → more solute can dissolve

Colloids

Colloids are mixtures that appear homogeneous but are actually heterogeneous.

Examples:

  • Milk
  • Fog
  • Smoke

Properties:

  • Scatter light (Tyndall effect)
  • Particles do not settle down
  • Cannot be separated by filtration

Suspensions

Suspensions are heterogeneous mixtures with visible particles.

Examples:

  • Muddy water
  • Chalk powder in water

Properties:

  • Partiles are large
  • Settle down on standing
  • Can be filtered

Tyndall Effect

The scattering of light by colloidal particles is called the Tyndall effect.

Examples:

  • Sunlight through fog
  • Light passing through dusty air

Separation Techniques

Methods used to separate mixtures include:

Filtration – separates insoluble solids from liquids
Evaporation – separates dissolved solids from liquids
Distillation – separates components based on boiling points
Chromatography – separates dyes and pigments
Centrifugation – separates cream from milk

These methods are widely used in laboratories and industries.

Physical and Chemical Changes

Physical change

  • No new substance formed
  • Reversible Example: melting ice

Chemical change

  • New substance formed
  • Irreversible Example: rusting of iron

Flowchart / Mind Map

Matter
→ Pure Substances
  → Elements
  → Compounds

→ Mixtures
  → Homogeneous (Solutions)
  → Heterogeneous
    → Colloids
    → Suspensions

→ Separation Methods
  → Filtration
  → Distillation
  → Evaporation
  → Chromatography

Important Keywords with Meanings

  • Pure Substance – material with only one type of particles
  • Mixture – combination of substances physically mixed
  • Element – simplest form of matter
  • Compound – chemical combination of elements
  • Solution – homogeneous mixture
  • Solute – substance dissolved
  • Solvent – substance that dissolves solute
  • Colloid – mixture with intermediate particle size
  • Suspension – mixture with large visible particles
  • Tyndall Effect – scattering of light
  • Saturated Solution – no more solute dissolves

Important Questions & Answers

Very Short Questions (2–3 marks)

Short Questions (5 marks)

  1. Differentiate between pure substances and mixtures.
    Answer:
    Pure substances have fixed composition and cannot be separated physically. Mixtures have variable composition and can be separated by physical methods.
  2. Explain homogeneous and heterogeneous mixtures.
    Answer:
    Homogeneous mixtures have uniform composition (salt solution). Heterogeneous mixtures have non-uniform composition (sand in water).
  3. Describe properties of colloids.
    Answer:
    Colloids scatter light, do not settle, and cannot be filtered.
  4. Explain separation methods of mixtures.
    Answer:
    Filtration separates insoluble solids; evaporation removes solvent; distillation separates liquids; chromatography separates dyes.
  5. What is a solution? Explain its types.
    Answer:
    A solution is a homogeneous mixture. Types include solid-liquid, liquid-liquid, and gas-gas solutions.
  6. Define suspension and give properties.
    Answer:
    Suspension is a heterogeneous mixture with visible particles that settle down.
  7. Explain Tyndall effect with examples.
    Answer:
    Light scattering by colloids like fog and smoke.
  8. Distinguish between compounds and mixtures.
    Answer:
    Compounds are chemically combined; mixtures are physically mixed.
  9. What is concentration of a solution?
    Answer:
    Amount of solute present in a given amount of solution.
  10. Explain physical vs chemical changes.
    Answer:
    Physical changes do not form new substances; chemical changes form new substances.

30 MCQs with Answers

  1. A pure substance contains:
    A. Two elements
    B. One type of particles ✔
    C. Dust
    D. Air
  2. Salt dissolved in water is a:
    A. Suspension
    B. Solution ✔
    C. Colloid
    D. Compound
  3. Milk is a:
    A. Solution
    B. Colloid ✔
    C. Suspension
    D. Element
  4. Which shows Tyndall effect?
    A. Sugar solution
    B. Milk ✔
    C. Salt
    D. Water
  5. Which is a compound?
    A. Air
    B. Soil
    C. Water ✔
    D. Milk
  6. Muddy water is a:
    A. Solution
    B. Colloid
    C. Suspension ✔
    D. Element
  7. Solvent in salt solution is:
    A. Salt
    B. Water ✔
    C. Sugar
    D. Air
  8. Air is a:
    A. Compound
    B. Mixture ✔
    C. Element
    D. Suspension
  9. Which method separates dyes?
    A. Filtration
    B. Chromatography ✔
    C. Distillation
    D. Evaporation
  10. Elements are made of:
    A. Molecules
    B. Atoms ✔
    C. Mixtures
    D. Solutions

Exam Tips / Value-Based Questions

Exam Tips

  • Learn definitions clearly.
  • Understand differences between solution, colloid, suspension.
  • Practice separation methods diagrams.
  • Revise examples from daily life.
  • Write answers in points for better marks.

Value-Based Questions

  1. Why should drinking water be purified?
    Answer: To remove harmful impurities and ensure health safety.
  2. Why is separating waste important?
    Answer: Helps recycling and reduces pollution.
  3. Why should we avoid mixing chemicals carelessly?
    Answer: Some mixtures can produce harmful substances.
  4. Why is milk considered nutritious despite being a mixture?
    Answer: It contains essential nutrients beneficial for health.
  5. Why do foggy roads reduce visibility?
    Answer: Due to Tyndall effect scattering light.

Conclusion

The chapter Is Matter Around Us Pure? is one of the most important chapters in Class 9 Chemistry because it builds the foundation for understanding the composition and classification of matter. Everything we see, touch, and use in daily life is made of matter. However, not all matter is pure. This chapter helps students understand the difference between pure substances and mixtures and explains how materials around us are classified based on their composition and properties.

A pure substance contains only one type of particles and has a fixed composition. Elements and compounds are pure substances. Elements are the simplest form of matter and consist of only one type of atom, such as oxygen, iron, and gold. Compounds are formed when two or more elements chemically combine in a fixed ratio. For example, water is formed from hydrogen and oxygen, and sodium chloride is formed from sodium and chlorine. The properties of compounds are different from the properties of the elements that form them.

In contrast, mixtures contain two or more substances physically combined. These substances retain their individual properties and can be separated using physical methods. Air, milk, soil, and saltwater are common examples of mixtures. Understanding mixtures is important because most substances around us are mixtures rather than pure substances.

The chapter Is Matter Around Us Pure? also explains the types of mixtures. Homogeneous mixtures have uniform composition throughout and are called solutions. Salt dissolved in water is an example of a homogeneous mixture. Heterogeneous mixtures have non-uniform composition, such as sand in water or oil mixed with water.

Solutions are an important part of this chapter. A solution is a homogeneous mixture composed of solute and solvent. The solute is the substance that dissolves, while the solvent is the substance that dissolves the solute. Solutions can exist in solid, liquid, or gaseous forms. Understanding the concentration of solutions is also essential. Solutions may be dilute, concentrated, saturated, or unsaturated depending on the amount of solute dissolved.

Another important concept covered in Is Matter Around Us Pure? is colloids and suspensions. Colloids appear uniform but are actually heterogeneous mixtures. They scatter light due to the Tyndall effect and their particles do not settle down. Milk, fog, and smoke are examples of colloids. Suspensions, on the other hand, are heterogeneous mixtures with large particles that settle down when left undisturbed. Muddy water is a common example.

The Tyndall effect is a phenomenon in which light is scattered by particles in a colloid. This effect helps distinguish colloids from true solutions. For example, when sunlight passes through fog or dusty air, the path of light becomes visible due to scattering.

The chapter also highlights various separation techniques used to separate components of mixtures. Filtration is used to separate insoluble solids from liquids. Evaporation is used to separate dissolved solids from liquids. Distillation separates liquids based on differences in boiling points. Chromatography is used to separate dyes and pigments. Centrifugation is used to separate cream from milk. These techniques are used in everyday life, laboratories, and industries.

Understanding the difference between physical and chemical changes is another key concept. In a physical change, no new substance is formed, and the change is usually reversible. Examples include melting ice and dissolving sugar in water. In a chemical change, a new substance is formed and the change is irreversible. Rusting of iron and burning of paper are examples of chemical changes.

The knowledge gained from Is Matter Around Us Pure? is useful in daily life. It helps us understand water purification, food preparation, separation of waste, and industrial processes. It also builds a strong base for advanced chemistry topics in higher classes.

From an examination point of view, this chapter is very important. Students should focus on definitions, differences between key terms, examples, properties of solutions, colloids, suspensions, and separation techniques. Diagrams and examples from everyday life can help in writing better answers.

In conclusion, Is Matter Around Us Pure? helps students understand the nature of matter, the classification of substances, and the methods used to separate mixtures. It connects chemistry concepts with real-life applications and develops scientific thinking. Mastering this chapter not only helps in scoring good marks but also enhances understanding of the material world around us.

Long questions

1. Differentiate between pure substances and mixtures.

Answer:

A pure substance is made up of only one type of particles and has a fixed composition. It shows definite physical and chemical properties. Pure substances cannot be separated into simpler substances by physical methods. Examples include oxygen, gold, and distilled water.

A mixture, on the other hand, consists of two or more substances physically combined. The components retain their individual properties and can be separated using physical methods such as filtration or evaporation. Mixtures do not have a fixed composition. Examples include air, soil, and saltwater.

Key Differences:

  • Pure substances have fixed composition; mixtures do not.
  • Pure substances cannot be separated physically; mixtures can.
  • Pure substances have uniform properties; mixtures may vary.

2. Explain the types of mixtures with examples.

Answer:

Mixtures are classified into two main types:

Homogeneous Mixtures

These mixtures have uniform composition throughout. The components are evenly distributed and cannot be distinguished by naked eye.

Examples: salt solution, air, sugar solution.

Heterogeneous Mixtures

These mixtures have non-uniform composition. The components are visible and unevenly distributed.

Examples: sand in water, oil and water, soil.

Homogeneous mixtures are also called solutions, while heterogeneous mixtures include suspensions and colloids.

3. What is a solution? Explain its components and types.

Answer:

A solution is a homogeneous mixture composed of two components:

  • Solute: the substance that dissolves.
  • Solvent: the substance that dissolves the solute.

Example: In saltwater, salt is the solute and water is the solvent.

Types of Solutions

  1. Solid in liquid – salt in water
  2. Liquid in liquid – alcohol in water
  3. Gas in gas – air (oxygen in nitrogen)
  4. Gas in liquid – carbon dioxide in soda water
  5. Solid in solid – alloys like brass

Solutions are transparent and do not scatter light.

4. Describe the properties of a colloid.

Answer:

A colloid is a heterogeneous mixture that appears homogeneous to the naked eye.

Properties:

  • Particle size is intermediate between solution and suspension.
  • Shows Tyndall effect (scatters light).
  • Particles do not settle down.
  • Cannot be separated by filtration.
  • Stable in nature.

Examples: milk, fog, smoke, butter.

Colloids play an important role in daily life, including food products and medicines.

5. What is a suspension? Write its properties.

Answer:

A suspension is a heterogeneous mixture in which solid particles are dispersed in a liquid and are visible to the naked eye.

Properties:

  • Particles are large and visible.
  • Particles settle down on standing.
  • Can be separated by filtration.
  • Suspension is unstable.
  • Does not transmit light clearly.

Examples: muddy water, chalk powder in water.

6. Explain the Tyndall effect with examples.

Answer:

The Tyndall effect is the scattering of light by particles present in a colloid. When a beam of light passes through a colloidal solution, the path of light becomes visible due to scattering.

Examples:

  • Sunlight passing through fog.
  • Headlights visible in dusty air.
  • Beam of light in a smoky room.

This effect helps distinguish colloids from true solutions.

7. Describe different methods of separating mixtures.

Answer:

Different separation techniques are used depending on the nature of the mixture:

Filtration

Separates insoluble solids from liquids.
Example: separating sand from water.

Evaporation

Removes liquid to obtain dissolved solid.
Example: obtaining salt from seawater.

Distillation

Separates liquids with different boiling points.
Example: separating pure water from saltwater.

Centrifugation

Separates lighter and heavier particles by spinning.
Example: separating cream from milk.

Chromatography

Separates dyes or pigments.
Example: separating colors in ink.

8. Distinguish between compounds and mixtures.

Answer:

A compound is formed when two or more elements chemically combine in a fixed ratio. A mixture is formed when substances combine physically.

Differences:

  • Compounds have fixed composition; mixtures do not.
  • Compounds form new substances; mixtures retain properties.
  • Compounds cannot be separated physically; mixtures can.
  • Example of compound: water (H₂O).
  • Example of mixture: air.

9. Explain the concentration of a solution and its types.

Answer:

The concentration of a solution refers to the amount of solute present in a given quantity of solvent or solution.

Types:

Dilute solution: small amount of solute.
Concentrated solution: large amount of solute.
Saturated solution: cannot dissolve more solute at given temperature.
Unsaturated solution: can dissolve more solute.

Understanding concentration is important in chemistry and daily life.

10. Differentiate between physical and chemical changes with examples.

Answer:

A physical change is a change in which no new substance is formed. It is usually reversible.

Examples: melting ice, dissolving sugar.

A chemical change is a change in which a new substance is formed. It is usually irreversible.

Examples: rusting of iron, burning wood.

Differences:

  • Physical change: no new substance; chemical change: new substance formed.
  • Physical change reversible; chemical change irreversible.
  • Physical change affects physical properties; chemical change affects chemical properties.

Assertion Reason

Directions:
Choose the correct option:

A. Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.

1.

Assertion (A): A pure substance has a fixed composition.
Reason (R): It contains only one type of particles.

Answer: A
Explanation: Pure substances consist of only one type of particles, so their composition remains fixed.

2.

Assertion (A): Air is considered a homogeneous mixture.
Reason (R): Its components are uniformly distributed.

Answer: A
Explanation: Air has uniform composition of gases, making it homogeneous.

3.

Assertion (A): Milk is a true solution.
Reason (R): Milk shows the Tyndall effect.

Answer: D
Explanation: Milk is a colloid, not a true solution. The Tyndall effect confirms colloidal nature.

4.

Assertion (A): Suspensions are unstable mixtures.
Reason (R): Particles settle down on standing.

Answer: A
Explanation: Suspension particles settle down, making them unstable.

5.

Assertion (A): Colloidal particles can be seen with the naked eye.
Reason (R): Their particle size is larger than solutions.

Answer: C
Explanation: Colloidal particles are larger than solution particles but still not visible to the naked eye.

6.

Assertion (A): Salt can be separated from seawater by evaporation.
Reason (R): Water evaporates leaving salt behind.

Answer: A
Explanation: Evaporation removes solvent, leaving the solute.

7.

Assertion (A): All solutions are transparent.
Reason (R): They do not scatter light.

Answer: A
Explanation: True solutions do not scatter light, so they appear transparent.

8.

Assertion (A): A compound has properties different from its constituent elements.
Reason (R): Elements chemically combine in fixed ratios to form compounds.

Answer: A
Explanation: Chemical combination produces new properties.

9.

Assertion (A): Oil and water form a homogeneous mixture.
Reason (R): Oil dissolves completely in water.

Answer: D
Explanation: Oil and water form a heterogeneous mixture; oil does not dissolve in water.

10.

Assertion (A): The Tyndall effect is observed in colloidal solutions.
Reason (R): Colloidal particles scatter light.

Answer: A
Explanation: Light scattering by colloidal particles produces the Tyndall effect.

Case-Based Questions

Case 1: Drinking Water Purification

Riya noticed that her mother boils water before drinking. Sometimes they also use a water purifier to remove impurities.

Questions:

  1. Why is boiling water helpful?
  2. What type of impurities are removed by filtration?
  3. Is purified water a pure substance?

Answers:

  1. Boiling kills harmful microorganisms and makes water safe.
  2. Filtration removes insoluble impurities like dust and sand.
  3. No, purified water may still contain dissolved minerals, so it is not chemically pure.

Case 2: Making Lemonade

A student prepares lemonade by mixing lemon juice, sugar, and water. After stirring, the mixture appears uniform.

Questions:

  1. What type of mixture is lemonade?
  2. Identify solute and solvent.
  3. Why is it called a homogeneous mixture?

Answers:

  1. It is a solution (homogeneous mixture).
  2. Solutes: sugar and lemon juice; solvent: water.
  3. Because the components are evenly distributed.

Case 3: Dust in a Sunbeam

When sunlight enters a room through a small hole, dust particles become visible.

Questions:

  1. Which phenomenon is observed?
  2. Why do dust particles become visible?
  3. Is this effect seen in true solutions?

Answers:

  1. Tyndall effect.
  2. Dust particles scatter light.
  3. No, true solutions do not scatter light.

Case 4: Muddy Water

After rainfall, puddles of muddy water are seen. After some time, mud settles at the bottom.

Questions:

  1. What type of mixture is muddy water?
  2. Why do particles settle down?
  3. Which method can separate mud from water?

Answers:

  1. Suspension.
  2. Because particles are large and heavy.
  3. Filtration or decantation.

Case 5: Milk as a Daily Food

Milk looks uniform but scatters light when a torch is passed through it.

Questions:

  1. What type of mixture is milk?
  2. Why does it scatter light?
  3. Name the effect observed.

Answers:

  1. Colloid.
  2. Due to presence of colloidal particles.
  3. Tyndall effect.

Case 6: Separating Salt from Seawater

Salt is obtained from seawater in coastal areas by allowing water to evaporate.

Questions:

  1. Which separation method is used?
  2. Why does salt remain behind?
  3. Is seawater a mixture or compound?

Answers:

  1. Evaporation.
  2. Water evaporates while salt does not.
  3. It is a mixture.

Case 7: Air Around Us

Air contains nitrogen, oxygen, carbon dioxide, and water vapour.

Questions:

  1. Is air a pure substance or mixture?
  2. Why is air considered homogeneous?
  3. Name one method to separate gases from air.

Answers:

  1. Mixture.
  2. Gases are uniformly mixed.
  3. Fractional distillation.

Case 8: Chalk Powder in Water

When chalk powder is mixed in water, it does not dissolve and settles after some time.

Questions:

  1. What type of mixture is formed?
  2. Why does it settle down?
  3. Can it be separated by filtration?

Answers:

  1. Suspension.
  2. Because particles are large and insoluble.
  3. Yes.

Case 9: Alloy Preparation

Brass is made by mixing copper and zinc.

Questions:

  1. What type of mixture is brass?
  2. Is it homogeneous or heterogeneous?
  3. Why are alloys useful?

Answers:

  1. Solid solution (alloy).
  2. Homogeneous.
  3. They improve strength, durability, and corrosion resistance.

Case 10: Rusting of Iron

An iron gate develops a reddish-brown coating after exposure to moisture and air.

Questions:

  1. Is rusting a physical or chemical change?
  2. Why is a new substance formed?
  3. What is the substance formed called?

Answers:

  1. Chemical change.
  2. Iron reacts with oxygen and moisture.
  3. Rust (iron oxide).

MCQs: Is Matter Around Us Pure?

1. A pure substance contains:

A. Different kinds of particles
B. Only one type of particles ✔
C. Dust particles
D. Impurities

2. Which of the following is a pure substance?

A. Air
B. Milk
C. Copper ✔
D. Soil

3. Air is a:

A. Compound
B. Element
C. Mixture ✔
D. Suspension

4. Which of the following is a compound?

A. Oxygen
B. Water ✔
C. Air
D. Brass

5. Salt dissolved in water forms a:

A. Suspension
B. Colloid
C. Solution ✔
D. Compound

6. The substance that dissolves in a solution is called:

A. Solvent
B. Solute ✔
C. Mixture
D. Colloid

7. The substance that dissolves the solute is called:

A. Solvent ✔
B. Solute
C. Compound
D. Suspension

8. Which mixture has uniform composition?

A. Soil
B. Oil and water
C. Salt solution ✔
D. Sand in water

9. Which of the following is a heterogeneous mixture?

A. Sugar solution
B. Salt solution
C. Sand in water ✔
D. Vinegar

10. Milk is an example of:

A. Solution
B. Suspension
C. Colloid ✔
D. Compound

11. Which mixture shows the Tyndall effect?

A. Salt solution
B. Sugar solution
C. Milk ✔
D. Vinegar

12. The scattering of light by particles is called:

A. Reflection
B. Refraction
C. Tyndall effect ✔
D. Diffusion

13. Which of the following is a suspension?

A. Milk
B. Salt water
C. Muddy water ✔
D. Vineger

14. Particles in a suspension:

A. Are invisible
B. Do not settle
C. Settle down on standing ✔
D. Dissolve completely

15. Which method separates insoluble solids from liquids?

A. Distillation
B. Filtration ✔
C. Evaporation
D. Chromatography

16. Salt can be obtained from seawater by:

A. Filtration
B. Evaporation ✔
C. Centrifugation
D. Distillation

17. Which technique is used to separate dyes?

A. Evaporation
B. Chromatography ✔
C. Filtration
D. Sedimentation

18. Which of the following is a homogeneous mixture?

A. Air ✔
B. Soil
C. Smoke
D. Muddy water

19. Fog is an example of:

A. Suspension
B. Colloid ✔
C. Compound
D. Element

20. Alloys are:

A. Compounds
B. Heterogeneous mixtures
C. Homogenous mixtures ✔
D. Elements

21. Which of the following does NOT scatter light?

A. Milk
B. Fog
C. Sugar solution ✔
D. Smoke

22. A saturated solution:

A. Cannot dissolve more solute ✔
B. Contains no solute
C. Is always dilute
D. Is heterogeneous

23. Which of the following is an element?

A. Brass
B. Oxygen ✔
C. Water
D. Air

24. Brass is a mixture of:

A. Copper and tin
B. Copper and zinc ✔
C. Zinc and iron
D. Iron and carbon

25. Which of the following can be separated by distillation?

A. Sand and water
B. Salt and water
C. Alcohol and water ✔
D. Sugar and salt

26. Colloidal particles:

A. Settle down
B. Are visible to naked eye
C. Scatter light ✔
D. Dissolve completely

27. Which of the following is a chemical change?

A. Melting ice
B. Dissolving sugar
C. Rusting of iron ✔
D. Boiling water

28. Which of the following is a physical change?

A. Burning paper
B. Rusting iron
C. Dissolving sugar ✔
D. Cooking food

29. Which of the following is NOT a mixture?

A. Air
B. Milk
C. Water ✔
D. Soil

30. Which process separates cream from milk?

A. Filtration
B. Distillation
C. Centrifugation ✔
D. Evaporation

Class 9 Chemistry Test Paper

Chapter: Is Matter Around Us Pure?

Time: 1.5 Hours
Maximum Marks: 50

Section A – Very Short Answer (1 × 10 = 10 Marks)

Answer all questions.

  1. Define a pure substance.
  2. Give one example of a homogeneous mixture.
  3. What is a solute?
  4. Name one method to separate insoluble solids from a liquid.
  5. What is a suspension?
  6. Write one example of a colloid.
  7. What is the Tyndall effect?
  8. Name the solvent in a salt solution.
  9. State one property of compounds.
  10. Give one example of a physical change.

Section B – Short Answer Questions (2 × 10 = 20 Marks)

Answer all questions in 30–40 words.

  1. Differentiate between homogeneous and heterogeneous mixtures.
  2. Define solution and give one example.
  3. What is a saturated solution?
  4. State two properties of suspensions.
  5. Give two differences between elements and compounds.
  6. Why do colloids not settle down on standing?
  7. Explain evaporation with an example.
  8. What is an alloy? Give one example.
  9. Why is air considered a mixture?
  10. State two characteristics of pure substances.

Section C – Long Answer Questions (5 × 4 = 20 Marks)

Answer any four questions.

  1. Distinguish between solutions, colloids, and suspensions. Give examples.
  2. Explain different methods of separating mixtures with suitable examples.
  3. What is a solution? Explain the types of solutions with examples.
  4. Differentiate between compounds and mixtures.
  5. Explain the Tyndall effect. How does it help in identifying colloids?
  6. Describe physical and chemical changes with examples.

Internal Choice (Optional Question)

(Attempt instead of any one question from Section C)

  1. Define concentration of a solution. Explain dilute, concentrated, saturated, and unsaturated solutions with examples.

End of Question Paper

Instructions for Students:

  • Write answers in neat and clear points.
  • Use examples wherever possible.
  • Draw diagrams if needed.
  • Revise definitions carefully before submission.

Solutions: Class 9 Chemistry Test Paper

Chapter: Is Matter Around Us Pure?

Maximum Marks: 50

Section A – Very Short Answers

  1. Pure substance: A material made of only one type of particles with fixed composition and definite properties.
  2. Example of homogeneous mixture: Salt dissolved in water.
  3. Solute: The substance that dissolves in a solvent.
  4. Method to separate insoluble solid from liquid: Filtration.
  5. Suspension: A heterogeneous mixture in which solid particles are dispersed in a liquid and settle down on standing.
  6. Example of colloid: Milk.
  7. Tyndall effect: Scattering of light by colloidal particles.
  8. Solvent in salt solution: Water.
  9. Property of compounds: They have fixed composition and properties different from their elements.
  10. Example of physical change: Melting of ice.

Section B – Short Answer Solutions

  1. Homogeneous vs Heterogeneous Mixtures
  • Homogeneous mixtures have uniform composition (salt solution).
  • Heterogeneous mixtures have non-uniform composition (sand in water).
  1. Solution:
    A homogeneous mixture of solute and solvent.
    Example: Sugar dissolved in water.
  1. Saturated Solution:
    A solution that cannot dissolve more solute at a given temperature.
  1. Properties of Suspensions:
  • Particles settle down on standing.
  • Can be separated by filtration.
  1. Elements vs Compounds
  • Elements contain one type of atom; compounds contain two or more elements chemically combined.
  • Elements cannot be broken chemically; compounds can be decomposed.
  1. Why colloids do not settle down:
    Because colloidal particles are very small and remain uniformly dispersed.
  1. Evaporation:
    Process of converting liquid into vapor to obtain dissolved solid.
    Example: Obtaining salt from seawater.
  1. Alloy:
    A homogeneous mixture of metals.
    Example: Brass (copper + zinc).
  1. Why air is a mixture:
    Because it contains different gases (nitrogen, oxygen, carbon dioxide) physically mixed.
  1. Characteristics of pure substances:
  • Fixed composition.
  • Definite physical and chemical properties.

Section C – Long Answer Solutions

21. Difference between Solutions, Colloids, and Suspensions

PropertySolutionColloidSuspension
NatureHomogeneousHeterogeneous (appears uniform)Heterogeneous
Particle sizeVery smallIntermediateLarge
VisibilityNot visibleNot visible to naked eyeVisible
Tyndall effectNoYesYes
SettlingNoNoYes

Examples: salt solution, milk, muddy water.

22. Methods of Separating Mixtures

Filtration: separates insoluble solids (sand from water).
Evaporation: removes liquid (salt from seawater).
Distillation: separates liquids with different boiling points (pure water from saltwater).
Centrifugation: separates cream from milk.
Chromatography: separates dyes and pigments.

23. Solution and Its Types

A solution is a homogeneous mixture of solute and solvent.

Types:

  • Solid in liquid: salt in water
  • Liquid in liquid: alcohol in water
  • Gas in liquid: CO₂ in soda
  • Gas in gas: air
  • Solid in solid: alloys

Solutions are transparent and do not scatter light.

24. Compounds vs Mixtures

  • Compunds are chemically combined; mixtures are physically mixed.
  • Compounds have fixed composition; mixtures vary.
  • Properties of compounds differ from elements; mixtures retain properties.
  • Compounds cannot be separated physically; mixtures can.

Examples: water (compound), air (mixture).

25. Tyndall Effect

The scattering of light by colloidal particles is called the Tyndall effect. When light passes through a colloid, the path of light becomes visible.

Examples: fog, smoke, dusty air.
It helps distinguish colloids from true solutions.

26. Physical vs Chemical Changes

Physical Change

  • No new substance formed
  • Reversible
    Example: melting ice

Chemical Change

  • New substance formed
  • Irreversible
    Example: rusting of iron

Optional Question Solution

27. Concentration of a Solution

Concentration is the amount of solute in a given amount of solution.

Types:

  • Dilute: small amount of solute
  • Concentrated: large amount of solute
  • Saturated: cannot dissolve more solute
  • Unsaturated: can dissolve more solute

Quick Revision Notes: Is Matter Around Us Pure? (Class 9 Chemistry)

The chapter Is Matter Around Us Pure? explains the nature, composition, and classification of substances found around us. In daily life, we use materials like air, milk, water, salt, and sugar. Although many of these appear pure, they are often mixtures. Understanding the difference between pure substances and mixtures is essential for exams and practical applications.

Pure Substances

A pure substance consists of only one type of particles and has a fixed composition and definite properties. It cannot be separated into simpler substances by physical methods.

Pure substances are classified into:

1. Elements
Elements contain only one type of atom and cannot be broken down chemically.
Examples: iron, copper, oxygen, gold.
They are classified as metals, non-metals, and metalloids.

2. Compounds
Compounds are formed when two or more elements chemically combine in a fixed ratio. Their properties differ from the elements that form them.
Examples: water (H₂O), carbon dioxide (CO₂), sodium chloride (NaCl).

Mixtures

A mixture contains two or more substances physically combined. The components retain their individual properties and can be separated by physical methods.

Examples: air, soil, saltwater.

Mixtures are of two types:

Homogeneous Mixtures

  • Uniform composition throughout
  • Components cannot be distinguished
  • Also called solutions
    Examples: salt solution, air, sugar solution

Heterogeneous Mixtures

  • Non-uniform composition
  • Components visible
    Examples: sand in water, oil and water

Solutions

A solution is a homogeneous mixture of solute and solvent.

  • Solute: substance that dissolves
  • Solvent: substance that dissolves the solute

Example: salt (solute) + water (solvent)

Types of solutions:

  • Solid in liquid → salt in water
  • Liquid in liquid → alcohol in water
  • Gas in liquid → CO₂ in soda
  • Gas in gas → air
  • Solid in solid → alloys (brass)

Concentration of solutions:

  • Dilute → small amount of solute
  • Concentrated → large amount
  • Saturated → no more solute dissolves
  • Unsaturated → more solute can dissolve

Colloids

Colloids are mixtures that appear uniform but are actually heterogeneous.

Properties:

  • Show Tyndall effect (scatter light)
  • Particles do not settle
  • Cannot be separated by filtration

Examples: milk, fog, smoke, butter.

Suspensions

Suspensions are heterogeneous mixtures with large visible particles.

Properties:

  • Particles settle on standing
  • Can be filtered
  • Unstable mixtures

Examples: muddy water, chalk powder in water.

Tyndall Effect

The Tyndall effect is the scattering of light by colloidal particles. It helps distinguish colloids from true solutions.

Examples:

  • Sunlight through fog
  • Headlights visible in dusty air

Separation Techniques

Different methods are used to separate mixtures:

  • Filtration → separates insoluble solids
  • Evaporation → separates dissolved solids
  • Distillation → separates liquids with different boiling points
  • Centrifugation → separates cream from milk
  • Chromatography → separates dyes and pigments

Physical and Chemical Changes

Physical Change

  • No new substance formed
  • Usually reversible
    Example: melting ice

Chemical Change

  • New substance formed
  • Usually irreversible
    Example: rusting of iron

Key Differences to Remember

  • Pure substance → fixed composition
  • Mixture → variable composition
  • Solution → homogeneous mixture
  • Colloid → shows Tyndall effect
  • Suspension → particles settle down

Exam Focus Points

  • Differences: mixture vs compound, colloid vs suspension
  • Definitions and examples
  • Separation methods and uses
  • Tyndall effect and real-life examples

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