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These are complete exercise solutions for Samacheer Kalvi 9th Science Chapter 1 — Matter Around Us. Solve each question yourself first, then verify your method and answer below. Focus on understanding the concept, not just memorising the answer.
Key Concepts (Quick Recap)
- Matter: Anything that occupies space and has mass. Made up of particles (atoms/molecules) that are continuously moving, have spaces between them, and attract each other.
- States of matter: Solid (fixed shape and volume), Liquid (fixed volume, takes shape of container), Gas (no fixed shape or volume).
- Interconversion of states: Melting (solid → liquid), Freezing/Solidification (liquid → solid), Evaporation (liquid → gas), Condensation (gas → liquid), Sublimation (solid → gas directly), Deposition (gas → solid directly).
- Effect of temperature: Increases kinetic energy of particles, changes state from solid → liquid → gas.
- Effect of pressure: Compresses gases; increasing pressure can liquefy a gas (e.g., LPG).
- Elements, Compounds, Mixtures: Elements = one type of atom; Compounds = two or more elements chemically combined in fixed ratio; Mixtures = two or more substances physically mixed.
- Separation techniques: Filtration, distillation, evaporation, sublimation, chromatography, centrifugation, fractional distillation.
- Atoms and Molecules: Atom = smallest particle of an element; Molecule = two or more atoms chemically bonded.
I. Choose the Correct Answer (MCQs)
Q1. Which of the following is NOT a property of solids? (a) Fixed shape (b) Fixed volume (c) High compressibility ✓ (d) Particles closely packed
Answer(c) ✓ — Solids have very low compressibility because particles are tightly packed with negligible intermolecular spaces. They cannot be compressed easily.
Q2. The process of conversion of solid directly into gas is called: (a) Evaporation (b) Condensation (c) Sublimation ✓ (d) Melting
Answer(c) ✓ — Sublimation is the direct transition from solid to gas without passing through the liquid state. Examples: camphor, naphthalene, dry ice.
Q3. Which of the following has the maximum intermolecular space? (a) Iron block (b) Water (c) Oxygen gas ✓ (d) Salt crystal
Answer(c) ✓ — Gases have the maximum intermolecular spaces. Oxygen gas, being a gas, has far greater spaces between particles than solids (iron, salt) or liquids (water).
Q4. Which of the following is an element? (a) Water (b) Common salt (c) Iron ✓ (d) Sugar
Answer(c) ✓ — Iron (Fe) is a single type of atom and hence an element. Water (H₂O), common salt (NaCl), and sugar (C₁₂H₂₂O₁₁) are compounds.
Q5. The boiling point of water at standard atmospheric pressure is: (a) 0 °C (b) 50 °C (c) 100 °C ✓ (d) 373 °C
Answer(c) ✓ — At 1 atm (101.3 kPa), water boils at 100 °C. Note: 373 °C would correspond to 373 K on the Kelvin scale, which equals 100 °C — but the question asks for the Celsius value.
Q6. Which separation technique is used to separate two miscible liquids with different boiling points? (a) Filtration (b) Distillation ✓ (c) Centrifugation (d) Sublimation
Answer(b) ✓ — Distillation (specifically fractional distillation) separates miscible liquids based on their different boiling points. The liquid with the lower boiling point evaporates first and is collected by condensation.
Q7. A substance that sublimes is: (a) Ice (b) Wax (c) Camphor ✓ (d) Sugar
Answer(c) ✓ — Camphor sublimes — it changes directly from solid to gas. Ice melts first then evaporates. Wax melts. Sugar decomposes on heating.
Q8. Which state of matter has neither fixed shape nor fixed volume? (a) Solid (b) Liquid (c) Gas ✓ (d) Both (b) and (c)
Answer(c) ✓ — Gases have neither fixed shape nor fixed volume. They fill the entire container. Liquids have fixed volume but take the shape of the container.
Q9. The process of conversion of liquid into solid is called: (a) Melting (b) Freezing ✓ (c) Condensation (d) Evaporation
Answer(b) ✓ — Freezing (or solidification) is the change from liquid to solid. Example: Water freezing into ice at 0 °C.
Q10. Which of the following is a mixture? (a) Distilled water (b) Air ✓ (c) Common salt (d) Iron
Answer(b) ✓ — Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour, and other gases. The components can be separated by fractional distillation of liquid air.
II. Fill in the Blanks
1. Anything that occupies space and has mass is called matter. 2. The change of state from liquid to gas is called evaporation (or vapourisation). 3. The intermolecular force of attraction is maximum in solids. 4. The SI unit of temperature is kelvin (K). 5. The process of conversion of gas into liquid is called condensation. 6. Ammonium chloride is an example of a substance that undergoes sublimation. 7. The space between particles is maximum in gases. 8. A homogeneous mixture of two or more metals is called an alloy. 9. The temperature at which a solid changes into liquid at atmospheric pressure is called its melting point. 10. Evaporation causes cooling because the high-energy molecules escape from the liquid surface.
III. True or False
1. Evaporation is a surface phenomenon.
AnswerTrue — Evaporation occurs only at the surface of a liquid, unlike boiling which occurs throughout the liquid.
2. Solids have large intermolecular spaces.
AnswerFalse — Solids have very small intermolecular spaces; particles are tightly packed. Gases have large intermolecular spaces.
3. Gases can be compressed easily.
AnswerTrue — Gases have large intermolecular spaces, so they can be compressed significantly by applying pressure.
4. Boiling is a slow process and occurs at all temperatures.
AnswerFalse — Boiling is a rapid process that occurs at a specific temperature (boiling point). It is evaporation that is slow and occurs at all temperatures.
5. A mixture can be separated by physical methods.
AnswerTrue — The components of a mixture can be separated by physical methods like filtration, distillation, chromatography, etc., because they are not chemically bonded.
6. An element is made up of only one kind of atom.
AnswerTrue — By definition, an element consists of only one type of atom. Examples: Hydrogen (H), Oxygen (O), Iron (Fe).
7. Increasing pressure decreases the melting point of ice.
AnswerTrue — For ice, increasing pressure lowers the melting point (regelation). This is why ice melts under pressure (e.g., ice skating).
8. Latent heat of vapourisation is the heat required to convert a solid into liquid.
AnswerFalse — Latent heat of vapourisation converts liquid to gas. Latent heat of fusion (melting) converts solid to liquid.
9. In a compound, the constituents can be separated by simple physical methods.
AnswerFalse — Compounds have constituents chemically bonded in fixed ratios; they can only be separated by chemical methods, not physical ones.
10. The kinetic energy of particles increases with increase in temperature.
AnswerTrue — Temperature is a measure of average kinetic energy. As temperature rises, particles move faster and their kinetic energy increases.
IV. Match the Following
| Column I | Column II |
|---|
| 1. Solid → Liquid | (C) Melting |
| 2. Liquid → Gas | (E) Vapourisation |
| 3. Gas → Liquid | (F) Condensation |
| 4. Liquid → Solid | (A) Freezing |
| 5. Solid → Gas | (D) Sublimation |
| 6. Gas → Solid | (B) Deposition |
V. Assertion and Reason
Q1. A: Evaporation causes cooling. R: The molecules with higher kinetic energy escape from the liquid surface, lowering the average kinetic energy. → (a) Both A and R are true, and R is the correct explanation. When high-energy molecules leave, the remaining molecules have lower average kinetic energy, which means lower temperature — hence cooling.
Q2. A: Gases exert pressure on the walls of the container. R: Gas molecules are stationary and do not collide with the walls. → (c) A is true but R is false. Gas molecules move rapidly in all directions and collide with the container walls, exerting pressure. They are NOT stationary.
Q3. A: A compound cannot be separated into its constituents by physical methods. R: The constituents of a compound are chemically bonded. → (a) Both A and R are true, and R is the correct explanation. Since constituents are chemically bonded in a compound, physical methods like filtration or distillation cannot separate them.
VI. Short Answers
Q1. Define matter. Give two examples.
Answer
Matter is anything that occupies space and has mass. It is made up of particles that are continuously moving, have spaces between them, and attract each other. Examples: A book (solid), water (liquid), air (gas).
Q2. What are the characteristics of particles of matter?
Answer
1. Particles have spaces between them — demonstrated by dissolving sugar in water (level doesn't rise proportionally). 2. Particles are continuously moving — demonstrated by diffusion (e.g., spreading of perfume). 3. Particles attract each other — intermolecular force of attraction holds particles together; strongest in solids, weakest in gases.
Q3. Differentiate between solid, liquid, and gas.
Answer
| Property | Solid | Liquid | Gas |
|---|
| Shape | Fixed | Takes container shape | Takes container shape |
| Volume | Fixed | Fixed | No fixed volume |
| Compressibility | Negligible | Very low | High |
| Intermolecular force | Very strong | Moderate | Very weak |
| Intermolecular space | Very small | Moderate | Very large |
| Particle movement | Vibrate at fixed positions | Slide past each other | Move freely in all directions |
| Diffusion | Very slow | Moderate | Fast |
| Example | Iron, ice | Water, milk | Oxygen, CO₂ |
Q4. What is sublimation? Give two examples.
Answer
Sublimation is the process in which a solid changes directly into the gaseous state without passing through the liquid state, on heating. Examples: (1) Camphor — disappears on heating without leaving liquid. (2) Ammonium chloride — sublimes on heating and deposits on the cooler part of the test tube.
Q5. Why does a gas fill the entire container?
Answer
Gas particles have very weak intermolecular forces and very high kinetic energy. They move freely and randomly in all directions at high speeds. Since there are negligible forces holding them together, they spread out and fill the entire volume of the container they are placed in.
Q6. What is the effect of temperature on the state of matter?
Answer
When temperature increases, the kinetic energy of particles increases. This weakens the intermolecular forces and increases the distance between particles. As a result:
Conversely, decreasing temperature reduces kinetic energy, strengthens intermolecular forces, and causes gas → liquid → solid transitions.
- A solid changes to liquid (melting) at its melting point.
- A liquid changes to gas (boiling/vapourisation) at its boiling point.
Q7. Differentiate between evaporation and boiling.
Answer
| Property | Evaporation | Boiling |
|---|
| Temperature | Occurs at all temperatures | Occurs at a fixed temperature (boiling point) |
| Location | Only at the liquid surface | Throughout the liquid |
| Speed | Slow process | Rapid process |
| Bubbles | No bubbles formed | Bubbles formed throughout |
| Nature | Surface phenomenon | Bulk phenomenon |
VII. Detailed Answers
Q1. Explain the interconversion of states of matter with a diagram and examples.
Answer
Matter can change from one state to another by changing temperature or pressure. The five key interconversions are:
1. Melting (Fusion): Solid → Liquid. Heat energy overcomes intermolecular forces. Example: Ice (0 °C) melts into water. 2. Freezing (Solidification): Liquid → Solid. Removal of heat reduces particle energy. Example: Water freezes into ice at 0 °C. 3. Vapourisation (Evaporation/Boiling): Liquid → Gas. Particles gain enough energy to escape. Example: Water boils into steam at 100 °C. 4. Condensation (Liquefaction): Gas → Liquid. Cooling reduces kinetic energy. Example: Water vapour condenses on a cold surface to form dew. 5. Sublimation: Solid → Gas (direct). Example: Camphor, naphthalene, dry ice (solid CO₂). 6. Deposition: Gas → Solid (direct). Example: Formation of frost from water vapour on cold surfaces.
The entire cycle can be represented as:
Solid ↔ Liquid ↔ Gas Solid → Gas (Sublimation) Gas → Solid (Deposition)
Each transition involves either absorption of heat (melting, vapourisation, sublimation) or release of heat (freezing, condensation, deposition). The amount of heat required for the transition is called latent heat (of fusion or of vapourisation).
Q2. Explain the factors affecting evaporation and how evaporation causes cooling.
Answer
Factors affecting evaporation:
1. Temperature: Higher temperature increases evaporation because more molecules have enough kinetic energy to escape from the liquid surface. 2. Surface area: Larger surface area increases evaporation. That is why clothes dry faster when spread out than when folded. 3. Humidity: Higher humidity (more water vapour in air) decreases evaporation because the air is already nearly saturated. Clothes dry slower on a rainy day. 4. Wind speed: Higher wind speed increases evaporation by carrying away water vapour from the surface, preventing saturation. That is why clothes dry faster on a windy day. 5. Nature of liquid: Volatile liquids (like petrol, alcohol) evaporate faster than less volatile liquids (like water) because they have lower boiling points and weaker intermolecular forces.
How evaporation causes cooling:
Evaporation is a surface phenomenon where molecules with higher kinetic energy escape from the liquid surface into the air. When these high-energy molecules leave, the average kinetic energy of the remaining molecules decreases. Since temperature is a measure of average kinetic energy, the liquid becomes cooler.
Everyday examples:
- We feel cool when sweat evaporates from our skin.
- Water in an earthen pot (matka) stays cool because evaporation from the pot's porous surface absorbs heat.
- Acetone (nail polish remover) feels cold on the skin because it evaporates rapidly.
Q3. Differentiate between elements, compounds, and mixtures with examples.
Answer
| Property | Element | Compound | Mixture |
|---|
| Definition | Made of only one kind of atom | Made of two or more elements chemically combined in a fixed ratio | Two or more substances physically mixed in any ratio |
| Composition | One type of atom only | Fixed ratio of elements (e.g., H₂O always 2:1) | Variable composition |
| Separation | Cannot be broken down further by chemical methods | Can be separated only by chemical methods | Can be separated by physical methods (filtration, distillation, etc.) |
| Properties | Properties of constituent atoms | Properties differ from constituent elements | Properties of individual constituents are retained |
| Energy change | — | Formation involves energy change (exothermic or endothermic) | No energy change on mixing |
| Melting/Boiling point | Fixed | Fixed | Not fixed (varies with composition) |
| Examples | Iron (Fe), Oxygen (O₂), Gold (Au), Carbon (C) | Water (H₂O), Common salt (NaCl), Carbon dioxide (CO₂) | Air, salt water, sand + iron filings, salad |
Why water is a compound and not a mixture:
- Hydrogen and oxygen combine in a fixed ratio of 2:1 by volume (1:8 by mass).
- The properties of water are entirely different from those of hydrogen and oxygen.
- Water cannot be separated into hydrogen and oxygen by physical methods.
- Energy is released when water is formed from hydrogen and oxygen.
Common Mistakes
1. Confusing melting and sublimation — Melting is solid → liquid; sublimation is solid → gas directly. Camphor sublimes, ice melts. 2. Saying gases have fixed volume — Gases have NO fixed volume; they expand to fill the container. Only solids and liquids have fixed volume. 3. Confusing element and compound — An element has one type of atom (e.g., Fe). A compound has two or more elements chemically bonded in a fixed ratio (e.g., H₂O). 4. Saying evaporation and boiling are the same — Evaporation is a slow surface phenomenon at all temperatures; boiling is a rapid bulk phenomenon at a fixed temperature. 5. Confusing latent heat of fusion and latent heat of vapourisation — Latent heat of fusion = heat needed for solid → liquid (ice → water). Latent heat of vapourisation = heat needed for liquid → gas (water → steam). 6. Forgetting that condensation is the reverse of evaporation — Condensation = gas → liquid. It releases heat, whereas evaporation absorbs heat. 7. Saying "air is a compound" — Air is a mixture (of N₂, O₂, CO₂, etc.) with variable composition. Its components can be separated by fractional distillation of liquid air. 8. Confusing intermolecular force and intermolecular space — Solids have the strongest intermolecular forces AND the smallest intermolecular spaces. Gases have the weakest forces AND the largest spaces. They are inversely related.
Exam Checklist
- [ ] Definitions of matter, solid, liquid, gas memorised with examples
- [ ] Properties of particles of matter (space, movement, attraction) with demonstrations
- [ ] State interconversions: names, direction, and examples (melting, freezing, vapourisation, condensation, sublimation, deposition)
- [ ] Latent heat of fusion vs latent heat of vapourisation — definitions and numerical meaning
- [ ] Factors affecting evaporation (temperature, surface area, humidity, wind speed)
- [ ] Evaporation causes cooling — explain with examples
- [ ] Differences: element vs compound vs mixture (with examples)
- [ ] Difference: evaporation vs boiling (table format)
- [ ] Difference: solid vs liquid vs gas (table format)
- [ ] Separation techniques and when to use each (filtration, distillation, sublimation, chromatography, centrifugation)
- [ ] Assertion-Reason technique: check A independently, check R independently, then check if R explains A
Internal Links
- [Chapter 1 Guide — Matter Around Us](/school/tamil-nadu-state-board/class/9/science/matter-around-us)
- [All Class 9 Science Solutions](/school/tamil-nadu-state-board/class/9/science/solutions)
- [Class 9 Science Subject Guide](/school/tamil-nadu-state-board/class/9/science)
