Questions
1. Which of the following are matter?
Answer:
Chair, air, smell, almonds, cold, lemon water, smell of perfume
These have mass and occupy space, so they are matter.
Love, hate, thought are emotions or feelings — not matter.
2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer:
Particles of matter are constantly moving. In hot food, the particles move faster and spread out quickly due to increased kinetic energy. So, the aroma reaches far. In cold food, particles move slowly, so the smell doesn’t travel far.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer:
This shows that particles of matter have space between them. The diver can move through water because water particles are loosely packed and can be pushed aside.
4. What are the characteristics of the particles of matter?
Answer:
- Particles of matter have space between them.
- Particles of matter are continuously moving.
- Particles of matter attract each other.
5.
(a) The mass per unit volume of a substance is called density.
Formula: Density = Mass / Volume
(b) Arrange in order of increasing density:
Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron
6.
(a) Tabulate the differences in characteristics of states of matter:
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Not fixed | Not fixed |
| Volume | Fixed | Fixed | Not fixed |
| Compressibility | Negligible | Very less | High |
| Rigidity | Rigid | Not rigid | Not rigid |
| Fluidity | Cannot flow | Can flow | Can flow easily |
(b) Comment upon:
- Rigidity: Solids are rigid; liquids and gases are not.
- Compressibility: Gases are highly compressible; liquids slightly; solids almost incompressible.
- Fluidity: Liquids and gases can flow; solids cannot.
- Filling a gas container: Gases completely fill the container.
- Shape: Solids have fixed shape; liquids and gases take shape of the container.
- Kinetic energy: Lowest in solids, more in liquids, highest in gases.
- Density: Usually highest in solids, lower in liquids, lowest in gases.
7. Give reasons:
(a) A gas fills completely the vessel in which it is kept.
Answer:
Gas particles move freely and have negligible force of attraction, so they spread and fill the container.
(b) A gas exerts pressure on the walls of the container.
Answer:
Gas particles move randomly and collide with container walls, exerting pressure.
(c) A wooden table should be called a solid.
Answer:
It has a definite shape, volume, and is rigid—properties of a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer:
Air particles are loosely packed with lots of space between them, allowing movement. Wood particles are tightly packed, resisting movement.
8 . Liquids generally have lower density than solids. But ice floats on water. Find out why.
Answer:
Ice has a cage-like structure due to hydrogen bonding, creating more empty spaces. This makes ice less dense than liquid water, so it floats.
9. Convert the following temperature to Celsius scale:
Formula:
°C = K − 273
- (a) 300 K = 27°C
- (b) 573 K = 300°C
10. What is the physical state of water at:
- (a) 250°C – Vapour (since it is well above the boiling point of water, 100°C)
- (b) 100°C – Both liquid and vapour (this is the boiling point, where both states coexist during phase change)
11. For any substance, why does the temperature remain constant during the change of state?
Answer:
During a change of state, the heat energy supplied is used to overcome the forces of attraction between the particles, not to increase their kinetic energy. Hence, the temperature remains constant.
12. Suggest a method to liquefy atmospheric gases.
Answer:
By increasing pressure and lowering the temperature, atmospheric gases can be liquefied. This reduces the kinetic energy of gas molecules and brings them closer together.
13. Why does a desert cooler cool better on a hot dry day?
Answer:
Because on a hot dry day, the rate of evaporation is higher. More water evaporates from the cooler’s pads, taking away more heat and cooling the air more effectively.
14. How does the water kept in an earthen pot (matka) become cool during summer?
Answer:
Water seeps out through the pores of the earthen pot and evaporates. This evaporation requires heat, which is taken from the water inside, making it cool.
15. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer:
These substances evaporate quickly. During evaporation, they absorb heat from our palm, making it feel cold.
16. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer:
A saucer has a larger surface area, so the tea or milk cools faster due to quicker evaporation.
17. What type of clothes should we wear in summer?
Answer:
We should wear light-colored, loose, and cotton clothes in summer because they reflect heat and absorb sweat, helping it evaporate and cool the body.
Exercises
1. Convert the following temperatures to the Celsius scale:
(a) 293 K = 293 − 273 = 20°C
(b) 470 K = 470 − 273 = 197°C
2. Convert the following temperatures to the Kelvin scale:
(a) 25°C = 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K
3. Give reason for the following observations:
(a) Naphthalene balls disappear with time without leaving any solid because they directly change from solid to gas (sublimation).
(b) We can smell perfume from a distance because its particles diffuse quickly through air.
4. Arrange in increasing order of force of attraction between particles:
Oxygen < Water < Sugar
5. Physical state of water at:
(a) 25°C — Liquid
(b) 0°C — Solid and Liquid (in equilibrium)
(c) 100°C — Liquid and Gas (in equilibrium)
6. Justify:
(a) Water at room temperature is a liquid:
- It has a definite volume but no definite shape.
- The intermolecular force is moderate, allowing flow.
(b) Iron almirah is solid at room temperature:
- It has a fixed shape and volume.
- Strong intermolecular forces keep the particles tightly packed.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Because ice absorbs extra heat (latent heat of fusion) to melt into water, thus drawing more heat and cooling more effectively.
8. What produces more severe burns, boiling water or steam?
Steam, because it carries latent heat of vaporization in addition to its temperature.
9. Name A, B, C, D, E, F in the diagram:
- A = Fusion (Melting)
- B = Vaporization (Boiling)
- C = Condensation
- D = Solidification (Freezing)
- E = Sublimation
- F = Deposition
Exemplar Problems
1. Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases
Answer:
(c) Evaporation, diffusion, expansion of gases
2. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
Answer:
(c) Low temperature, high pressure
3. The property to flow is unique to fluids. Which one of the following statements is correct?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids
Answer:
(c) Gases and liquids behave like fluids
4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation
Answer:
(d) evaporation
5. A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air
Answer:
(c) Oxygen, water, sugar
6. On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K
Answer:
(d) 298 K, 310 K and 338 K
7. Choose the correct statement of the following
(a) conversion of solid into vapours without passing through the liquid state is called sublimation.
(b) conversion of vapours into solid without passing through the liquid state is called vapourisation.
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.
Answer:
(a) conversion of solid into vapours without passing through the liquid state is called sublimation.
8. The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K
Answer:
(c) 308 K, 329 K, 391 K
9. Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water
Answer:
(a) Increase in temperature of water
10. In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas
(iv) Adding more hydrogen gas to the container without increasing the volume of the container
Options:
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer:
(c) (ii) and (iii)
11. A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.
Answer:
No, the water is not pure.
Pure water boils at exactly 100°C at normal pressure. A boiling point of 102°C suggests the presence of impurities, which raise the boiling point (boiling point elevation).
Similarly, the freezing point of impure water would be lower than 0°C (freezing point depression), so this water may not freeze at 0°C.
12. Which graph correctly represents the temperature change when heating ice and water in a beaker?
Answer
Correct graph: (d)
Explanation:
Let’s examine what’s happening in this situation:
- Initially there’s ice and water. The temperature is at 0°C and stays constant while ice melts.
- Once all ice has melted, only water remains, and the temperature starts increasing.
- When the water reaches 100°C, if we continue heating, temperature stays at 100°C until it completely boils.
Now check Graph (d):
- Starts flat at 0°C (melting).
- Then temperature rises (water heats).
- Then flat again at 100°C (boiling).
So option (d) is correct
13. Fill in the blanks:
Answer:
(a) Evaporation of a liquid at room temperature leads to a cooling effect.
Explanation: During evaporation, particles with higher energy escape, lowering the average kinetic energy and cooling the surface.
(b) At room temperature the forces of attraction between the particles of solid substances are stronger than those in the gaseous state.
Explanation: Solids have tightly packed particles, unlike gases.
(c) The arrangement of particles is less ordered in the liquid state. However, there is no order in the gaseous state.
Explanation: Liquids have some particle arrangement; gases have none.
(d) Sublimation is the change of solid state directly to vapour state without going through the liquid state.
Explanation: Examples: camphor, dry ice.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called evaporation.
Explanation: It occurs at the surface of the liquid, not throughout.
14. Match the physical quantities (A) to their SI units (B):
| A (Quantity) | B (SI Unit) | Answer |
|---|---|---|
| (a) Pressure | (iii) Pascal | a → iii |
| (b) Temperature | (iv) Kelvin | b → iv |
| (c) Density | (v) Kilogram/m³ | c → v |
| (d) Mass | (ii) Kilogram | d → ii |
| (e) Volume | (i) Cubic metre | e → i |
15. Match the non-SI and SI units:
| A (Non-SI Unit) | B (SI Unit) | Answer |
|---|---|---|
| (a) Degree Celsius | (iv) Kelvin | a → iv |
| (b) Centimetre | (iii) Metre | b → iii |
| (c) Gram per cm³ | (v) Kilogram per m³ | c → v |
| (d) Bar | (ii) Pascal | d → ii |
| (e) Milligram | (i) Kilogram | e → i |
Explanation:
- °C and K both measure temperature
- cm and m are length units
- g/cm³ and kg/m³ are for density
- Bar and Pascal are pressure units
- mg and kg are mass units (non-SI and SI)
16. ‘Osmosis is a special kind of diffusion’. Comment.
Answer
Yes, in both phenomena, particles move from a region of higher concentration to a region of lower concentration. However, in osmosis, the movement specifically involves the solvent passing through a semi-permeable membrane that allows only water molecules to pass through.
The dissolution of gases in water (like oxygen in lakes or carbon dioxide in soda) is also a result of diffusion, but it might seem less intuitive to identify “higher” and “lower” concentration regions. Here’s how it works:
Validation of higher to lower concentration:
- Before dissolution: The concentration of the gas (say, CO₂) is higher in the air above the water surface and lower in the water.
- During diffusion: Gas molecules move from the air (higher concentration) into the water (lower concentration) until equilibrium is reached.
- At equilibrium: The rate of gas entering the water equals the rate leaving it.
Aquatic Life – Dissolved Oxygen
- Higher concentration: Oxygen in the atmosphere.
- Lower concentration: Oxygen in the water (especially if it’s warm or polluted).
- What happens: Oxygen diffuses from air into water.
- Why it matters: Fish and aquatic organisms rely on this dissolved oxygen. If the air has more oxygen (like after a rainfall), more dissolves into the water.
Soda Fizzing – Carbon Dioxide Escape
- Inside the bottle: High concentration of CO₂ (dissolved under pressure).
- Outside the bottle (after opening): Low CO₂ in the air.
- What happens: CO₂ diffuses out from the drink into the air — you see it as fizz and bubbles.
17. Identify the following into osmosis/diffusion
Answer
Let’s classify each:
(a) Swelling up of a raisin on keeping in water — Osmosis
(b) Spreading of virus on sneezing — Diffusion
(c) Earthworm dying on coming in contact with common salt - Osmosis
(d) Shrinking of grapes kept in thick sugar syrup — Osmosis
(e) Preserving pickles in salt — Osmosis
(f) Spreading of smell of cake being backed throughout the house — Diffusion
(g) Aquatic animals using oxygen dissolved in water during respiration — Diffusion
18. Water as ice has a cooling effect, whereas steam may cause burns. Explain.
Answer:
Ice absorbs latent heat of fusion from the skin to melt, causing a cooling effect.
Steam contains latent heat of vaporization, which is released when it condenses on skin — this is more than the heat at 100°C, hence it causes burns.
19. Alka was making tea… she wondered why the steam temperature was higher. Comment.
Answer:
Yes, steam has more heat energy than boiling water due to latent heat of vaporization. Even though both are at 100°C, steam stores extra energy which it releases upon condensation — making it feel hotter.
20.
Hot water tumbler kept in freezer. Which graph (Fig. 1.2) is correct?
Correct Answer: (a)
Explanation:
- Initially, water cools till 0°C
- Then it freezes, temperature remains constant
- Then ice temperature falls below 0°C
Graph (a) shows this cooling–freezing–further cooling sequence.
21. Which vessel (A, B, C, D) will have the highest evaporation?
Correct Answer: C (vessel under fan and with a wide mouth)
Explanation:
- Evaporation increases with surface area, air movement, and temperature.
- Vessel C has maximum surface area and a fan blowing air above it — which speeds up evaporation.
22.
(a) Conversion of solid to vapour: Sublimation
Conversion of vapour to solid: Deposition
(b) Conversion of solid to liquid: Fusion
Latent heat of fusion is the heat required to break the force of attraction between solid particles to convert into liquid without raising temperature.
23. You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well-labelled diagram.
Answer:
To separate a mixture of naphthalene and ammonium chloride, we can use a combination of filtration and evaporation based on their solubility:
- Add water to the mixture.
- Ammonium chloride dissolves in water.
- Naphthalene does not dissolve in water.
- Filtration:
- Pour the mixture into a funnel with filter paper.
- Naphthalene remains on the filter paper as residue.
- Ammonium chloride solution passes through as filtrate.
- Evaporation:
- Heat the filtrate gently in an evaporating dish.
- Water evaporates, leaving behind ammonium chloride crystals.
24. It is a hot summer day. Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?
Answer:
Priyanshi would be more comfortable because:
- Cotton is a good absorber of sweat and allows it to evaporate easily.
- Evaporation causes cooling, making the body feel cooler.
- Nylon, being synthetic, does not absorb sweat well and can feel sticky and hot.
25. You want to wear your favourite shirt to a party, but the problem is that it is still wet after a wash. What steps would you take to dry it faster?
Answer:
To dry the shirt faster:
- Spread it to increase surface area.
- Keep it in a place with good airflow, e.g., under a fan.
- Wring the shirt to remove excess water.
- Expose it to sunlight to increase temperature and promote evaporation.
- Choose a dry, less humid location.
26. Comment on the following statements:
(a) Evaporation produces cooling.
Yes. During evaporation, the liquid particles absorb heat from surroundings (including our body) to change into vapour, causing cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
Correct. High humidity means the air already has a lot of water vapour, so the rate of evaporation slows down due to reduced moisture absorption capacity of the air.
(c) Sponge though compressible is a solid.
True. A sponge has pores filled with air, which can be compressed. However, the material of the sponge has a definite shape and volume, which are properties of a solid.
Q27. Why does the temperature of a substance remain constant during its melting point or boiling point?
Answer:
At the melting or boiling point, the heat supplied is used to overcome the forces of attraction between the particles — not to increase kinetic energy.
Thus, temperature remains constant until the entire substance has changed its state.
Diffusion vs Osmosis
Preservation of Pickles – Osmosis & Antimicrobial Action
- Salt draws water out of the pickle ingredients (like mangoes or lemons) by osmosis.
- This reduces moisture inside the food, making it harder for microbes to survive.
- The high concentration of salt in the brine (pickle solution) creates a hypertonic environment.
- Microorganisms that spoil food cannot survive or multiply in such salty conditions because water leaves their cells, leading to dehydration and death (just like the earthworm).
Result:
- Salt prevents bacterial and fungal growth.
- Pickles stay fresh and safe for months or even years.
Earthworm dying due to contact with common salt – Osmosis
- Earthworms have moist, semi-permeable skin through which they exchange gases and water.
- When salt is sprinkled on them, it draws water out of their body due to osmosis.
What Happens:
- The salt creates a highly concentrated solution outside the worm.
- Water inside the worm’s body moves outward to balance the concentration.
- This rapid water loss leads to dehydration, disturbing the worm’s physiological processes.
Here’s how salt creates a highly concentrated solution:
- Salt (NaCl) is hygroscopic – it absorbs moisture from the surroundings.
- When sprinkled on an earthworm, salt dissolves in the moisture on the worm’s skin, forming a concentrated salt solution right there on the surface.
- This solution now has a very high solute concentration (salt) and very low water concentration.
- By osmosis, water from inside the worm’s cells moves outward into this salty solution to balance the concentration.
Result:
- The worm dries out and dies due to excessive loss of water.