CBSE Class 9 Science Matter in our sorroundings Sure Shot Questions Set 03

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1. Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid. [1 Mark]

Answer:
1. The conversion of vapour to solid is called deposition or sublimation (sometimes referred to as solid-state condensation).
2. Deposition is the reverse process of sublimation where gas transforms directly into solid without passing through the liquid state.

Teacher's Note:
a) Sublimation and deposition are phase transitions that bypass the liquid state entirely.
b) Iodine vapour forming iodine crystals on a cold surface is a common example of deposition.

2. Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion? [2 Marks]

Answer:
1. Latent heat of fusion is the amount of heat energy required to change \(1\text{ kg}\) of a solid into liquid at atmospheric pressure at its melting point.
2. The word latent means hidden because this heat energy is absorbed by the solid without showing any rise in temperature.

Teacher's Note:
a) This energy is used to overcome the forces of attraction between particles holding them in a fixed solid state.
b) Particles in water at \(0^\circ\text{C}\) have more energy than particles in ice at \(0^\circ\text{C}\) due to this latent heat absorption.

3. Fill in the blanks: [5 Marks]
(a) Evaporation of a liquid at room temperature leads to a - - - effect.
(b) At room temperature the forces of attraction between the particles of solid substances are - - - than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the - - - state. However, there is no order in the - - - state.
(d) - - - is the change of gaseous state directly to solid state without going through the - - - state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called - - - .

Answer:
(a) cooling
(b) stronger
(c) liquid, gaseous
(d) Deposition, liquid
(e) evaporation

Teacher's Note:
a) Evaporation causes cooling because particles absorb energy from the surroundings to regain the kinetic energy lost during vaporization.
b) Solids have maximum inter-particle attraction, whereas gases have negligible attraction forces between their particles.
c) Always remember that the gaseous state has completely random and disordered movement of particles.

4. Match the physical quantities given in column A to their S I units given in column B : [5 Marks]

Answer:
(a) - (iii) pascal
(b) - (iv) kelvin
(c) - (v) kilogram per cubic metre
(d) - (ii) kilogram
(e) - (i) cubic metre

Teacher's Note:
a) SI units are standardized international units used for scientific measurements.
b) Pressure is measured in Pascals (\(\text{Pa}\)), and density is mass divided by volume (\(\text{kg/m}^3\)).

5. The non S I and S I units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity: [5 Marks]

Answer:
(a) - (iv) kelvin
(b) - (iii) metre
(c) - (v) kilogram per metre cube
(d) - (ii) pascal
(e) - (i) kilogram

Teacher's Note:
a) Degree Celsius and Kelvin are both units used to measure temperature.
b) Bar and Pascal are both units used to measure pressure.

6. Classify the following into osmosis/diffusion [7 Marks]
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked through out the house.
(g) Aquatic animals using oxygen dissolved in water during respiration.

Answer:
1. (a) Swelling up of a raisin on keeping in water - Osmosis
2. (b) Spreading of virus on sneezing - Diffusion
3. (c) Earthworm dying on coming in contact with common salt - Osmosis
4. (d) Shrinking of grapes kept in thick sugar syrup - Osmosis
5. (e) Preserving pickles in salt - Osmosis
6. (f) Spreading of smell of cake being baked through out the house - Diffusion
7. (g) Aquatic animals using oxygen dissolved in water during respiration - Diffusion

Teacher's Note:
a) Osmosis is a special type of diffusion involving the movement of water molecules through a semi-permeable membrane.
b) Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration without any membrane requirement.
c) Salt application creates a hypertonic medium, causing water to move out of biological cells via osmosis leading to plasmolysis or death of cells.

7. Which one of the following sets of phenomena would increase on raising the temperature? [1 Mark]
(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

1. Raising temperature increases the kinetic energy of particles.
2. Higher kinetic energy causes faster evaporation, rapid diffusion, and expansion of gases.
3. Compression of gases decreases with an increase in temperature.
4. Hence, the correct option is (C).

Teacher's Note:
a) Temperature is directly proportional to particle kinetic energy.
b) Gases expand and compress less easily at higher temperatures due to increased molecular motion.

8. 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 [1 Mark]
(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

1. Gases can be liquefied by bringing their particles closer together.
2. High pressure decreases the distance between gas molecules.
3. Low temperature decreases the kinetic energy so molecules do not fly apart.
4. Hence, the correct option is (C).

Teacher's Note:
a) Applying high pressure reduces interparticle space.
b) Lowering temperature reduces particle speed, facilitating liquefaction.

9. The property to flow is unique to fluids. Which one of the following statements is correct? [1 Mark]
(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

1. Both liquids and gases have the ability to flow.
2. Substances that can flow are collectively called fluids.
3. Solids do not possess the property to flow.
4. Hence, the correct option is (C).

Teacher's Note:
a) Fluidity is shared by both the liquid and gaseous states of matter.
b) Solids have a rigid structure and fixed shape.

10. During summer, water kept in an earthen pot becomes cool because of the phenomenon of [1 Mark]
(A) diffusion
(B) transpiration
(C) osmosis
(D) evaporation

Answer: (D) evaporation

1. Earthen pots have tiny pores through which water seeps to the outer surface.
2. This water continuously evaporates, taking latent heat from the pot and remaining water.
3. Loss of heat causes cooling of the water inside.
4. Hence, the correct option is (D).

Teacher's Note:
a) Evaporation causes cooling due to absorption of latent heat of vaporization.
b) Porosity of earthen pots is essential for this cooling effect.

11. 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? [1 Mark]
(A) Water, air, wind
(B) Air, sugar, oil
(C) Oxygen, water, sugar
(D) Salt, juice, air

Answer: (C) Oxygen, water, sugar

1. Oxygen is a gas and has the weakest interparticle forces.
2. Water is a liquid with moderate interparticle forces.
3. Sugar is a solid with the strongest interparticle forces among the three.
4. Hence, the correct option is (C).

Teacher's Note:
a) Solid state has maximum force of attraction, gas has minimum, and liquid is intermediate.
b) Air and wind are essentially gases, making options with improper states incorrect.

12. On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of temperature will be [1 Mark]
(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: (A) 298 K, 311 K and 339 K

1. Temperature in Kelvin = Temperature in Celsius + 273.
2. 25°C = 25 + 273 = 298 K.
3. 38°C = 38 + 273 = 311 K and 66°C = 66 + 273 = 339 K.
4. Hence, the correct option is (A).

Teacher's Note:
a) Kelvin is the SI unit of temperature.
b) Always add 273 to Celsius temperature to convert it to Kelvin.

13. 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? [1 Mark]
(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

1. Diethyl ether: 35 + 273 = 308 K.
2. Acetone: 56 + 273 = 329 K.
3. n-butyl alcohol: 118 + 273 = 391 K.
4. Hence, the correct option is (C).

Teacher's Note:
a) Conversion relation is K = °C + 273.
b) Double-check addition for each liquid carefully.

14. Which condition out of the following will increase the evaporation of water? [1 Mark]
(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

1. Evaporation increases with an increase in temperature because kinetic energy of particles increases.
2. Decreasing temperature or surface area decreases evaporation rate.
3. Adding salt lowers vapor pressure, decreasing evaporation.
4. Hence, the correct option is (A).

Teacher's Note:
a) Surface area, temperature, humidity, and wind speed affect evaporation.
b) Higher temperature provides more energy for molecules to escape into the vapor phase.

15. Choose the correct statement of the following [1 Mark]
(a) conversion of solid into vapours without passing through the liquid state is called vapourisation.
(b) conversion of vapours into solid without passing through the liquid state is called sublimation.
(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: (b) conversion of vapours into solid without passing through the liquid state is called sublimation.

1. Sublimation is the transition of a substance directly from the solid to the gas state, or inversely from gas to solid, without passing through the liquid phase.
2. Vaporisation is the conversion of liquid into vapour.
3. Freezing is the conversion of liquid into solid.
4. Hence, the correct option is (b).

Teacher's Note:
a) Sublimation applies to both solid-to-gas and gas-to-solid transitions.
b) Always read definitions carefully to avoid confusing phase changes.

16. In which of the following conditions, the distance between the molecules of hydrogen gas would increase? [1 Mark]
(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
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

Answer: (c) (ii) and (iii)

1. Gas molecules occupy the entire available space inside a container.
2. When gas leaks out (ii), fewer molecules remain in the same volume, increasing the average distance between them.
3. Increasing the container volume (iii) allows molecules to spread out further, increasing inter-molecular distance.
4. Hence, the correct option is (c).

Teacher's Note:
a) Intermolecular distance in gases depends directly on volume and inversely on the amount of gas.
b) Pressure reduction or volume expansion increases particle separation.

17. A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following graph would correctly represent the result? Justify your choice. [2 Marks]

Answer:
1. Graph (d) correctly represents the process.
2. When a beaker containing ice and water is heated, the temperature remains constant at 0°C until all the ice melts completely due to latent heat of fusion. After that, the temperature of water rises steadily with time.

Teacher's Note:
a) Temperature does not change during a phase change.
b) Heat supplied is used entirely to overcome intermolecular forces during melting.

18. A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs would correctly represent the change in its temperature as a function of time. [2 Marks]

Answer:
1. Graph (a) correctly represents the change in temperature.
2. Hot water cools down to 0°C, remains at 0°C while freezing into ice (latent heat is released), and then the temperature of ice decreases below 0°C.

Teacher's Note:
a) Phase change from liquid to solid occurs at a constant freezing point temperature.
b) A flat region on a cooling curve indicates freezing or condensation.

19. 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. [2 Marks]

Answer:
1. The water is not pure because pure water boils at exactly 100°C at normal atmospheric pressure.
2. The presence of dissolved impurities raises the boiling point and lowers the freezing point, so this water will freeze at a temperature lower than 0°C.

Teacher's Note:
a) Boiling point elevation and freezing point depression are colligative properties caused by impurities.
b) Purity of liquids is tested using fixed melting and boiling points.

20. ‘Osmosis is a special kind of diffusion’. Comment. [2 Marks]

Answer:
1. Osmosis is similar to diffusion because solvent molecules move from a region of higher concentration to a region of lower concentration.
2. It is considered a special kind of diffusion because it involves the movement of solvent molecules across a semi-permeable membrane.

Teacher's Note:
a) Both processes represent passive transport driven by concentration gradients.
b) The mandatory presence of a semi-permeable membrane distinguishes osmosis from general diffusion.

21. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations. [2 Marks]

Answer:
1. Ice at 0°C absorbs latent heat of fusion (3.34 × 10⁵ J/kg) from the surroundings to melt, thereby providing a greater cooling effect than ice-cold water.
2. Steam at 100°C releases extra latent heat of vaporization (2.26 × 10⁶ J/kg) upon condensing into water, causing more severe burns than boiling water at the same temperature.

Teacher's Note:
a) Latent heat accounts for the severe energy transfer during phase changes.
b) Steam carries significantly more thermal energy per unit mass than boiling water.

22. Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment. [3 Marks]

Answer:
1. The temperature of both boiling water and steam is same, which is \(100^\circ\text{C}\) (or \(373\text{K}\)).
2. However, steam causes more severe burns than boiling water at the same temperature.
3. This is because steam has absorbed extra heat energy known as latent heat of vaporization during the phase change from liquid to gas.

Teacher's Note:
a) Focuses on latent heat of vaporization.
b) Students often incorrectly assume steam is hotter simply because it feels more intense.
c) Remind students that phase change temperatures remain constant until complete conversion.

23. Look at below figure and suggest in which of the vessels A,B, C or D the rate of evaporation will be the highest? Explain. [3 Marks]

Vessels A, B and C are open (C is directly under the moving fan); vessel D is covered with a lid.

Answer:
1. The rate of evaporation will be the highest in vessel C.
2. Evaporation is a surface phenomenon and increases with an increase in surface area.
3. Vessel C is open, has a large exposed surface area and is placed directly under the moving fan, so the air speed increases the rate of evaporation. Vessel D is covered with a lid, so evaporation from it is the lowest; vessels A and B are open but are not under the fan (B also has a smaller surface area).

Teacher's Note:
a) Relates surface area to the rate of evaporation.
b) Ensure students compare the dimensions of all four vessels visually from the diagram.
c) Highlight that wind speed and surface area both act as accelerating factors.

24. You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram. [5 Marks]

Answer:
1. Both ammonium chloride and naphthalene are sublimable solids, but this mixture cannot be separated by sublimation directly because both sublime on heating.
2. Take the mixture in a china dish and add water to it, then stir well.
3. Naphthalene is insoluble in water and floats, whereas ammonium chloride dissolves in water.
4. Filter the mixture using filter paper; naphthalene remains as residue on the filter paper and is washed and dried.
5. Evaporate the filtrate (aqueous ammonium chloride solution) to obtain solid ammonium chloride crystals.

Teacher's Note:
a) Tests application of separation techniques when standard sublimation fails for two sublimable components.
b) A common trap is suggesting direct sublimation without considering that both sublime.
c) Emphasize the difference in solubility of the two substances in water.

25. 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? [2 Marks]

Answer:
1. Priyanshi will be more comfortable because she is wearing cotton clothes.
2. Cotton is a good absorber of water, which helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation, producing a cooling effect.

Teacher's Note:
a) Explains the property of cotton in absorbing sweat.
b) Synthetic clothes like nylon do not absorb sweat easily, making the wearer uncomfortable in summer.

26. 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? [3 Marks]

Answer:
1. Spread the shirt out completely to increase the surface area for evaporation.
2. Hang it under a fan or in an open sunny area to increase wind speed and temperature.
3. Iron the damp shirt to use thermal energy for quick vaporization of remaining water.

Teacher's Note:
a) Covers factors affecting evaporation such as surface area, temperature, and wind speed.
b) Mentioning practical steps like ironing shows application of latent heat.

27. Comment: Evaporation produces cooling. [2 Marks]

Answer:
1. During evaporation, liquid particles absorb energy from the surroundings to compensate for the energy lost during the phase change.
2. This absorption of heat from the surrounding environment makes the surroundings cold, thus producing cooling.

Teacher's Note:
a) Focuses on energy absorption during liquid-to-gas transition.
b) Everyday examples include acetone on palms or sweating.

28. Comment: Rate of evaporation of an aqueous solution decreases with increase in humidity. [2 Marks]

Answer:
1. Humidity is the amount of water vapour present in the air.
2. When the air is already holding a high amount of water vapour, its capacity to take in more water vapour decreases, thereby reducing the rate of evaporation.

Teacher's Note:
a) Defines humidity and its inverse relationship with evaporation rate.
b) Students must mention air holding capacity clearly.

29. Comment: Sponge though compressible is a solid. [2 Marks]

Answer:
1. A sponge has minute holes in which air is trapped, making it compressible when pressed.
2. Despite this, it has a definite shape, fixed volume, and rigid structure when at rest, which are characteristic properties of a solid.

Teacher's Note:
a) Addresses the exception to rigidity in solids.
b) Emphasize the role of trapped air pockets.

30. Why does the temperature of a substance remain constant during its melting point or boiling point? [2 Marks]

Answer:
1. The heat supplied is continuously used up in overcoming the forces of attraction between the particles of the substance during change of state.
2. As this heat energy is used up as latent heat without increasing the kinetic energy of the particles, the temperature remains constant.

Teacher's Note:
a) Explains the concept of latent heat and constant temperature.
b) Clearly distinguish between kinetic energy and potential energy of particles during phase change.