Case Study 1: Ice in a Glass
Ravi left some ice cubes in a glass on the table during summer. After 10 minutes, the ice completely melted into water. His sister noticed droplets forming on the outside of the glass.
Questions:
- The melting of ice is a change from:
(a) liquid → solid
(b) solid → liquid
(c) liquid → gas
(d) gas → liquid
Answer: (b) - Temperature at which ice melts = ?
(a) 0°C (b) 4°C (c) 100°C (d) –4°C
Answer: (a) - Droplets on the outside of the glass are due to:
(a) freezing (b) condensation (c) sublimation (d) evaporation
Answer: (b) - Which property of matter explains this?
(a) Kinetic energy (b) Intermolecular space (c) Intermolecular force (d) All of these
Answer: (d) - This is an example of:
(a) physical change (b) chemical change (c) irreversible change (d) combustion
Answer: (a)
Case Study 2: Diffusion of Perfume
Ananya sprayed perfume in one corner of her room. After a few minutes, her brother sitting at the other end of the room could smell it.
Questions:
- The process involved is:
(a) Osmosis (b) Evaporation (c) Diffusion (d) Condensation
Answer: (c) - Diffusion occurs because of:
(a) Kinetic energy of particles (b) Intermolecular space (c) Both (a) and (b) (d) None
Answer: (c) - Rate of diffusion increases with:
(a) increase in temperature (b) decrease in temperature (c) no change (d) solid state
Answer: (a) - Diffusion is fastest in:
(a) solids (b) liquids (c) gases (d) plasma
Answer: (c) - This activity proves that:
(a) Matter is continuous (b) Matter is particulate and dynamic (c) Matter is stationary (d) None
Answer: (b)
Case Study 3: Boiling of Water
Shreya boiled water in a vessel at home. After some time, bubbles formed and steam was visible.
Questions:
- Boiling point of pure water is:
(a) 0°C (b) 50°C (c) 100°C (d) 212°C
Answer: (c) - Boiling is a:
(a) surface phenomenon (b) bulk phenomenon (c) chemical reaction (d) condensation process
Answer: (b) - Latent heat of vaporization of water = ?
(a) 22.5 × 10⁵ J/kg (b) 2.25 × 10⁶ J/kg (c) 2.25 × 10⁵ J/kg (d) none
Answer: (b) - Change of water to steam is:
(a) physical change (b) chemical change (c) irreversible (d) combustion
Answer: (a) - Kinetic energy of particles at boiling point:
(a) decreases (b) increases (c) remains zero (d) constant
Answer: (b)
Case Study 4: Evaporation from Clothes
Rohit washed his clothes and spread them on a rope to dry. After a few hours, the clothes became dry.
Questions:
- Evaporation is a:
(a) surface phenomenon (b) bulk phenomenon (c) chemical change (d) irreversible process
Answer: (a) - Evaporation increases when:
(a) temperature increases (b) wind speed increases (c) humidity decreases (d) all of these
Answer: (d) - Cooling effect of evaporation is felt when:
(a) we sweat (b) water evaporates (c) alcohol evaporates (d) all of these
Answer: (d) - Which factor decreases rate of evaporation?
(a) high temperature (b) low humidity (c) high humidity (d) wind speed
Answer: (c) - The process involved in drying clothes:
(a) condensation (b) evaporation (c) sublimation (d) freezing
Answer: (b)
Case Study 5: Camphor on a Plate
Sneha placed some camphor (kapoor) on a plate. After some time, it disappeared without leaving liquid behind.
Questions:
- The process involved is:
(a) melting (b) evaporation (c) sublimation (d) condensation
Answer: (c) - Sublimation is:
(a) solid → liquid (b) solid → gas directly (c) gas → liquid (d) liquid → gas
Answer: (b) - Camphor and dry ice show:
(a) condensation (b) sublimation (c) evaporation (d) melting
Answer: (b) - This process is a:
(a) physical change (b) chemical change (c) both (d) none
Answer: (a) - Sublimation proves that matter:
(a) has no intermolecular force (b) can directly change state (c) is continuous (d) none
Answer: (b)
Case Study 6: LPG Cylinder
At home, an LPG cylinder is used for cooking. Inside the cylinder, the gas is stored in liquid form, but when the knob is opened it comes out as gas.
Questions:
- LPG inside the cylinder is in:
(a) solid state (b) liquid state (c) gaseous state (d) plasma
Answer: (b) - When knob is opened, liquid changes to:
(a) solid (b) gas (c) liquid (d) none
Answer: (b) - Which property allows this?
(a) High pressure liquefaction of gases (b) Diffusion (c) Evaporation (d) None
Answer: (a) - This is an example of:
(a) physical change (b) chemical change (c) irreversible change (d) sublimation
Answer: (a) - Energy supplied for change in state is used to:
(a) increase temperature (b) overcome intermolecular force (c) decrease temperature (d) none
Answer: (b)
Case Study 7: Steam Burns
Meena accidentally touched steam coming out of a boiling kettle and felt a severe burn.
Questions:
- Steam at 100°C causes more burn than boiling water at 100°C because:
(a) higher temperature (b) latent heat of vaporization (c) pressure (d) none
Answer: (b) - Latent heat is the heat:
(a) used to raise temperature (b) absorbed during change of state without rise in temperature (c) lost during cooling (d) none
Answer: (b) - Change of steam to water = ?
(a) evaporation (b) condensation (c) sublimation (d) freezing
Answer: (b) - Steam to water is:
(a) exothermic (b) endothermic (c) chemical change (d) none
Answer: (a) - Unit of latent heat = ?
(a) J (b) J/kg (c) cal (d) none
Answer: (b)
Case Study 8: Solid CO₂ (Dry Ice)
Dry ice is used in parties to create foggy effects. It changes directly into gas at room temperature.
Questions:
- Dry ice is:
(a) solid O₂ (b) solid CO₂ (c) liquid N₂ (d) none
Answer: (b) - Change of dry ice:
(a) solid → liquid (b) solid → gas (c) gas → liquid (d) liquid → solid
Answer: (b) - Process is called:
(a) evaporation (b) sublimation (c) condensation (d) deposition
Answer: (b) - Dry ice is used in:
(a) cold drinks (b) artificial fog (c) refrigeration (d) all
Answer: (d) - Dry ice sublimes at:
(a) –78°C (b) 0°C (c) –273°C (d) none
Answer: (a)
Case Study 9: Pressure Cooker
Cooking in a pressure cooker is faster than open vessel cooking because boiling point of water increases under pressure.
Questions:
- In pressure cooker, water boils at:
(a) less than 100°C (b) exactly 100°C (c) more than 100°C (d) 0°C
Answer: (c) - Increase in boiling point is due to:
(a) decreased pressure (b) increased pressure (c) no change (d) none
Answer: (b) - This principle is used in:
(a) cooking (b) autoclave sterilization (c) distillation (d) all
Answer: (d) - Faster cooking is due to:
(a) low pressure (b) high temperature (c) less water (d) less heat
Answer: (b) - Boiling point depends on:
(a) temperature (b) pressure (c) both (d) none
Answer: (c)
Case Study 10: Evaporation of Petrol
Arjun left a bowl of petrol open in the garage. After some time, he noticed that petrol had disappeared into the air.
Questions:
- Process here is:
(a) sublimation (b) evaporation (c) condensation (d) freezing
Answer: (b) - Volatile liquids evaporate:
(a) slowly (b) very fast (c) only at high temp (d) never
Answer: (b) - Petrol evaporation shows:
(a) intermolecular forces are weak (b) particles have high kinetic energy (c) both (d) none
Answer: (c) - Evaporation of petrol is:
(a) physical change (b) chemical change (c) irreversible (d) none
Answer: (a) - Which liquid evaporates faster?
(a) water (b) petrol (c) oil (d) honey
Answer: (b)