✅ Case Study 1: Evaporation and Its Daily Applications
Passage:
Rahul spilled a small amount of perfume on his hand while getting ready for school. He noticed a cool sensation on his skin. Later, he helped his mother spread wet clothes on the terrace to dry. After a while, the clothes dried up, despite it being a windy but cloudy day.
Questions:
- What caused Rahul to feel cool when perfume spilled on his hand?
a) Heat was released
b) Heat was absorbed due to evaporation
c) Friction
d) Condensation
✅ Answer: b) Heat was absorbed due to evaporation - Which factor was most responsible for quick drying of clothes in a windy condition?
a) High humidity
b) Low temperature
c) Increased surface area
d) Fast-moving air
✅ Answer: d) Fast-moving air - Which property of matter explains the spreading of perfume?
a) Compression
b) Rigidity
c) Diffusion
d) Expansion
✅ Answer: c) Diffusion - Evaporation causes cooling because:
a) Molecules lose energy
b) Heat is released
c) High energy molecules leave the surface
d) Condensation occurs
✅ Answer: c) High energy molecules leave the surface
✅ Case Study 2: States of Matter and Their Properties
Passage:
During a science class demonstration, the teacher heated camphor in a dish. Students observed that it changed directly into vapour without becoming liquid. Later, they placed an ice cube on a hot pan and saw water vapour rise immediately.
Questions:
- What process is observed when camphor turns into vapour directly?
a) Melting
b) Boiling
c) Condensation
d) Sublimation
✅ Answer: d) Sublimation - Ice melting on a hot pan and producing vapour immediately involves:
a) Melting and evaporation
b) Freezing
c) Condensation
d) Sublimation
✅ Answer: a) Melting and evaporation - What property of solids is best shown by camphor’s behaviour?
a) Definite volume
b) Ability to compress
c) Change of state
d) Surface tension
✅ Answer: c) Change of state - Which of the following substances shows sublimation like camphor?
a) Iron
b) Naphthalene
c) Water
d) Milk
✅ Answer: b) Naphthalene
✅ Case Study 3: Latent Heat and Temperature
Passage:
In an experiment, a student heats ice to convert it into water and further to steam. He notices that even though heat is continuously supplied, the temperature remains constant at 0°C during melting and 100°C during boiling.
Questions:
- The constant temperature at 0°C during melting is due to:
a) Heat loss
b) Evaporation
c) Latent heat of fusion
d) Diffusion
✅ Answer: c) Latent heat of fusion - The temperature remains constant at 100°C during:
a) Condensation
b) Freezing
c) Evaporation
d) Boiling
✅ Answer: d) Boiling - What is latent heat?
a) Heat that changes temperature
b) Heat that increases volume
c) Heat absorbed or released without change in temperature
d) None of the above
✅ Answer: c) Heat absorbed or released without change in temperature - The energy used during phase change:
a) Raises temperature
b) Breaks intermolecular forces
c) Creates new atoms
d) Cools the substance
✅ Answer: b) Breaks intermolecular forces
✅ Case Study 4: Diffusion and Gas Behavior
Passage:
An experiment was conducted by placing a few drops of ammonia solution in one corner of a room and hydrochloric acid in the opposite corner. A white ring formed in the middle after some time, due to a chemical reaction between the two gases.
Questions:
- What is the reason behind the white ring forming in the middle?
a) Both liquids spilled
b) Ammonia gas diffused faster
c) Gases met and reacted
d) Water evaporated
✅ Answer: c) Gases met and reacted - Which property allowed the gases to mix?
a) Rigidity
b) Evaporation
c) Diffusion
d) Surface tension
✅ Answer: c) Diffusion - The faster moving gas in the experiment is:
a) HCl
b) Ammonia
c) Oxygen
d) Carbon dioxide
✅ Answer: b) Ammonia - Why did the ring not form exactly in the center?
a) Ammonia is heavier
b) Ammonia diffuses faster than HCl
c) HCl reacted first
d) Ring always forms randomly
✅ Answer: b) Ammonia diffuses faster than HCl