Question Opening prompt 1
Why can stones or sand be piled up, but water cannot be piled up in the same way?
Steps only
Solids keep their shape; liquids flow and spread.
Answer
Stones and sand can form piles, but water flows away.
CLASS 8 · SCIENCE · CHAPTER 7
Particulate Nature of Matter
Simple answers to the opening prompts, all nine chapter activities, the temperature investigation, all ten end questions, reflection prompts, and four projects.
31 worked answersComplete chapter answers
31 worked answers · short steps first, explanations when you need them
Probe and Ponder
Textbook pages 98
Question Opening prompt 2
Why does water take the shape of folded hands but lose that shape when released?
Steps only
Water flows to fit its container or the space around it.
Answer
It takes the hand shape briefly, then flows away when released.
Question Opening prompt 3
We cannot see air. How does it add weight to an inflated balloon?
Steps only
Air has mass, and gravity pulls on it.
Answer
The air inside adds weight to the balloon.
Question Opening prompt 4
Is the air we breathe today the same air that existed thousands of years ago?
Steps only
Air is continually mixed and its particles move through natural cycles.
Answer
Some particles may be old, but the air is constantly changing and mixing.
Question Opening prompt 5
Share one question you have about particles of matter.
Steps only
Ask a clear question about particles, states, or dissolving.
Answer
Example: Where do sugar particles go when sugar dissolves?
Keep the Curiosity Alive
Textbook pages 113–115
Question 1
Choose the correct statement about the particles in solids and liquids: (i) They are close in solids but stationary in liquids. (ii) They are far apart in solids and fixed in liquids. (iii) They always move in solids but are fixed in liquids. (iv) They are close in solids and can move past one another in liquids.
Steps only
Compare how particles are arranged and move in each state.
Answer
(iv) Closely packed in solids; moving past one another in liquids.
Question 2
Mark each statement true or false and correct the false ones: (i) Melting ice changes a solid into a liquid. (ii) Melting weakens interparticle attractions. (iii) Solids have fixed shape and volume. (iv) Solid particles have strong attractions and very small spaces. (v) When heated, camphor fragrance reaches every corner of a room. (vi) Heating energy is released as a smell.
Steps only
Check state changes, particle spacing, and how vapour spreads.
Answer
- (i) T
- (ii) T
- (iii) T
- (iv) T
- (v) T
- (vi) F — camphor particles spread through air; energy is not a smell.
Question 3
If all the constituent particles were removed from a chair, what would happen? (i) Nothing changes (ii) It weighs less (iii) Nothing of the chair remains.
Steps only
The particles make up the chair itself.
Answer
(iii) Nothing of the chair remains.
Question 4
Why do gases mix easily, while solids do not?
Steps only
Gas particles move freely; solid particles are held in place.
Answer
Gases diffuse and mix easily, but solids stay in fixed arrangements.
Question 5
Spilled milk flows and spreads out, but a glass tumbler keeps its shape. Explain why.
Steps only
Liquid particles flow past one another; solid particles stay in place.
Answer
Milk spreads because it is liquid; the solid glass keeps its shape.
Question 6
Draw how particles are arranged as ice melts and changes into water vapour.
Steps only
Draw close fixed particles, then close mobile particles, then widely spaced particles.
Answer
Ice → water → vapour: fixed and close → mobile and close → far apart and free.
Question 7
Draw particle diagrams for (i) aluminium foil (ii) glycerin (iii) methane gas.
Steps only
Use the particle pattern for each material's state.
Answer
Aluminium: close and fixed; glycerin: close and mobile; methane: far apart and free.
Question 8
In the figure of a recently extinguished candle, identify the states of wax and match each state with its particle arrangement.
Steps only
Match the candle body, melted wax, and vapour to solid, liquid, and gas.
Answer
Candle body—solid; melted wax—liquid; wax vapour—gas.
Question 9
Why does ocean water taste salty even though the salt cannot be seen?
Steps only
Dissolved salt particles are present even though they cannot be seen.
Answer
The tiny dissolved salt particles make ocean water taste salty.
Question 10
Rice grains and rice flour take the shape of different jars. Are they solids or liquids? Explain.
Steps only
The pieces are solid even though a pile of them takes a container's shape.
Answer
Rice grains and rice flour are solids, not liquids.
Question Question-making activity
Prepare questions using prompts such as why, when, how long, where, and why not, based on the chapter.
Steps only
Turn ideas about particles and states into clear questions.
Answer
Answers vary; use the chapter's concepts to make questions.
Question Reflection activity
Reflect on the questions framed by your friends and try to answer them.
Steps only
Use the chapter's particle model to answer classmates' questions.
Answer
Answers vary; support each answer with a particle explanation.
Discover, Design, and Debate
Textbook pages 115
Question Project 1
Fit a balloon over a bottle neck and place the bottle in hot water. Predict and observe what happens.
Steps only
Warm air particles move faster and push the balloon outward.
Answer
The balloon expands as the air in the bottle warms.
Question Project 2
Make models of solid, liquid, and gas particles using clay balls, beads, or similar materials to show interparticle spacing.
Steps only
Show solids close and fixed, liquids close and mobile, and gases far apart.
Answer
Use beads or clay pieces to compare spacing and movement.
Question Project 3
Create a role-play or dance showing particles in solids, liquids, and gases at different temperatures.
Steps only
Act out how spacing and movement differ in each state.
Answer
Solids vibrate; liquids flow past; gases move freely. Heating speeds particles up.
Question Project 4
Debate whether the ability of gases to spread and fill all available space is beneficial or harmful.
Steps only
Give useful examples and risks of gases spreading.
Answer
Gas diffusion helps air and useful gases spread, but can also spread smoke or leaks.
Activities and Observations
Textbook pages 99–111
Question Activity 7.1
What do you observe when chalk is broken, ground to powder, and viewed with a magnifying glass? Has the chalk changed into a new substance?
Steps only
What do you observe when chalk is broken, ground to powder, and viewed with a magnifying glass? Has the chalk changed into a new substance?
Answer
The chalk breaks into smaller pieces and then into fine grains, but the grains are still chalk.
Question Activity 7.2
What does the activity show about sugar after it dissolves in water?
Steps only
What does the activity show about sugar after it dissolves in water?
Answer
After sugar dissolves, the water is sweet throughout even though we can no longer see sugar grains.
Question Activity 7.3
What do observing and gently testing different solid objects tell us about the particles in solids?
Steps only
What do observing and gently testing different solid objects tell us about the particles in solids?
Answer
Solids keep a definite shape and volume.
Question Activity 7.4
What happens to the shape and volume of the same 200 mL of water as it is poured through containers of different shapes?
Steps only
What happens to the shape and volume of the same 200 mL of water as it is poured through containers of different shapes?
Answer
The water takes the shape of each container, but its volume stays about 200 mL if none is spilled or left on the walls.
Question Activity 7.5
What happens when smoke trapped in one gas jar is allowed to spread into a second jar?
Steps only
What happens when smoke trapped in one gas jar is allowed to spread into a second jar?
Answer
The smoke spreads into the second jar and eventually fills the available space in both jars.
Question Activity 7.6
What happens when air is trapped in a syringe and its plunger is pushed? How does water compare?
Steps only
What happens when air is trapped in a syringe and its plunger is pushed? How does water compare?
Answer
The trapped air can be compressed: its volume becomes smaller because its particles have large spaces between them.
Question Activity 7.7
What happens to the water level when sugar is added and then dissolved? What happens with sand?
Steps only
What happens to the water level when sugar is added and then dissolved? What happens with sand?
Answer
The level rises when sugar is added, then falls somewhat after the sugar dissolves because sugar particles fit into spaces between water particles.
Question Activity 7.8
What happens when a grain of potassium permanganate is placed in water?
Steps only
What happens when a grain of potassium permanganate is placed in water?
Answer
Pink streaks spread from the grain, and over time the water becomes evenly pink.
Question Think like a scientist: hot, room-temperature, and cold water
In which water will potassium permanganate spread fastest: hot, room-temperature, or ice-cold water?
Steps only
In which water will potassium permanganate spread fastest: hot, room-temperature, or ice-cold water?
Answer
It spreads fastest in hot water, more slowly at room temperature, and slowest in ice-cold water.
Question Activity 7.9
What does smelling an incense fragrance some distance away after a short time show?
Steps only
What does smelling an incense fragrance some distance away after a short time show?
Answer
The fragrance particles spread through the air and reach us.