Particulate Nature of Matter Class 8 Question Answer Science Chapter 7

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Class 8 Science Curiosity Chapter 7 Question Answer

Class 8 Science Ch 7 Particulate Nature of Matter Question Answer

Class 8 Science Chapter 7 Particulate Nature of Matter Question Answer (InText)

Question 1.
Why is it possible to pile up stones or sand, but not a liquid like water? (Page 98)
Answer:
Stones and sand are solids. Their particles are tightly packed and stay in one place, so they can be piled up. Water is a liquid, and its particles can move freely, so it flows and cannot be piled.

Question 2.
Why does water take the shape of folded hands but lose that shape when released? (Page 98)
Answer:
Water is a liquid, and liquids do not have a fixed shape. They take the shape of the container they are poured into. When water is poured into folded hands, it adjusts to that shape. But, as soon as the hands are opened, water flows out and takes the shape of the new surface because particles of a liquid can move freely.

Question 3.
We cannot see air, so how does it add weight to an inflated balloon? (Page 98)
Answer:
Air is made of tiny particles. When a balloon is inflated, air particles get trapped inside and occupy space. These particles add weight to the balloon even though they are not visible.

Question 4.
Is the air we breathe today the same that existed thousands of years ago? (Page 98)
Answer:
Yes, air is made of particles that keep moving and mixing. The same air particles are reused in nature over time, so the air today is mostly the same as it was thousands of years ago.

Question 5.
Is every speck of the fine chalk powder still composed of the same substance, or has it changed into something else on breaking or grinding? (Page 99)
Answer:
It is still the same chalk. Grinding only breaks it into smaller particles without changing its substance. It is a physical change.

Question 6.
Are the units of chalk obtained in breaking or grinding considered as the smallest units of chalk? (Page 99)
Answer:
No. These can be broken further into smaller particles called constituent particles, which are the building blocks of chalk.

Question 7.
What do you observe when sugar is added to water and stirred? (Page 100)
Answer:
Sugar disappears from sight, but the water becomes sweet. This shows that sugar breaks into tiny particles that occupy spaces between water particles.

Question 8.
Why does sugar disappear when dissolved in water, but its taste remains? (Page 100)
Answer:
Sugar breaks down into particles too small to be seen, but they remain present and make the solution taste sweet.

Question 9.
Chalk and sugar can both be broken down into their constituent particles. But how are the constituent particles held together to form the solid pieces we see? (Page 101)
Answer:
The constituent particles in solids like chalk and sugar are held together by interparticle forces of attraction. These forces pull the particles tightly together, keeping them in fixed positions and giving solids a definite shape and volume.

Question 10.
In the solid state, is there any way to move these particles apart? (Page 102)
Answer:
It is done only by heating. Heating makes the particles vibrate more vigorously and weakens their attraction, causing the solid to melt into a liquid.

Question 11.
Solids have a definite volume; what about liquids and gases? (Page 103)
Answer:
Liquids also have a definite volume but no fixed shape—they can take the shape of the container in which they are kept in. Gases have neither a fixed shape nor a definite volume—they spread out to fill the entire space available.

Question 12.
Why does water take the shape of a container but maintain its volume? (Page 104)
Answer:
Water particles move freely and adjust their positions to take the shape of the container, but their total quantity (volume) remains unchanged.

Question 13.
Do gases also have a fixed volume? (Page 105)
Answer:
No, gases do not have a fixed volume. Their particles are far apart and move freely in all directions, so gases expand to fill the entire space of the container they are in.

Question 14.
What role does the interparticle spacing play in determining the properties of each state (solid, liquid, and gas)? (Page 107)
Answer:
Interparticle spacing affects the strength of interparticle attractions. In solids, particles are closely packed, so attractions are strong and solids have fixed shape and volume. In liquids, particles are a little farther apart, so attractions are weaker, allowing them to flow but keep their volume. In gases, particles are far apart, attractions are negligible, and gases have neither fixed shape nor volume.

Question 15.
Sugar and sand are both solids. Why does sugar dissolve in water but sand does not? (Page 108)
Answer:
Sugar particles are small enough to fit into the spaces between water particles. Sand particles are bigger and do not dissolve.

Question 16.
What do you think about the interparticle spacing in solids?
Answer:
In solids, the interparticle spacing is very small because the particles are closely packed.
There is almost no space between them, and they are held together by strong forces of attraction.

Question 17.
What happens when potassium permanganate is dropped into water? (Page no)
Answer:
It dissolves and spreads slowly in water. This happens because water particles are in constant motion and help distribute the colour.

Question 18.
How can we demonstrate the movement of gas particles that cannot be seen with the naked eye?
(Page 110)
Answer:
We can light an incense stick in one corner of a room. After some time, its fragrance spreads throughout the room. This shows that gas particles are in constant motion and help spread the fragrance, even though they cannot be seen.

Particulate Nature of Matter Class 8 Questions and Answers (Exercise)

Question 1.
Choose the correct option.
The primary difference between solids and liquids is that the constituent particles are:
(i) closely packed in solids, while they are stationary liquids.
(ii) far apart in solids and have fixed position in liquids.
(iii) always moving in solids and have fixed position liquids.
(iv) closely packed in solids and move past each other in liquids.
Answer:
(iv) The primary difference between solids and liquids is that the constituent particles are closely packed in solids and move past each other in liquids.

Question 2.
Which of the following statements are true? Correct the false statements.
(i) Melting ice into water is an example of the transformation of a solid into a liquid.
(ii) Melting process involves a decrease in interparticle attractions during the transformation.
(iii) Solids have a fixed shape and a fixed volume.
(iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small.
(v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room.
(vi) On heating, we are adding energy to the camphor, and the energy is released as a smell.
Answer:
(i) True
(ii) True
(iii) True
(iv) True
(v) True
(vi) False. This statement can be corrected as, on heating camphor, we add energy which helps its particles overcome intermolecular forces and change directly from solid to gas. The smell is due to gaseous camphor particles spreading in air through diffusion, not energy being “released as smell”.

Question 3.
Choose the correct answer with justification. If we could remove all the constituent particles from a chair, what would happen?
(i) Nothing will change.
(ii) The chair will weigh less due to lost particles.
(iii) Nothing of the chair will remain.
Answer:
(iii) According to the chapter Particulate Nature of Matter, everything around us is made of matter, and all matter is composed of extremely small constituent particles. If these particles are completely removed, there will be no matter left. Therefore, if all the constituent particles are removed from a chair, the chair itself will cease to exist and nothing of the chair will remain.

Question 4.
Why do gases mix easily, while solids do not?
Answer:
Gases mix easily because the particles in gases are far apart and move freely in all directions. These particles have negligible interparticle attraction, allowing them to spread and combine rapidly. In contrast, solids have tightly packed particles held together by strong interparticle forces. The particles in solids cannot move from their fixed positions, which is why solids do not mix easily.

Question 5.
When spilled on the table, milk in a glass tumbler flows and spreads out, but the glass tumbler stays in the same shape. Justify this statement.
Answer:
Milk is a liquid. Its particles are loosely packed and have the freedom to move past one another, which allows it to flow and take the shape of any container or spread on a surface. On the other hand, the glass tumbler is a solid. Its particles are tightly packed and held together by strong interparticle forces, so it retains a definite shape and does not flow. This difference in particle arrangement and movement explains the observed behaviour.

Question 6.
Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
Answer:
The transformation of ice (solid) to water (liquid) and then to water vapour (gas) involves a gradual increase in the spacing and movement of particles. The diagrams below represent the particle arrangement in each state.

These changes occur due to increased thermal energy, which weakens the interparticle attractions and allows more freedom of movement.

Question 7.
Draw a picture representing particles present in the following:
(i) Aluminium foil
(ii) Glycerin
(iii) Methane gas
Answer:
(i) Aluminium foil (Solid) Particles are tightly packed in a regular and fixed arrangement.

(ii) Glycerin (Liquid) Particles are loosely packed and move around one another.

(iii) Methane gas (Gas) Particles are far apart and move freely in all directions.

Question 8.
Observe Fig. (a) which shows the image of a candle that was just extinguished after burning for some time. Identify the different states of wax in the figure and match them with Fig.(b) showing the arrangement of particles.

Answer:
In the image of the extinguished candle:

• The solid wax is the remaining portion of the candle that retains its shape. It corresponds to particles that are closely packed in an orderly arrangement as shown in the solid-state diagram (Fig. (b)).

• The liquid wax is the molten wax near the wick just after the flame goes out. It corresponds to particles that are loosely packed and able to move around, matching the arrangement in the liquid-state diagram.

• The wax vapour or smoke seen rising above the candle represents the gaseous state. It corresponds to particles that are far apart and moving freely, as shown in the gas-state diagram in Fig. (b).

Each of these states of wax is distinguished by the spacing and movement of its particles, reflecting the change in physical state due to heating.

Question 9.
Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
Answer:
When salt dissolves in ocean water, it breaks down into tiny particles that occupy the spaces between water particles. These dissolved salt particles are too small to be seen with the naked eye, but they remain present and can be tasted. This is why ocean water tastes salty even though the salt is not visible.

Question 10.
Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
Answer:
Grains of rice and rice flour are solids. Although they appear to take the shape of the container, each grain or particle retains its own definite shape. They behave like solids because their particles do not flow freely like those in liquids. The overall shape seems to change only because the individual solid particles shift and settle within the container.

Class 8 Science Chapter 7 Question Answer (Activities)

Activity 1 (Page 99)

Aim
To understand that matter is made up of extremely small particles by breaking and grinding a chalk stick.

Materials Required
A stick of chalk, a mortar and pestle and a magnifying glass.

Procedure

1. Take a full stick of chalk and break it into two pieces.
2. Continue breaking the pieces further until you cannot break them easily by hand.
3. Put the smaller pieces into a mortar and crush them using a pestle to obtain fine chalk powder.
4. Observe the powder carefully using a magnifying glass.
5. Try to understand whether the smallest specks still look like chalk or something else.

Observation Table

Step performed	Observation
Chalk broken into smaller pieces	Each piece still looks like chalk
Grinding into fine powder	Particles are very tiny but still chalk
Observation under magnifying glass	Fine grains appear as small chalk specks

Conclusion
We conclude that even the smallest grains obtained from grinding chalk still look like chalk. This means that chalk is made up of very tiny particles called constituent particles, which retain the properties of chalk. Grinding only reduces the size of the chalk but does not change its substance. This is a physical change.

Viva Questions

1. What happens to chalk when we grind it into fine powder?
2. What do we call the smallest units that make up chalk?
3. Is grinding chalk a physical or a chemical change? Why?

Activity 2 (Page 100)

Aim
To observe what happens to sugar when it dissolves in water and understand that matter is made up of extremely small particles.

Materials Required
A glass tumbler, drinking water, two teaspoons of sugar and a spoon.

Procedure

1. Fill a glass tumbler with drinking water.
2. Add two teaspoons of sugar to the water without stirring.
3. Taste a small spoonful of water from the top layer and note whether it tastes sweet.
4. Now stir the water until the sugar completely dissolves.
5. Again, taste a spoonful of water from the top layer and compare the taste.
6. Observe whether any sugar particles are visible in the solution.

Observation Table

Step Performed	Observation
Sugar added without stirring	Water at the top does not taste very sweet
Water stirred	Sugar dissolves completely; particles not visible
Water tasted after stirring	Water tastes sweet, indicating sugar is still present

Conclusion
We conclude that the sugar particles, though not visible but they are still present in the solution and can be sensed by taste. This shows that sugar breaks down into extremely small constituent particles which occupy the spaces between water particles. This activity confirms that matter is made up of tiny particles and that there is space between them.

Viva Questions

1. What happens when sugar is stirred in water?
2. Why does the water taste sweet after dissolving sugar?
3. Can you see sugar in the water after stirring? Why or why not?

Activity 3 (Page 102)

Aim
To observe the physical properties of various solids and understand that solids have tightly packed particles with strong interparticle attractions.

Materials Required
A piece of iron or iron nail, a piece of rock salt, a stone, a piece of wood, a metal key and a piece of
aluminium.

Procedure

1. Collect samples of the given solid objects.
2. Observe the shape and size of each object.
3. Gently hammer each object on a hard surface.
4. Note whether the object flattens, breaks, or resists hammering.
5. Try to infer which objects have particles that are held together more strongly.

Observation Table

Object/Material	Shape & Size	Effect of Hammering	Inference on Particle Arrangement
Iron nail	Hard, metallic, fixed shape	Resists or flattens	Particles are tightly packed
Rock salt	Crystalline, fixed shape	Breaks into small pieces	Particles are held tightly but brittle
Stone	Irregular, hard	May chip or break	Strongly held particles
Wood	Fixed shape, rough texture	May dent or crack	Tightly held particles but less than metals
Key	Metallic, definite shape	Resists hammering	Very strong particles attraction
Aluminium piece	Smooth, metallic	Flattens slightly	Strongly held particles

Conclusion
We conclude that all the materials observed in this activity are solids. They have a fixed shape and volume due to tightly packed particles held together by strong interparticle forces.

The resistance to hammering or their manner of breaking indicates how strongly the particles are bound. Solids only allow slight vibration of their particles but do not permit them to move freely.

Viva Questions

1. What property of solids gives them a definite shape?
2. What happens to solid particles when we apply force, such as hammering?
3. Which material among those used showed the strongest resistance to hammering?

Activity 4 (Page 104)

Aim
To observe that liquids take the shape of the container but retain a fixed volume.

Materials Required
Three clean and dry containers of different shapes, drinking water, marker or paper strips for marking, and a measuring beaker or jug.

Procedure

1. Take three containers of different shapes and label them A, B and C.
2. Mark the 200 mL level in each container using a marker or by sticking a paper strip.
3. Fill container A with water up to the 200 mL mark.
4. Carefully pour the water from container A into container B without spilling. Observe the shape and water level.
5. Now transfer the same water from container B to container C. Again, observe the shape and water level.
6. Try moving your finger through the water in a shallow dish and observe what happens.

Observation Table

Container Used	Shape of Water Surface	Water level	Inference
A	Matches container A	200 mL	Takes container’s shape
B	Matches container B	200 mL	No change in volume
C	Matches container C	200 mL	Volume remains constant
Water in a dish	Finger moves through it	200 mL	Water displaces and settles

Conclusion
We conclude that liquids do not have a fixed shape but have a definite volume. They take the shape of the container they are poured into due to the free movement of their particles. However, their volume remains unchanged. Liquids also offer little resistance to movement, as demonstrated when a finger passes through water without breaking it.

Viva Questions

1. What happens to the shape of water when it is poured into a differently shaped containers?
2. Does the amount of water change when poured from one container to another?
3. Why can a finger move easily through water but not through a solid?

Activity 5 (Page 105)

Aim
To demonstrate that gases do not have a fixed shape or volume and can spread to fill the entire available space.

Materials Required
Two transparent gas jars or glass tumblers, an incense stick, a glass plate and a matchbox.

Procedure

1. Label the two gas jars as A and B.
2. Light an incense stick to produce smoke.
3. Invert gas jar A over the burning incense stick to collect the smoke inside the jar.
4. Cover the mouth of jar A with a glass plate to trap the smoke.
5. Take Jar B, also inverted, and place it gently over the glass plate covering jar A.
6. Carefully remove the glass plate, ensuring that there is no gap between the jars.
7. Observe the movement of smoke from jar A to jar B.

Observation Table

Observation	Inference
Smoke remains inside Jar A	Gas is trapped in the container
After removing the glass plate, smoke spreads into Jar B	Gases can flow and spread to available space
Smoke fills the entire space of both jars	Gas occupies all available space
No fixed shape or volume observed	Gas particles move freely in all directions

Conclusion
We conclude that the gases do not have a definite shape or volume. The smoke, which represents gas particles, moves freely and spreads out to fill the entire space of both jars. This proves that gas particles are in constant motion and have negligible interparticle attraction. Gases, like liquids, flow and are classified as fluids.

Viva Questions

1. What did the smoke represent in this activity?
2. What happened when the glass plate was removed between the two jars?
3. What does this activity tell us about the shape and volume of gases?

Activity 6 (Page 107)

Aim
To understand the compressibility of gases and compare it with the incompressibility of liquids by using a syringe.

Materials Required
A syringe without a needle and a beaker of water.

Procedure

1. Pull the plunger of the syringe outward to its maximum to fill it with air.
2. Place your thumb tightly on the open end of the syringe to seal it.
3. Now, push the plunger inward slowly and steadily.
4. Observe what happens to the air inside the syringe.
5. Repeat the same steps with the syringe filled with water instead of air and observe.

Observation Table

Substance in Syringe	Observation on Pressing Plunger	Inference
Air (gas)	Plunger moves inward easily	Air is compressible due to large interparticle spaces.
Water (liquid)	Plunger resists movement	Water is nearly incompressible due to minimal interparticle spaces.

Conclusion
We conclude that the gases have large interparticle spaces which allow them to be compressed easily by applying pressure. In contrast, liquids have very little space between their particles and are nearly incompressible. Thus, the interparticle spacing plays a key role in determining the compressibility of different states of matter.

Viva Questions

1. What happens to the air inside the syringe when the plunger is pushed?
2. Why is it difficult to compress water in the syringe?
3. What does this activity reveal about the spacing between gas particles?

Activity 7 (Page 108)

Aim
To observe whether particles of a substance occupy spaces between water particles when dissolved and to understand interparticle spacing in different substances.

Materials Required
A glass vessel, drinking water, two teaspoons of sugar, a glass rod and a marker or tape for marking water levels.

Procedure

1. Fill the glass vessel about halfway with water and mark this initial level as A.
2. Add two teaspoons of sugar into the water and observe the rise in water level. Mark this as B.
3. Stir the solution thoroughly using a glass rod until all the sugar dissolves.
4. Observe the new level of water after the sugar has fully dissolved. Mark this as C.
5. Compare the levels A, B, and C to note any changes.
6. Repeat the activity with other substances like salt (soluble) and sand (insoluble).
   Observe if the water level changes and if the substances dissolve.

Observation Table

Substance added	Initial level (A)	Level after adding (B)	After stirring (C)	Substance Dissolved?	Observation
Sugar	A	B (increased)	C (Slightly lower)	Yes	Sugar dissolved and occupied spaces
Salt	A	B (increased)	C (slightly lower)	Yes	Salt also dissolved like sugar
Sand	A	B (increased)	C = B (no change)	No	Sand did not dissolve and settled at base.

Conclusion
We conclude that when sugar or salt is added to water, they dissolve and occupy the empty spaces between water particles. This results in a slight decrease in water level after stirring. However, insoluble substances like sand do not dissolve and only settle at the bottom, causing an overall increase in volume. This proves that liquids have interparticle spaces and that these spaces can be filled by dissolved substances.

Viva Questions

1. Why did the water level decrease after sugar dissolved in it?
2. What happened when sand was added to water?
3. What does this activity reveal about the structure of liquids?

Activity 8 (Page 109)

Aim
To observe how particles move in a liquid and understand the concept of particle motion and diffusion.

Materials Required
A glass tumbler filled with water, a few grains of potassium permanganate and a spoon or spatula.

Procedure

1. Take a clean glass tumbler and fill it with water.
2. Carefully add a few grains of potassium permanganate into the water using a spoon or spatula.
3. Do not stir the solution. Observe the colour changes over time.
4. Note how the pink colour from the potassium permanganate spreads through the water without stirring.
5. Record the time taken for the colour to become uniform.

Observation Table

Time After Adding Potassium Permanganate	Observation
Immediately	Pink streaks start to spread
After a few minutes	Colour spreads without stirring
After some time	Entire water becomes uniformly pink

Conclusion
We conclude that particles of water are constantly in motion. They pull out particles of potassium permanganate from the solid grains and help distribute them evenly throughout the liquid.

The spreading of colour without stirring proves that the particles in liquids move and collide with other particles. This movement is responsible for diffusion in liquids.

Viva Questions

1. Why does the pink colour spread in water even without stirring?
2. What does the uniform colour of the solution indicate?
3. Would sand show a similar result in this activity? Why or why not?

Activity 9 (Page 110)

Aim
To observe the movement of gas particles by detecting the spread of fragrance from a burning incense stick.

Materials Required
An incense stick, a matchbox or lighterand a well-ventilated room.

Procedure

1. Light an incense stick and place it in one corner of the room.
2. Stand at a distance and wait for a few minutes.
3. Observe when and how the fragrance reaches you.
4. Try to understand how the smell spreads from one point to the entire room.

Observation Table

Time After Lighting	Position in Room	Observation
Immediately	Near incense stick	Fragrance is strong and easily noticeable
After 2 – 3 minutes	A few steps away	Smell begins to reach this point
After some more time	Opposite corner	Fragrance spreads to entire room

Conclusion
We conclude that gases, like the fragrance from an incense stick, can spread through air. This spreading occurs because air particles are always in motion. They collide with the particles of the fragrance and help carry them throughout the room. This confirms that gas particles move freely and constantly in all directions.

Viva Questions

1. Why does the fragrance of an incense stick reach all corners of the room?
2. What does this activity prove about the nature of gases?
3. Can you think of a similar situation in real life where gas particles spread?