Class 8 Science · Chapter 7

7. Particulate Nature of Matter

Complete solutions to Keep the Curiosity Alive. CBSE / NCERT Class 8 Science (Curiosity).

Keep the Curiosity Alive

1The primary difference between solids and liquids is that the constituent particles are

Answer: (iv) closely packed in solids and move past each other in liquids.

2Which 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. — True

(ii) Melting process involves a decrease in interparticle attractions during the transformation. — True

(iii) Solids have a fixed shape and a fixed volume. — True

(iv) The interparticle interactions in solids are very strong, and the interparticle spaces are very small. — True

(v) When we heat camphor in one corner of a room, the fragrance reaches all corners of the room. — True

(vi) On heating, we are adding energy to the camphor, and the energy is released as a smell. — False

Correct statement: on heating, camphor particles gain energy and change into vapour. These camphor particles spread through the air and reach our nose. So we get the smell.

3If we could remove all the constituent particles from a chair, what would happen? Choose the correct answer with justification.

Answer: (iii) Nothing of the chair will remain.

Every object is made up of tiny particles. The chair is nothing but its particles held together. If all the particles are removed, no matter is left. So the chair will not remain at all.

4Why do gases mix easily, while solids do not?

In gases, interparticle attractions are negligible and interparticle spaces are maximum. The particles move freely. So particles of one gas easily move into the spaces between particles of another gas.

In solids, the particles are closely packed and held by strong attractions. They cannot move from their places. So solids do not mix on their own.

5When 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.

Milk is a liquid. Its particles are held by weaker attractions. They can move past each other. So milk flows and spreads out. A liquid has no fixed shape.

The tumbler is a solid. Its particles are closely packed with strong attractions and cannot move from their places. So it keeps its fixed shape.

6Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.

Ice → water → water vapour: the particles move farther apart and the attractions become weaker.

Ice: particles are closely packed in fixed positions.
Water: particles are slightly farther apart and can move past each other.
Water vapour: particles are very far apart and move freely in all directions.

7Draw a picture representing particles present in (i) Aluminium foil (ii) Glycerin (iii) Methane gas.

Arrangement of particles in a solid, a liquid and a gas.

Aluminium foil is a solid, glycerin is a liquid and methane is a gas.

8Fig. 7.16a shows a candle that was just extinguished after burning for some time. Identify the different states of wax and match them with Fig. 7.16b.

Solid wax — the body of the candle. It matches the box with closely packed particles.
Liquid wax — the melted wax near the wick and the drips on the sides. It matches the box with close but irregular particles.
Wax vapour (gas) — the white fumes rising from the wick. It matches the box with few, far-apart particles.

9Why does the water in the ocean taste salty, even though the salt is not visible? Explain.

Salt dissolves in water. Its particles get into the spaces between the water particles. They spread evenly throughout the water.

The salt particles are extremely small, so we cannot see them. But they are still present. So the water tastes salty.

10Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.

They are solids.

Each grain of rice or particle of flour has its own fixed shape and volume. It does not flow on its own like a liquid. They take the shape of the jar only because they are small separate pieces that settle into the empty spaces.

Discover, Design, and Debate

The “Discover, design, and debate” projects are hands-on tasks. Do them with your classmates under the guidance of your teacher, and write your own observations.

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