Particulate Nature of MatterClass 8 Science NCERT Solutions
10 Solutions
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Solution 1 of 10
Q1Keep the curiosity alive
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 in liquids.
(ii)
far apart in solids and have fixed position in liquids.
(iii)
always moving in solids and have fixed position in liquids.
(iv)
closely packed in solids and move past each other in liquids.
Solution
The correct option is (iv) closely packed in solids and move past each other in liquids. In solids, the constituent particles are tightly packed due to strong interparticle attractions, restricting their movement. In liquids, the particles are still close together but have weaker interparticle attractions, allowing them to move past each other.
Q2Keep the curiosity alive
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.
Solution
(i)
True
(ii)
True
(iii)
True
(iv)
True
(v)
True
(vi)
False. On heating, we are adding energy to the camphor, and this energy increases the movement of the particles causing them to spread throughout the room. The smell is due to the camphor particles spreading, not energy being released as smell.
Q3Keep the curiosity alive
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.
Solution
The correct answer is (iii) Nothing of the chair will remain. The chair is made up of constituent particles. If all the constituent particles are removed, there will be nothing left, and the chair will cease to exist.
Q4Keep the curiosity alive
Why do gases mix easily, while solids do not?
Solution
Gases mix easily because the interparticle attractions are negligible, and the particles move freely in all directions with maximum interparticle space. Solids, on the other hand, have strong interparticle attractions and fixed positions, restricting their movement and preventing them from mixing easily.
Q5Keep the curiosity alive
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.
Solution
Milk is a liquid and has a definite volume but no fixed shape. The particles in liquids can move freely within a limited space, allowing it to flow and take the shape of the surface it is on. The glass tumbler is a solid and has a fixed shape and volume due to strong interparticle attractions holding the particles in fixed positions. Therefore, it retains its shape when milk is spilled.
Q6Keep the curiosity alive
Represent diagrammatically the changes in the arrangement of particles as ice melts and transforms into water vapour.
Solution
As ice (solid) melts into water (liquid), the particles gain energy and vibrate more vigorously. The strong interparticle forces weaken, allowing the particles to move past each other, increasing the interparticle spacing. As water (liquid) transforms into water vapor (gas), the particles gain even more energy. The interparticle forces become negligible, and the particles move freely in all directions with maximum interparticle spacing.
Q7Keep the curiosity alive
Draw a picture representing particles present in the following:
(i)
Aluminium foil
(ii)
Glycerin
(iii)
Methane gas
Solution
(i)
Aluminium foil (solid): The particles should be drawn closely packed in a regular arrangement.
(ii)
Glycerin (liquid): The particles should be drawn close together but with some spaces and in a random arrangement, showing they can move around.
(iii)
Methane gas (gas): The particles should be drawn far apart in a random arrangement, showing free movement in all directions.
Q8Keep the curiosity alive
Observe Fig. 7.16a 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. 7.16b showing the arrangement of particles.
Solution
In Fig. 7.16a, the solid wax of the candle represents the solid state with particles closely packed in a fixed arrangement. The molten wax represents the liquid state with particles close together but able to move past each other. The wax vapor represents the gaseous state with particles far apart and moving freely in all directions.
Q9Keep the curiosity alive
Why does the water in the ocean taste salty, even though the salt is not visible? Explain.
Solution
The water in the ocean tastes salty because salt particles are dissolved in it. When salt dissolves in water, it breaks up into its constituent particles, which are so small that they cannot be seen with the naked eye. These particles occupy the interparticle spaces between the water molecules, resulting in a uniform solution where the salt is not visible but its presence is sensed by taste.
Q10Keep the curiosity alive
Grains of rice and rice flour take the shape of the container when placed in different jars. Are they solids or liquids? Explain.
Solution
Grains of rice and rice flour are solids, not liquids. While they take the shape of the container, this is because they are a collection of individual solid particles. Liquids take the shape of the container because the individual particles can move freely and conform to the container's shape. Rice grains and flour do not flow or spread out like a liquid, and each grain maintains its solid form.