IN-TEXT QUESTIONS SOLVED
Page No.- 3
Q1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
Answer: Almonds, air, cold-drink and chair.
Q2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: As the particles of hot food have more kinetic energy and hence the rate of diffusion is more than the particles of cold food. Hence the smell of hot sizzling food reaches severed meters away.
Q 3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer: A diver is able to cut through water in a swimming pool. This shows that the particles of water have more intermolecular space and has less force of attraction.
Q 4. What are the characteristics of the particles of matter?
Answer: The characteristics of the particles of matter are following:
(1) Particles of matter are moving continuously.
(2) Particles have intermolecular force.
(3) Particles have intermolecular space.
Page No.- 6
Q 1. The mass per unit volume of a substance is called density.
(density = mass/volume).
Arrange the following in order of increasing density:
Air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer: Increasing order of density:
air < exhaust from chimneys < cotton < water < honey < chalk < iron.
Q 2. (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer: (a) Difference in the characteristics of Three states of matter are as follows.
(b) Comment on:
(i) Rigidity: The tendency of a substance to maintain/retain their shape when subjected to any outside force.
(ii) Compressibility: The matter has intermolecular space between the particles. If the external force applied on the matter, that can bring these particles closer. This property is called compressibility. Gases are heghly compressible and liquids are less compressible than Gases and solids are negligibly compressible.
(iii) Fluidity: The tendency of particles of a matter to flow is called fluidity. Liquids and gases flow.
(iv) Filling of a gas container: The particles of gas vibrate randomly in all directions. So, The gas can fill the container.
(v) Shape: Solids have maximum intermolecular force and definite shape.
Whereas liquids and gases takes the shape of container.
(vi) Kinetic energy: The energy possessed by particles due to their motion is called kinetic energy. Molecules of gases vibrate randomly as they have maximum kinetic energy.
(vii) Density: It is defined as mass per unit volume, the solids have highest density.
Q 3. Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer: (a) Because the particles of gas have high kinetic energy they keep moving in all directions therefor they fill the vessel completely in which they are kept.
(b) Due to high kinetic energy, the molecules of the gas are in constant random motion. These Gas particles constantly vibrate, move and hit the walls of the container and hence exerting pressure on it.
(c) The molecules/particles of wooden table are tightly bounded with each other, there is no intermolecular space, it cannot be compressed, it cannot flow, all these characteristics are of solid. Therefore a wooden table should be called a solid. ‘
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert. It is because the molecules of air has less force of attraction between them and a very small external force can separate them and pass through it. But in case of solids, the molecules have maximum force of attraction, the particles are tightly bound due to this force. Hence large amount of external force is required to pass through solid.
Q 4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why?
Answer: Ice is a solid but its density is lower than water due to its structure. The molecules in ice make a cage like structure with lot of vacant spaces, this makes ice float on water.
Page No.- 9
Q 1. Convert the following temperature to Celsius scale:
(a) 300 K (b) 573 K
Answer:
Because, K- 273 = Degree C
(a) 300 – 273 = 27°C
(b) 573 – 273 = 300°C
Question.2. What is the physical state of water at:
(a) 250°C (b) 100°C
Answer: (a) 250°C = gas (b) 100°C liquid as well as gas
Q 3. For any substance, why does the temperature remain constant during the change of state?
Answer: During the change of state of any matter heat is supplied to the substance. The molecules of this matter use heat to overcome the force of attraction between the particles, at this period of time, temperature remains constant. This extra heat is acquired by the molecules in the form of hidden heat called latent heat to change from one state of matter to the other state.
Q 4. Suggest a method to liquefy atmospheric gases?
Answer: The atmospheric gases are taken in a cylinder with piston fitted on it. By cooling and applying pressure on them, the gases can be liquefied. The Process is shown in the figure below.
Page No.-10
Q 1. Why does a desert cooler cool better on a hot dry day?
Answer: The outer walls of the cooler get sprinkled by water constantly. This water evaporates due to hot dry air which present in hot dry weather. Evaporation causes cooling of inside air of cooler. This cool air is sent in the room by the fan.
Q 2. How does the water kept in an earthen pot (matka) become cool during summer?
Answer: The earthen pot is porous with lot of pores on it, the water oozes out through these pores and the water gets evaporated at the surface of the pot by absorbing the surrounding heat thereby it gives cooling effect. This makes the pot cold and the water inside the pot cools by this process.
Q 3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer: Petrol, acetone or perfume evaporate when they come into contact with air. The evaporation causes cooling sensation in our hands because during the evaporation, matter absorb the surrounding heat.
Q 4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer: Tea in a saucer has larger surface area than in a cup. As surface area increases the rate of evaporation become faster. The cooling of tea in saucer takes place sooner than in a cup. Hence we are able to sip hot tea or milk faster from a saucer rather than a cup.
Q 5. What type of clothes should we wear in summer?
Answer: We should wear light colored cotton clothes in summer. Because Light color reflects heat and
Cotton clothes has pores in it, which absorbs sweat and allows the sweat to evaporate faster and it gives cooling effect.