CBSE
CHAPTER 1 MATTER IN OUR SURROUNDINGS
TEXTBOOK INTEXT QUESTION ANSWER
Question 1.Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
ANSWER: Anything that occupies space and has mass is called matter.
Chair,air, smell, almonds,cold drinks and the smell of perfume is matter.love, hate, thought,cold are not matter.
Question 2.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:This happens because rate of diffusion of gas increases with increase in temperature. In case of hot food, diffusion of smell is faster whereas in case of cold food, diffusion is slower.
Question 3.A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
ANSWER: This shows that matter is not continuous but is made up of particles which have space between them.
Question 4.What are the characteristics of the particles of matter?
ANSWER:The characteristics of particles of matter are:-
(a)Particle of matter have space between them.
(b)Particles of matter are continuously moving.
(c)Particles of matter attract each other.
Question 5.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:The increasing order of density is:
air < exhaust from chimney < cotton < water < honey < chalk < iron.
Question 6.
(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) The main characteristics of states of matter :
(b) (i) Rigidity : Tendency of a substance to retain and maintain its shape when subjected to outside force.
(ii) Compressibility: Compressibility is the ability to be reduced to a lower volume when force is applied.
(iii) Fluidity: fluidity is the ability to flow.
(iv) Filling a gas container: By filling a gas container mean the attainment of the shape of the containers by gas attainment.
(v) Shape: shape defines a definite boundary.
(vi) Kinetic energy: kinetic energy is the energy passed by a particle due to its motion.
(vii) Density: density is mass per unit volume.
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Question 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 the air, but to do the same through a solid block of wood, we need a karate expert.
ANSWER:(a) There is little attraction between particles of gas. Thus, gas particles move freely in all directions. Therefore, gas completely fills the vessel in which it is kept.
(b) Particles of gas move randomly in all directions at high speed. As a result, the particles hit each other and also hit the walls of the container with force. Therefore, gas exerts pressure on the walls of the container.
(c) A wooden table has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. Hence, a wooden table should be called a solid.
(d) Particles of the air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in the air, but to do the same through a solid block of wood, we need a karate expert.
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Question 4:
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
ANSWER: The mass per unit volume of a substance is called density (density = mass/volume). As the volume of a substance increases, its density decreases.
Though ice is solid, it has a large number of empty spaces between its particles. These spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice is greater than that of water. Hence, the density of ice is less than that of water. A substance with a lower density than water can float on water. Therefore, ice floats on water.
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Question 1:Convert the following temperature to Celsius scale:
(a) 300 K
(b) 573 K
ANSWER:
(a) 300 K = (300 − 273)°C
= 27°C
(b)573 K = (573 − 273)°C
= 300°C
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Question 2:What is the physical state of water at:
(a) 250°C
(b) 100°C
ANSWER:
(a) Water at 250°C exists in a gaseous state.
(b) At 100°C, water can exist in both liquid and gaseous form. At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from a liquid state to a gaseous state.
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Question 3:For any substance, why does the temperature remain constant during the change of state?
ANSWER: During a change of state, the temperature remains constant. This is because all the heat supplied to increase the temperature is utilized in changing the state by overcoming the forces of attraction between the particles. Therefore, this heat does not contribute to increasing the temperature of the substance.
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Question 4:Suggest a method to liquefy atmospheric gases.
ANSWER:
By applying pressure and reducing the temperature, atmospheric gases can be liquefied.
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Question 1:Why does a desert cooler cool better on a hot dry day?
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ANSWER: A hot dry day means that the temperature of the atmosphere is high and the humidity of the air is low. Both these factors increase the rate of evaporation and thus enormous cooling is produced.
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Question 2How does water keep in an earthen pot (matka) become cool during summer?
ANSWER: There are some pores in an earthen pot through which the liquid inside the pot evaporates. This evaporation makes the water inside the pot cool. In this way, water kept in an earthen pot becomes cool during summer.
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Question 3:Why does our palm feel cold when we put some acetone or petrol or perfume on it?
ANSWER: When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of the liquid absorb energy from the surrounding or the surface of the palm to compensate for the loss of energy, making the surroundings cool. Hence, our palm feels cold when we put some acetone or petrol, or perfume on it.
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Question 4:Why are we able to sip hot tea or milk faster from a saucer than a cup?
ANSWER: A liquid has a larger surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. For this reason, we are able to sip hot tea or milk faster from a saucer than from a cup.
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Question 5:What type of clothes should we wear in summer?
ANSWER: We should wear cotton clothes in summer. During summers, we sweat more. On the other hand, cotton is a good absorber of water. Thus, it absorbs sweat from our bodies and exposes the liquid to the atmosphere, making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.
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EXERSICE
Question 1:
Convert the following temperatures to Celsius scale.
(a) 293 K
(b) 470 K
ANSWER: Kelvin is an SI unit of temperature, where 0°C = 273.16 K (approximately 273 K)
(a) 293 K = (293 − 273) °C
= 20 °C
(b) 470 K = (470 − 273) °C
= 197 °C
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Question 2:
Convert the following temperatures to the Kelvin scale.
(a) 25°C
(b) 373°C
ANSWER: Kelvin is an SI unit of temperature, where 0°C = 273.16 K (approximately 273 K)
(a) 25 °C = (25 + 273) K
= 298 K
(b) 373 °C = (373 + 273) K
= 646 K
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Question 3:
Give a reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several meters away.
ANSWER:(a) Naphthalene undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily. Thus, naphthalene balls disappear with time without leaving any solid.
(b) Gaseous particles possess high speed and large spaces between them. Particles of perfume diffuse into these gaseous particles at a very fast rate and reach our nostrils. This enables us to smell the perfume from a distance.
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Question 4:Arrange the following substances in increasing order of forces of attraction between particles−− water, sugar, and oxygen.
ANSWER: Sugar is solid; the forces of attraction between the particles of sugar are strong.
Water is a liquid; the forces of attraction here are weaker than sugar.
Oxygen is a gas; the forces of attraction are the weakest in gases.
Thus, the increasing order of forces of attraction between the particles of water, sugar, and oxygen is Oxygen < Water < Sugar
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Question 5:What is the physical state of water at−−
(a) 25°C
(b) 0°C
(c) 100°C
ANSWER:
(a) Water at 25°C is present in the liquid state.
(b) At 0 °C, water can exist as both solid and liquid. At this temperature, after getting the heat equal to the latent heat of fusion, the solid form of water i.e., ice starts changing into its liquid form i.e., water.
(c) At 100 °C, water can exist as both liquid and gas. At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from its liquid state to its gaseous state, i.e., water vapors.
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Question 6:
Give two reasons to justify−
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
ANSWER:
(a) At room temperature (25 °C), water is a liquid because it has the following characteristic of a liquid:
(i) At room temperature, water has no shape but has a fixed volume i.e., it occupies the shape of the container in which it is kept.
(ii) At room temperature, water flows.
(b) An iron almirah is a solid at room temperature (25 °C) because:
(i) it has a definite shape and volume like a solid at room temperature.
(ii) it is rigid as solid at room temperature.
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Question 7:Why is ice at 273 K more effective in cooling than water at the same temperature?
ANSWER:Ice at 273 K has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.
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Question 8:What produces more severe burns, boiling water or steam?
ANSWER: Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.
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Question 9:
Name A, B, C, D, E, and F in the following diagram showing a change in its state.