NCERT Solutions For Class 9 Science Chapter 1 Matter in Our Surroundings
NCERT Page No. 3 Q.
Q 1. Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.Ans. Matter : Anything which occupies space, have mass and can be felt by any one of our five senses is known as matter.
(A) In above given question following is matter : chair, air, smell, almonds, cold-drink, smell of perfume.
(B) Following are not matter love, hate, thought, cold.
Q. 2. Give reasons for the following observations :
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Ans. The smell of food reaches us due to the phenomena of diffusion. As the rate of diffusion of gases is very high so the particles of gas travel with high speed. The rate of diffusion of gas further increases on increasing temperature because the kinetic energy of particles of gases increases. Hence, the particles of hot vapour coming from hot sizzling food reaches to us from several metres away at faster speed. On the other hand, the particles of vapours coming from cold food can not diffuse faster and they travel slowly due to which, to get smell of cold food we have to go closer to the food.
Q.3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show ?
Ans. A diver is able to cut through water in a swimming pool. This observation explains the following property of water i.e., liquid state :
(1) The inter-particle forces of attraction in liquid state is not very strong.
(2) Liquids have somewhat larger interparticle spaces.
(3) Liquids have nature of fluidity i.e., the particles of liquid have freedom to move easily.
Q.4. What are the characteristics of the particles of matter?
Ans. The main characteristics of the particles of matter are as follows:
(1) The particles of matter are very very small.
(2) The particles of matter have inter-particle spaces between them.
(3) The particles of matter are moving constantly.
(4) The particles of matter have inter-particle forces of attraction.
(5) As the particles of matter are very small so they cannot be seen with the naked eyes.
NCERT 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.Ans. Actually, the density of a substance depends upon the no. of particles per unit volume as well as upon their mass.Density is different for different matter. The no. of particles is also related with their size and the force of attraction between them. On the basis of these three factors, i.e., no. of particles, size of particles and force of attraction the substances can be arranged in increasing order of density as follows
Air < exhaust from chimneys < cotton < water <honey < chalk < iron
Q. 2. (a) Tabulate the differences in the characteristics of states of matter.
Ans.(i)Solid is the state in which matter maintains a fixed volume and shape;
(ii) liquid is the state in which matter adapts to the shape of its container but varies only slightly in volume; and
(iii)gas is the state in which matter expands to occupy the volume and shape of its container.
(b) Comment upon the following: Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Ans. (i) Rigidity-It is the tendency to maintain the shape, when some outward force is applied. The rigidity is highest in solids. Any matter is said to be rigid when it has very small inter-particle spaces and very strong inter-particle force of attraction.
(ii) Compressibility-It is the tendency to decrease the volume on application of force. The compressibility is highest in gases because of the largest inter-particle spaces.
(iii) Fluidity-It is the tendency to flow. The fluidity is highest in gases due to very weak inter-particle force of attraction. Liquids also have tendency to flow but their fluidity is smaller than gases due to comparatively smaller inter-particle distances and larger inter-particle force of attraction.
(iv) Filling of a gas container-The gases can be compressed into very small volumes by applying large pressures. Due to its high compressibility,fairly large mass of a gas can be but in a small metal cylinders by compression. Such cylinders can be transported conveniently from one place to another. The cooking gas (L.P.G.) is also a form of compressed gas. The oxygen gas supplied to hospitals in cylinders is also the form of compressed form.
(v) Kinetic energy-It is the energy present in moving particle. In gases the interparticle spaces are large while interparticle force of attraction is small. Due to this reason, the particles of gases move with high speed hence, have highest kinetic energy. Kinetic energy of liquids is lesser than gases, while it is least in solids at room temperature.
Note-Kinetic energy is directly proportional to the temperature hence, as temperature increases kinetic energy of particles also increases.
(vi) Density-It is the mass occupied by a matter per unit volume. It can be obtain dividing the mass of a particular solid by the volume occupied by that mas solid. The unit of density is kg/l or kg/dm³ or g/ml or g/cm³.
(vii) Shape-The shape of the matter depends on the inter-particle force of attraction and inter-particle spaces. The solids have fixed shape due to strongest force of attraction and smallest inter-particle spaces while liquids do not have fixed shaped comparatively weaker force of attraction and larger inter-particle spaces.
Q. 3. Give reasons :
(i) A gas completely fill the vessel in which it is kept ?
Ans.(i) A gas in the vessel completely fills it in which it is kept due to the phenomen of diffusion. Actually, the particles of gas move freely in all directions with differ speeds. In gaseous state the inter-particle spaces are very large hence, they readily fill the vessel completely due to their motion.
(ii) A gas exerts pressure on the walls of the container ?
Ans. Force per unit area is called pressure. The particles of gas moving with high speed strike the wall of the container and exerts force as it Hence, we can say that the gas exerts pressure.
(iii) A wooden table should be called a solid ?
Ans. A wooden table should be called a solid because it has definite shape, fixed volume incompressible nature, rigidity and no movement of the constituent particles present in them.
(iv) We can easily move our hand in air but to do so the same through a solid block of wood we need a 'karate expert'.
Ans. The inter-particle spaces in air are very large while inter-particle force of attraction is very weak. This force is so weak that it can be overcome easily. It is the reason that our hand can move, in air. But the inter-particle spaces in solid are very small and inter-particle force of attraction is very strong. As a result this space cannot be easily overcome by the movement of our hand and thus only a 'karate expert' with highpower can separate the particles of 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 ?
Ans. Liquids generally have lower density as compared to solids. But the solid form of water i.e., ice floats on the surface of liquid water. It indicates that the density of solid form of water is lower than liquid form of water. This is due to open cage like structure of ice. It means, in ice some vacant spaces are left when H2O molecules get linked in ice. In water (liquid form) these vacant spaces are less. Theorefore due to larger vacant spaces the volume of ice increases hence, density decreases. Thus, it floats over the surface of water.
NCERT Page No. 9
Q. 1. Convert the following temperature to celsius scale.(a) 300K (b) 573K
Ans. The relation between kelvin scale and celsius scale is as follows:
T(K) = t(°C) + 273
hence,
(a) 300K = t(°C) + 273 t (°C) = 300 – 273
t = 27°C.
(b) 573K = t(°C) + 273
t(°C) = 573 – 273
t = 300°C.
Q. 2. What is the physical state of water at
(a) 250°C (b) 100°C
Ans. (a) The boiling point of water is 100°C. Therefore, the physical state of water at 250°C
i.e., the temperature higher than boiling point is gaseous state.
(b) At 100°C, which is the boiling point of water, water exists both as a liquid as well
as a gas.
Q. 3. For any substance, why does the temperature remain constant during the change of state ?
Ans. Once the change of state of a substance begins, the energy which is now supplied is being used up as latent heat or hidden heat, i.e., kinetic energy neither increases nor decreases. Now the heat supplied is used up to overome the inter-particle force of attraction. As a result the temperature remains constant during melting and boiling of a substance.
Q. 4. Suggest a method to liquefy atmospheric gases ?
Ans. Atmospheric gases can be liquified either by decreasing temperature or by increasing pressure. During liquefication of atmospheric gas the constituent particles have to be brought closer to each other i.e., interparticle spaces have to be decreased and interparticle force of attraction have to be increased. This can be done easily either by increasing pressure or by decreasing temperature.
NCERT Page No. 10
Q. 1. Why does a desert cooler cool better on a hot dry day?Ans. During hot and dry day the temperature of the atmosphere is high and humidity of air is low. The rate of evaporation increases as temperature increases and humidity decreases. Thus, desert cooler cools better on a hot dry day as in these days the rate of evaporation increases thus, cooling increases.
Q. 2. How is the water kept in an earthen pot (matka) become cool during summer ?
Ans. The water is kept in an earthen pot (Matka) become cool during summer due to the following reasons :
(i) The particles of water with high kinetic energy escapes through the pores of earthen pot (matka) and evaporates, since evaporation causes cooling, thus, the water cools.
(ii) In summer, the temperature is high so the rate of evaporation increases hence,cooling increases.
Q. 3. Why does our palm feel cold when we put some acetone or petrol or perfume on it ?
Ans. Acetone or petrol or perfumes are liquids with low boiling points, when they are put on palm then they quickly evaporates. The energy needed for evaporation is taken from the palm. As a result, the palm feels cold.
Q. 4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Ans. When hot tea or milk is poured in a saucer than the surface area increases due to which rate of evaporation increases and tea or milk becomes little cooler more quickly. Thus it becomes easier to sip hot tea or milk from a saucer rather than a cup. In cup the surface area of liquid is small therefore, evaporation occurs slowly hence, the liquid in the cup remains hot for a sufficient long time and we cannot sip tea or milk faster from cup.
Q. 5. What type of clothes should we wear in summer ?
Ans. In summer, we should wear cotton clothes because during summer we perspire more and cotton have tendency to absorb sweat more quickly and expose it to the atmosphere. As cotton clothes evaporates sweat which produce cooling and we feel comfort. Therefore, in summer cotton clothes helps us in keeping cool.
NCERT Solutions
Q. 1. Convert the following temperatures to the celsius scale: (a) 293 K (b) 470 K Ans. (a) 293 K
t(°C) = T(K)-273 = 293 - 273 = 20°C
(b) 470 K
t(°C) = T(K)-273 = 470 - 273 = 197°C
Q. 2. Convert the following temperatures to the kelvin scale.
(a) 25°C (b) 373° C
Ans. (a) 25°C
T(K) = t (°C) + 273 = 25 + 273 = 298 K
(b) 373° C
T(K) = t (°C) + 273 = 373 + 273 = 646 K
Q.3. Give reasons for the following observations:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Ans. (a) Naphthalene is a volatile solid which show sublimation at room temperature. As a result it gets converted into gaseous state. Therefore, Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfumes sitting several metres away because of diffusion process. During diffusion the particles of the perfume mix with the particles of air and reach us sitting several metres away.
Q. 4. Arrange the following substances in increasing order of forces of attraction between the particles-water, sugar, oxygen.
Ans. As we know that order of force of attraction between the constituent particles is as follows:
Solid > liquid > gas
Therefore, the force of attraction between particles in increasing order is as follows:
Sugar > water > oxygen
Q. 5. What is the physical state of water at: (a) 25°C (b) 0°C (c) 100°C
Ans. (a) At 25°C, the physical state of water is a liquid.
(b) At 0°C the physical state of water can be either a solid (ice) or a liquid.
(c) At 100°C the physical state of water can be either a liquid or a gas (steam).
Q. 6. Give two reasons to justify:
(a) Water at room temperature is liquid.
(b) An iron almirah is a solid at room temperature.
Ans. (a) Water is liquid at room temperature due to the following reasons:
(i) Water takes the shape of the vessel in which it is kept. So water does not have fixed shape, so it is a liquid.
(ii) Water can be poured from one vessel into another vessel. So water has fluidity i.e.it can flow as a liquid.
(b) An iron almirah is a solid at room temperature due to the following reasons:
(i) An iron almirah is hard and incompressible in nature that is, it has fixed shape, so it is a solid.
(ii) An iron almirah cannot diffuse on itself through air i.e., it can not diffuse so it is solid.
Q. 7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Ans. Ice (solid water) has extra energy in the form of latent heat of fusion (3.35 x 105 J/kg) as compared to water. Due to absorption of energy the temperature surroundings gets lowered or cooling is caused. Since water is already present in a liquid state so it does not absorb energy from the surroundings. Thus, ice at 273K causes more cooling than water at the same temperature.
Q. 8. What produces more severe burns, boiling water or steam ?
Ans. When water (liquid form) at 373 K is converted into steam at 373 K, it absorbs energy equal to latent heat of vaporisation (22.6 x 105 J/kg) from surroundings. Thus, steam (vapour form of water) at 373 K (100°C) have more energy then water at the same temperature and hence, steam produces more severe burns than boiling water.
Q. 9. Name A, B,C, D, E and F in the following diagram showing change in its state:
A = Fusion (melting)
B = Vaporisation
C = Condensation (Liquefication)
D = Solidification (freezing)
E = Sublimation
F = Sublimation (solidification of gaseous state)
tags: Class 9 Science Chapter 1, NCERT Solutions for Class 9, NCERT Solutions For Class 9 Science, NCERT Solutions For Class 9 Science Chapter 1, NCERT Solutions For Class 9 Science Chapter 1 Matter in Our Surroundings
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