Class 9 Science Chapter 1 Matter in Our Surroundings

NCERT Class 9 Science Chapter 1 Matter in Our Surroundings, Question Answer to each chapter is provided in the list so that you can easily browse throughout different chapters Class 9 Science Chapter 1 Matter in Our Surroundings and select need one.

NCERT Class 9 Science Chapter 1 Matter in Our Surroundings

Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given SCERT Class 9 Science Chapter 1 Matter in Our Surroundings Solutions for All Subjects, You can practice these here.

Matter in Our Surroundings

Chapter – 1

GENERAL SCIENCE

1. Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

Ans. Chair, air, almonds and cold-drink are matter.

2. Give reasons for the following observation:

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. Particles in the air, if fueled with higher temperatures, acquire high kinetic energy, which aids them to move fast over a stretch. Hence, the smell of hot sizzling food reaches a person even at a distance of several meters.

3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Ans. A diver can cut through water in a swimming pool. The property of matter observed are this shows that the particles of matter have spaces between them. The intermolecular forces of attraction between liquid particles are not very strong, hence the diver’s force is enough to overcome these forces.

4. What are the characteristics of the particles of matter?

Ans. The characteristics of the particles of matter are:

(i) They have space between them. This space is called intermolecular space.

(ii) They are in constant motion. As a result, they possess kinetic energy.

(iii)  Particles of matter attract each other.

Textbook Page No. 6

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. Exhaust from chimneys, air, cotton, water, honey, chalk and iron.

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. are:

Ans.

(a) The differences in the characteristics of states of matter are.

(b) Rigidity: The tendency of matters to maintain their shapes when an outside force is applied to them is known as rigidity. Solids are highly rigid.Liquids flow and change shape. Hence, they are not rigid but called fluid. Gases are also fluids with very low density.

(c) Compressibility: Compressibility is the property of a matter by virtue of which its volume can be increased or decreased by reducing or increasing pressure upon it. Solids have negligible compressibility. Liquids can be compressed only to a small extent while gases are highly compressible.

(d) Shape: Shape refers to distinct boundaries. Solids have a definite shape, but liquids and gases do not have a definite shape.

(e) Kinetic energy: Kinetic energy is the energy possessed by the particles of a matter by the virtue of their motion. The kinetic energy of the particles of solids, liquids and gases are low, high and very high respectively.

(f) Density: Density is the measurement of how tightly a material is packed together. It is defined as the mass per unit volume. Density Symbol: D or ρ Density Formula: p = m/V, where ρ is the density, m is the mass of the object and V is the volume of the object.

3. Give reasons:

(a) A gas fills completely the vessel in which it is kept.

Ans: The intermolecular space between the particles of a gas is very large and the intermolecular force of attraction between the particles is negligible. Therefore, the particles are free to move randomly with high speed in all directions. So, a gas fills completely the vessel in which it is kept.

(b) A gas exerts pressure on the walls of the container.

Ans: The kinetic energy of the particles in the gaseous state is very large. Therefore, the particles are free to move randomly with high speed in all directions. In doing so, the particles continuously collide with each other and also with the walls of the container. As a result, they exert some force on the walls of the containing vessel. The force exerted by the gas particles per unit area on the walls of the container is the pressure exerted by the gas.

(c) A wooden table should be called a solid.

Ans: A wooden table should be called a solid because it has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. There is a strong force of attraction between molecules of wood and intermolecular space is the least.

(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.

Ans: We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert because the particles of air have large intermolecular spaces and least force of attraction between them. Thus, one can easily move the hand in air and push the particles of air apart.

4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Ans. When water freezes to form ice, some empty spaces are left between the water particles. Due to this, the density of ice (0•92 g cm-²) becomes less than water (1•0 g cm-³). As a result, ice floats on water.

Textbook Page No. 9

1. Convert the following temperate to celsius scale:

(a) 300 K

(b) 573 K

Ans. (a) We know,

2. What is the physical state of water at:

(a) 250°C.

Ans. (a) Gaseous state.

(b) 100°C.

Ans. Steam (or vapour)

3. For any substance, why does the temperature remain constant during the change of state?

Ans: The temperature remain constant the change of state are mentioned below:

(i) Temperature:

(a) Temperature is a feature of matter that represents the amount of energy of motion of its constituent particles.

(b) It is an estimate of how hot or cold a material is in comparison.

(c) Absolute zero is the coldest theoretical temperature.

(ii) Reason for constant temperature during change of state:

(a) Because the heat energy necessary to change the state of matter is used to break the intermolecular interactions and other attraction forces, the temperature is set during the change of state.

(b) Because the provided heat is adequate to raise the temperature of the substance and is used up to modify the state of matter of the substance, the temperature remains constant.

(iii) Latent heat:

(a) Latent heat is described as heat or energy absorbed or released during a substance’s phase shift.

(b) It could be from a gas to a liquid or from a liquid to a solid and vice versa. Enthalpy is a heat characteristic linked to latent heat.

4. Suggest a method to liquefy atmospheric gases.

Ans. Atmospheric gases can be liquefied by applying high pressure and reducing the temperature.

Textbook Page No. 10

1. Why does a desert cooler cool better on a hot dry day?

Ans. Evaporation causes cooling because due to evaporation, the high energy particles escape from the liquid surface leaving behind the low energy particles. As a result, the temperature of the liquid left behind decreases.

On a hot dry day, the rate of evaporation of water increases with increased temperature. Also, the humidity of air is low which increases the rate of evaporation. Therefore, due to the increased rate of evaporation on a hot dry day, a cooler cools better.

2. How does the water kept in an earthen pot (matka) become cool during summer?

Ans. The water kept in an earthen pot (matka) became cool during summer. 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 summers.

3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Ans. When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of the liquid absorb energy from 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.

4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Ans. We are able to sip tea or milk faster from a saucer because it has a larger surface area than the cup. In larger surface area rate of evaporation is faster due to which tea or milk cools rapidly.

5. What type of clothes should we wear in summer?

Ans. In summer, we should wear cotton clothes. During summer, there is a lot of sweat on our body. The sweat draws heat from our body. Cotton being a good absorber of water, absorbs the sweat and exposes it to atmosphere for evaporation leaving our body cool and dry.

EXERCISES (Textbook Page No. 12)

1. Convert the following temperatures to the celcius scale.

(a) 293 K.

(b) 470 K.

Ans. (a) We know,

2. Convert the following temperatures to the Kelvin scale.

(a) 25°C.

(b) 373°C.

Ans. (a) We know,

3. Give reason for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.

Ans: Naphthalene balls exhibit the phenomenon of sublimation. They directly change into gaseous state from the solid state without undergoing through the liquid state. Therefore, naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several metres away.

Ans: The particles of perfume diffuse with the particles of the air and move rapidly in all direction. Therefore, we can get the smell of perfume sitting several metres away.

4. Arrange the following substances in increasing order of forces of attraction between the particles-water, sugar, oxygen.

Ans. Oxygen<Water<Sugar.

5. What is the physical state of water at:

(a) 25°C.

Ans. liquid.

(b) 0°C.

(b) solid.

(c) 100°C.

Ans: vapour.

6. Give two reasons to justify:

(a) water at room temperature is a liquid.

Ans. (a) Water at room temperature is a liquid because:

(i) Water evaporates at 100° C and solidifies or freezes at 0°C. Hence, at room temperature it is a liquid.

(ii) it has no definite shape but has a definite volume. It takes the shape of the vessel in which it is kept.

(b) an iron almirah is a solid at room temperature.

Ans: An iron almirah is a solid at room temperature are mentioned below:

(i) The melting point of iron is very high at 1538° C and hence at room temperature it is a solid.

(ii) It has a definite shape and a definite volume.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Ans. Ice at 273 K (i.e. 0°C) has less quantity of heat due to its latent heat of fusion than water at 273 K. To melt 1 kg of ice at 273 K into water at 273 K, we require 3-35 x 10⁵J of heat energy which is taken from the substance. As a result, the substance loses heat to ice. Therefore, ice at 273 K is more effective in cooling than water at the same temperature.

8. What produces more severe burns, boiling water or steam?

Ans. Steam produces more severe burns. This is because, even though both boiling water and steam are of the same temperature [ 1000c] , the steam contains the extra latent heat of vapourisation. So. steam produces more severe burns.

9. Name A, B, C, D, E and F in the following diagram showing change in its state.

Ans. A – Fusion.

B – Vaporisation.

C – Condensation.

D – Solidification.

E – Sublimation.

F – Sublimation.

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