RBSE Class 9 Science Important Questions Chapter 1 Matter in Our Surroundings

Rajasthan Board RBSE Class 9 Science Important Questions Chapter 1 Matter in Our Surroundings Important Questions and Answers.

RBSE Class 9 Science Chapter 1 Important Questions Matter in Our Surroundings

Objective Type Questions

Question 1.
Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gas
(d) Evaporation, solubility, diffusion, compression of gases
Answer:
(c) Evaporation, diffusion, expansion of gas

Question 2.
Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions :
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
Answer:
(c) Low temperature, high pressure

Question 3.
The property to flow is unique to fluids. Which one of the following statements is correct?
(a) Only gases behave like fluids
(b) Gases anü solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids
Answer:
(c) Gases and liquids behave like fluids

Question 4.
During summer, water kept in an earthen pot becomes cool because of the phenomenon of:
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation
Answer:
(d) evaporation

Question 5.
A few substances are arranged in the increasing order of forces of attraction between their particles. Which one of the following represents a correct arrangement?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air
Answer:
(c) Oxygen, water, sugar

Question 6.
On converting 25°C, 38°C and 66°C to Kelvin scale, the correct sequence of temperature will be :
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K
Answer:
(a) 298 K, 311 K and 339 K

Question 7.
Which of the following cannot be considered a form of matter?
(a) Atom
(b) Humidity
(c) Water
(d) Electron
Answer:
(b) Humidity

Question 8.
The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in Kelvin scale?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K
Answer:
(c) 308 K, 329 K, 391 K

Question 9.
Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water
Answer:
(a) Increase in temperature of water

Question 10.
In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container.
(ii) Some hydrogen gas leaking out of the container.
(iii) Increasing the volume of the container of hydrogen gas.
(iv) Adding more hydrogen gas to the container without increasing the volume of the container.
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer:
(c) (ii) and (iii)

Question 11.
Which of the following phenomena always results in the cooling effect?
(a) Condensation
(b) Evaporation
(c) Sublimation
(d) None of these
Answer:
(b) Evaporation

Question 12.
Which of the following causes the temperature of a substance to remain constant while it is undergoing a change in its state?
(a) Latent heat
(b) Lattice energy
(c) Loss of heat
(d) None of these
Answer:
(a) Latent heat

Question 13.
What is the melting point of pure ice?
(a) 273° C
(b) 273 K
(c) 373 K
(d) 100°C
Answer:
(b) 273 K

Question 14.
CNG is used for:
(a) cooking food
(b) in vehicles
(c) in hospitals
(d) in laboratories
Answer:
(b) in vehicles

Question 15.
Pascal is the unit of:
(a) density
(b) weight
(c) temperature
(d) pressure
Answer:
(d) pressure

Question 16.
Fill in the blanks :
(a) Evaporation of a liquid at room temperature leads to a …………. effect.
(b) At room temperature the forces of attraction between the particles of solid substances are …………. than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the …………… state. However, there is no order in the …………… state.
(d) ……………. is the change of solid state directly to gaseous state without going through the …………… state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called ……………
Answer:
(a) cooling
(b) stronger
(c) liquid, gaseous
(d) Sublimation, liquid
(e) evaporation

Question 17.
Match the physical quantities given in column A to their SI units given in column B :

Column A	Column B
(a) Pressure	(i) Cubic metre
(b) Temperature	(ii) Kilogram
(c) Density	(iii) Pascal
(d) Mass	(iv) Kelvin
(e) Volume	(v) Kilogram per cubic metre

Answer:
(a) – (iii)
(b) – (iv)
(c) – (v)
(d) – (ii)
(e) – (i)

Question 18.
The non-SI and SI units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity:

Column A	Column B
(a) Degree Celsius	(i) Kilogram
(b) Centimetre	(b) Pascal
(c) Gram per centimeter cube	(c) Metre
(d) Bar	(d) Kelvin
(e) Milligram	(v) Kilogram per cubic metre

Answer:
(a) – (iv)
(b) – (ii)
(c) – (v)
(d) – (ii)
(e) – (i)

Question 19.
Read the statements carefully and identify whether they are True or False
1. In summer, we should not wear cotton clothes.
2. The rate of evaporation is low when humidity is low.
3. Gases have low compressive properties.
4. All objects have mass and they occupy some space.
Answer:
1. False
2. False
3. False
4. True

Very Short Answer Type Questions

Question 1.
Why are light and sound not considered as matter?
Answer:
Light and sound are not considered as matter because they have no mass and do not occupy space.

Question 2.
A rubber band is a solid, but it can change its shape. Why?
Answer:
A rubber band changes shape under force and regains the shape when the force is removed, this is due to less intermolecular force of attraction between the particles.

Question 3.
When salt or sugar is poured into different kinds of vessels, why do they take the shape of vessel as they are solid?
Answer:
Salt or Suger takes the shape of containing vessel, but does not change its individual shape. For example – Sugar crystal is cubical and they remain cubical in any vessel.

Question 4.
What is plasma?
Answer:
Plasma is a state of matter consisting of super excited particles of very high energy level.

Question 5.
Express the boiling point of water in Celsius as well as Kelvin scale.
Answer:
100°C and 373 K.

Question 6.
What is diffusion?
Answer:
The intermingling of molecules of one substance with that of the other is called diffusion.

Question 7.
What happens to the rate of diffusion if the temperature is increased?
Answer:
With increased temperature, the rate of diffusion also increases as the particles gain energy and vibrate more.

Question 8.
Define melting point.
Answer:
The temperature at which a solid melts to become a liquid at an atmospheric pressure is called its melting point.

Question 9.
What is dry ice?
Answer:
Solid carbon dioxide obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.

Question 10.
What is humidity?
Answer:
The air holds water vapour, this air with water is called humid air and the amount of water vapour present in the air is called humidity.

Question 11.
What is normal atmospheric pressure?
Answer:
The atmospheric pressure at sea level is 1 atmosphere and taken as the normal atmospheric pressure.

Question 12.
What are fluids?
Answer:
The states of matter that can flow due to less intermolecular force of attraction are liquids and gases and are called fluids.

Question 13.
Define matter.
Answer:
Anything that occupies space and has mass and is felt by senses is called matter.

Question 14.
Give state of a matter if this substance has neither a fixed shape nor a fixed volume.
Answer:
Gas.

Question 15.
Predict the physical state of melting point of a substance is below the room temperature.
Answer:
Ice.

Question 16.
What do you mean by vapour?
Answer:
A substance that is found in gaseous state only at room temperature is called vapour.

Question 17.
State the effect of pressure on boiling point.
Answer:
Boiling point increases with increase in pressure.

Question 18.
Name any two substances which sublime.
Answer:
Camphor and naphthalene.

Question 19.
Define condensation.
Answer:
The change of gaseous state to liquid state on cooling is known as condensation.

Question 20.
Which is the slow process, evaporation or boiling?
Answer:
Evaporation.

Question 21.
What is the effect of surface area on rate of evaporation?
Answer:
If the surface area is increased, the rate of evaporation increases.

Question 22.
Write the SI unit of temperature.
Answer:
Kelvin.

Question 23.
Convert 10°C into Kelvin scale.
Answer:
273 + 10 = 283 K

Question 24.
Why evaporation is called surface phenomenon?
Answer:
Evaporation is called surface phenomenon as evaporation occur on the surface of liquid.

Question 25.
Name two processes from which it may be concluded that the particles of a gas move continuously.
Answer:
Diffusion and Brownian movement.

Question 26.
Name the state of water at 100° celsius, 0° celsius and 4° celsius.
Answer:
The state of water at 100° celsius is gas, at 0° celsius it is solid and at 4° celsius it is liquid.

Question 27.
The boiling point of alcohol is 78°C. What is this temperature on Kelvin scale?
Answer:
K= °C + 273 = 78 + 273 = 351 K

Short Answer Type Questions

Question 1.
Is it true to say that fluorescent tube contains plasma? Explain.
Answer:
It is right to say that fluorescent tube contains plasma. As fluorescent tube has helium or some other rare gases. The particles of the gas get ionised in the presence of high voltage applied. These charged particles are called plasma which glows.

Question 2.
What is the difference between a gas and plasma?
Answer:

1. Gas consists of neutral particles which are associated with energies comparable with atmospheric temperature.
2. Plasma contains energetic particles in the form of ionised gases.

Question 3.
Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Answer:
If we take some ice-cold water in a glass, after some time we will see small droplets of water deposited on the outer walls of the glass. Because water vapour present in air come into the contact of cold wall of glass, lose energy and converted into liquid state which can be seen in the form of small droplets.

Question 4.
A piece of chalk can be broken into small pieces when hammered but it is not possible in case of iron bar. Why?
Answer:
The force that keeps the particles together is lesser in chalk; hence it could be easily broken down into pieces on hammering. Whereas, the magnitude of this intermolecular force is more in iron, hence it cannot be broken into small pieces on hammering.

Question 5.
Explain, why solids have fixed shape but liquids and gases do not have fixed shape?
Answer:
Solids have fixed shape due to strong intermolecular force of attraction between them. The liquids and gases have molecules with less intermolecular force of attraction, and hence they can flow and take shape of the container.

Question 6.
Liquids and gases can be compressed but it is difficult to compress solids. Why?
Answer:
Liquids and gases have intermolecular space; on applying pressure externally on them the molecules can come closer thereby minimising the space between them. But in case of solids, there is no intermolecular space to do so.

Question 7.
Why do people perspire a lot on a hot humid day?
Answer:
On a hot humid day, due to the heat, our body starts sweating and gives cooling effect by evaporation. But the air cannot hold any more water on a humid day and therefore, the sweat or perspiration is seen.

Question 8.
Why is it advisable to use pressure cooker at higher altitudes?
Answer:
At higher altitudes, the atmospheric pressure is low and the water boils at a lower temperature which will take a lot of time to be cooked, therefore, the pressure is required to increase the cooking process and this is done by using pressure cooker which increases the pressure inside the container and stops the boiling of water at a lower temperature.

Question 9.
Why is the smell of the perfume of incense stick filled the whole room in few minutes, when lighted?
Answer:
When the incense stick is lighted the perfume particles are converted into gaseous form and acquire a larger kinetic energy. This kinetic energy makes the particles of the perfume to move rapidly. Thus, they easily drift through the air in the room and hence, we can smell it anywhere in the room.

Question 10.
What is latent heat of fusion?
Answer:
The heat required to change 1 kg of a solid substance into liquid state at the melting point of the substance. For example – Amount of heat required to melt ice at 0°C into water, so the temperature 0°C will be known as the latent heat of fusion of ice.

Question 11.
Two cubes of ice are pressed hard between two palms and after releasing the pressure, the cubes join together. Why?
Answer:
Pressure is directly proportional to temperature, when we apply pressure, temperature increases then the ice in contact melts below its melting point and it turns into water. When pressure is removed, the temperature decreases again and melted ice again freezes. Hence, cubes join together.

Question 12.
What is the reason that “Ice has lower density than water”?
Answer:
The mass per unit volume of a substance is called density (density = mass/volume). The density of substance decreases as the volume of a substance increases. Space between particles increases when water changes into ice. These spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice becomes greater as compared to the water. Hence, the density of ice becomes lower than that of water. And, a substance with lower density than water can float on water. Thus, ice floats on water.

Question 13.
Both the process of evaporation and boiling involves the change of state from liquid to gas but still they are different from each other. Justify.
Answer:
Evaporation is different from boiling as evaporation is a natural phenomenon, occurs on the surface of the water and also it is a slow process, whereas boiling is an artificial phenomenon, it occurs in the bulk of the liquid and is a fast process.

Question 14.
How can you show that evaporation causes cooling?
Answer:
When we put some acetone on our hand, after some time we will feel coolness on our hand because the acetone absorbs kinetic energy from our hand and evaporates and evaporation causes cooling.

Question 15.
What do you mean by latent heat of vaporisation?
Answer:
The latent heat of vaporisation of a liquid is the quantity of heat (in joules) required to convert 1 kilogram of the liquid to vapour or gas at its boiling point, without any change in temperature.

Question 16.
What property of gas is used when natural gas is supplied for vehicles?
Answer:
A gas is highly compressible and a large quantity of it can be compressed to a small, manageable volume. Thus, natural gas is compressed and is supplied for use by vehicles in the name of CNG (compressed natural gas).

Question 17.
Is it not proper to regard the gaseous state of ammonia as vapours? Explain.
Answer:
The gaseous state of a substance can be regarded as vapours only in case it is a liquid at room temperature. Since ammonia is a gas at room temperature, its gaseous state cannot be regarded as vapours. Naphthalene is volatile solid and has a tendency to sublime. So, it changes into vapours completely, thus disappears into the air and no solid is left.

Question 18.
State characteristics of matter demonstrated by :
(a) Diffusion,
(b) Brownian motion.
Answer:
(a) Diffusion involves movement of different particles so that they become intermixed uniformly.
(b) Brownian motion : It is the zig-zag movement of the small particles suspended in a liquid or a gas.

Question 19.
Why is water liquid at room temperature?
Answer:
At room temperature, the molecules of water have some intermolecular force of attraction and the room temperature cannot provide sufficient heat for these molecules to overcome their force of attraction and therefore, remain in liquid phase.

Question 20.
Cotton is solid but it floats on water. Why?
Answer:
Cotton has large number of pores where air is trapped. This process reduces cotton’s density and increases the volume. Therefore, cotton floats on water. But, when these pores get filled with water, it starts sinking.

Question 21.
On a hot sunny day, why do people sprinkle water on the roof or open grounds?
Answer:
During hot sunny day, the surface of roof or ground absorbs large amount of heat and remains hot. On sprinkling water on these surfaces, the water absorbs large amount of heat from the surface of roof and evaporates thereby causing cooling effect.

Question 22.
Why solid CO₂ is called dry ice?
Answer:
Solid CO₂ is stored at high temperature. When the measure of atmospheric pressure is 1 atm, then the solid CO₂ is directly converted to gas without coming in liquid state. Therefore, solid CO₂ is known as dry ice.

Question 23.
How is high compressibility property of gas useful to us?
Answer:
This property is used in the following situations

• LPG (liquefied petroleum gas) is a fuel which is made up of petroleum gas. On compressing this petroleum gas it forms liquid.
• Oxygen cylinders in the hospitals have compressed gas in it.
• CNG (compressed natural gas) is used as a fuel in vehicles and at home.

Long Answer Type Questions

Question 1.
Discuss the factors which affect evaporation.
Answer:
There are four factors which affect evaporation-

• Surface area: Escaping of particles from liquid state to vapour state depends. on surface area. Therefore, the rate of evaporation increases with surface area.
• Temperature : Higher the temperature, more will be the kinetic energy of substance and therefore, chance of escaping of particles is great from liquid to vapour state.
• Wind : The rate of evaporation increases with speed of wind.
• Humidity : Humidity is the amount of vapour present in the air. At fixed temperature, air cannot hold more than fixed amount of water vapour.

Therefore, the evaporation rate decreases if humidity is more in air.

Question 2.
Give difference between Evaporation and Boiling.
Answer:

Evaporation	Boiling
1. It takes place at any temperature.	1. It takes place at definite temperature called boiling point of liquid.
2. Temperature of liquid decreases during evaporation.	2. Temperature of liquid does not change during boiling.
3. Evaporation is a surface phenomenon; it takes place only at the surface of the liquid.	3. Boiling is the bulk phenomenon; it takes place in the whole mass of the liquid.
4. Evaporation is a slow and silent process.	4. Boiling is a rapid and violent process.

Question 3.
Explain the interconversion of three states in terms of force of attraction and kinetic energy of the molecules.
Answer:
The force working between the particles of a matter is called intermolecular force. Intermolecular forces are strong in solids and the particles are very close to each other they have least kinetic energy whereas in liquids, intermolecular force is less than solids and more than gases. As a result, there is more kinetic energy in liquid molecules because they are not held by strong force of attraction.

In gases, molecules are held together by weak Vanderwall forces. Thus molecules of a gas has maximum kinetic energy and least force of attraction.

Question 4.
The melting point of ice is 273.16 K. What does this mean? Explain in detail.
Answer:
Ice is solid at 0°C, i.e. 273 K. The molecules of ice are tightly packed. These molecules have to overcome the force of attraction with which they are held and hence, they gain this heat from the surrounding but the temperature remains the same as their energy is used to overcome the force of attraction between the particles. The particles of ice start vibrating freely and a stage reaches when the solid ice melts and is converted to liquid state at the same temperature, i.e. 273 K.

Question 5.
Pressure and temperature determine the state of a substance. Explain this in detail.
Answer:
Any matter, i.e. solid, liquid or gas when experiences an increase in temperature then they change their state.
Example:

When we take ice cubes in a beaker or heat them slowly, the temperature increases and ice melts to form liquid. When we heat this liquid further it will become steam. On lowering down the temperature of any matter, show changes in their state.
Example:

We take the steam that is coming out of boiling water and allow it to cool down, it condenses to form water and on further cooling of this water we get ice. On applying pressure and reducing temperature we can liquefy gases or change them into solid.

Example : We take carbon dioxide gas, reduce its temperature and apply lot of pressure on it so that it changes into solid carbon dioxide, called dry ice, which is used as refrigerant for cooling.

If pressure on it is decreased, it directly changes into gas.
In LPG cylinders, the petroleum gas is cooled and applying lot of pressure changes it into liquid state.
While using this LPG, we release the pressure exerted on it and hence, it comes out in the form of gas.

Question 6.
What is sublimation? Write an experimenttoexplain the process of sublimation.
Answer:
It is a process of conversion of substances directly from solid to gaseous state without coming in liquid state.

Experiment : Take a china dish, take mixture which contains ammonium chloride and salt and then cover it with glass conical funnel. Put a cotton cap on the other end solidified of the funnel so that vapour could not come out. Now put the china dish on burner. Since the ammonium chloride is sublimed after heating, it will be transformed straight into vapour and this vapour will again condense to form strong ammonium chloride in the upper hotter portion of the funnel. In this way, the sublimation can separate the ammonium chloride and salt mixture.

Question 7.
Explain the characteristics of particles of matter with examples.
Answer:
The characteristics of particles of matter are:

• Particles of matter have space between them- When we make tea or coffee, particles of one type of matter get into the spaces between particles of other. This shows that there is enough space between particles of matter.
• Particles of matter are continuously moving- When we light an incense stick, we can get the smell sitting at distance indicating that the particles are continuously moving.
• Particles of matter attract each other- When we try breaking the stream of water from a tap with fingers, we are not able to cut the stream which shows that particles of matter have force of attraction acting between them.

Question 8.
Explain with an activity which shows that the particles of matter are very small.
Answer:
Particles of matter are formed of small particles. To show this:

• Dissolve a few crystals of potassium permanganate in 100 mL of water.
• Take out approximately 10 mL of this solution and add it to 90 mL of clear water taken in another beaker.
• Now from this solution, again take 10 mL of the solution and add it to 90 mL of water taken in another beaker.
• In the same way, keep diluting the solution like this 5 to 8 times. It lightens the colour of water.

This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water. This proves that matter is made up of tiny particles and there must be thousands of tiny particles in just one crystal of potassium permanganate, which keep on diving themselves into smaller and smaller particles. At the end a stage is reached when the particles cannot divide further into smaller particles.

Fig. : Estimating how small are the particles of matter. With every dilution, through the colour becomes light, it is still visible.