NCERT Exemplar Class 9 Science Solutions Chapter 1 Matter in Our Surroundings

NCERT Exemplar Class 9 Science Solutions Chapter 1-MCQ

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 gases
(d) Evaporation, solubility, diffusion, compression of gases

Answer:c

Temperature is the measurement of kinetic energy of particles or molecules for any substance, so on increasing temperature their kinetic energy increases.
The process of diffusion means intermixing of molecules of two different gases, which will definitely increase on increasing temperature.
In process of evaporation liquid molecules get converted into its vapor, for which they need energy which can be supplied by increasing temperature.
Generally solubility also increases by increasing temperature.
Thermal expansion is a general phenomenon which is observed in all the matters including gases liquids or solids and they will increase their volume on increasing temperature.
Hence the correct answer is option C

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

Ideally a gas does not have interaction between molecules by any kind of force. In real gases these forces are present and can be decreased by decreasing pressure and increasing temperature. Therefore any natural gas will behave as an ideal gas, if its temperature is increased and pressure is decrease.
On the other hand if we decrease the temperature and increase the pressure the interactions between gas molecules will increase and it will tends to liquefy.
Hence the correct answer is C.

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 and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids

Answer:C

The intermolecular force among the molecules of a solid is very strong so molecules cannot change its position on increasing temperature. These molecules of solid can vibrate at their own place but cannot leave their place hence they have rigidity.
On the other hand, the intermolecular force among the molecules of liquid and gases are small, so these liquids and gases can acquire the shape of the vessel and can flow easily.
Hence the correct answer of this question is option C.

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

The old Indian method to cool down the water is, Storing water in earthen pots.
These pots have pores in it by which evaporation of water take place.
In this Phenomenon, some water molecules get energy from the remaining water molecules in the pot and evaporate. Escape of high energy molecules from water leads to loss of heat from remaining water. As the remaining water loses heat, its temperature decreases.
Transpiration is the phenomenon of water movement and evaporation in the plants.
In case of diffusion, the molecules of matter moves from higher concentration to lower concentration.
In osmosis, the solvent tends to move through a semi permeable membrane from low concentration to high concentration.
Hence the correct option is D.

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

The intermolecular forces and its strength defines the state of matter.
Strong molecular forces leads the substance to be a solid, moderate molecular forces makes it liquid and the weakest or no intermolecular forces makes it gas.
Hence we can say the intermolecular forces increases, if the state of matter changes from gases to liquid to solid.
Air, oxygen and wind are gases.
Water, oil and juice are liquids.
Sugar and salt are solids.
Hence the correct answer is C

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

Celsius scale of temperature is based on water and its state. The melting point is taken as zero reference and boiling point of water is taken as 100.
Kelvin scale of temperature is known as absolute temperature scale.
These two scales can be easily related by a linear relation.
If temperature in Celsius scale is X then the same temperature in Kelvin scale will be X +273.
We have 25°C, 38°C and 66°C.
On conversion, these temperatures will be 298K, 311K and 339K respectively.
Hence the correct answer will be option A

Question:7

Choose the correct statement of the following
(a) conversion of solid into vapours without passing through the liquid state is called sublimation.
(b) conversion of vapours into solid without passing through the liquid state is called vapourisation.
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.

Answer:A

When the temperature of the gas decreases, at a particular temperature the gas get liquefy, this phenomenon is called condensation. If we further decrease the temperature of liquid, the liquid get converted into solid, this phenomenon is called freezing.
On the other hand if we increase the temperature of a solid, at a particular temperature it get liquefy, this phenomena is called melting. If we further increase the temperature of the liquid, it get converted into vapor, this phenomenon is called boiling.
But some solids shows exceptional behavior on increasing their temperature, they can directly convert into gases without acquiring intermediate liquid state. This phenomenon is called sublimation.
Hence the correct answer is option A.

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

Celsius scale of temperature is based on water and its state. The melting point is taken as zero reference and boiling point of water is taken as 100.
Kelvin scale of temperature is known as absolute temperature scale.
These two scales can be easily related by a linear relation.
If temperature in Celsius scale is X then the same temperature in Kelvin scale will be X +273.
The boiling points of diethyl ether, acetone and n-butyl alcohol are given as 35°C, 56°C and 118°C respectively
On conversion, their temperatures will be 308K, 329K and 391K.
Hence the correct answer will be option A

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

In case of evaporation, some liquid molecules take energy from rest of the liquid molecules and get converted in vapour.
If we increase the temperature of any liquid, it would be easy for some molecules to take the energy from rest of the molecules. As at higher temperature, all of them have higher amount of energy which will help process of evaporation.
The process of evaporation will be supported by exposure of surface to the surrounding, hence higher surface area leads to higher evaporation.
When we add common salt in water, some part of this salt covers the surface area along with water molecules which will create obstacles in evaporation.
Hence the correct answer of this question is option A.

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

Molecules of gas acquire the complete volume of container.
These molecules move randomly inside the container, therefore the average molecular separation can be calculated by assuming the given number of molecules in given volume.
It is easy to understand, that the average molecular separation will increase by either increasing the volume keeping number of molecules constant or by decreasing number of molecules keeping volume constant.
Increasing pressure will lead to increase in temperature of a gas in closed container. This will increase the kinetic energy of molecules. Therefore, it will not help in increasing distance between molecules.
Hence statement numbers (i) and (iii) are correct which will lead to correct answer as option C.

NCERT Exemplar Class 9 Science Solutions Chapter 1-Short Answer

Question:11

A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.

Answer:

At one atmospheric pressure condition, pure water start boiling at 100°C and it freezes at 0°C.
If we add some impurity in pure water, it leads to elevation in boiling point and depression in freezing point.
That means, water will boil at temperature more than hundred degrees centigrade And freeze at temperature lower than 0°C.
Hence we can say the given water is not pure and it will freeze at some temperature less than 0°C.

Question:12

A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time. Which of the following (Fig. 1.1) would correctly represent the result? Justify your choice.

Answer:

Ice and water can coexist at 0°C which is melting point of ice. As stated in the question, initially the container has ice as well as water, therefore the initial temperature has to be 0°C.
When we start giving heat to this mixture, the temperature will remain constant, because ice will melt by using the given heat.
When the complete ice will melt and container will have only water at 0°C, The heat given will lead to increase in temperature.
If we assume that heat given has a constant rate, then after that temperature increases linearly.
Hence the correct answer is option D

Question:13

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 vapour 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
a) In process of evaporation, some molecules of liquid take energy from rest of the molecules and get converted in vapour. Therefore, the energy of remaining liquid decreases which leads to decrease in temperature.
Hence we have to fill the blank space by COOLING
b) The intermolecular force among the molecules of solids is maximum among all three states.
Force in solids are more than intermolecular force among the molecules of liquid.
On the same line intermolecular forces among the molecules of liquid is more than force between gas molecules.
Hence we have to fill the blank space by STRONGER.
c) In solids, particles are arranged in perfect order. In liquid, molecules are less ordered and in gases they are totally random.
Hence at the first place we have to fill LIQUID and in second space we have to fill the GASEOUS.
d) In the process of sublimation, solids change to gaseous state without going through the liquid state.
Hence first place is filled with sublimation and the second space is filled with liquid.
e) At every temperature of liquid, some molecules of liquid gets converted into vapour.
This process is called evaporation.
Hence we have to fill the space with evaporation.

Question:14

Match the physical quantities given in column A to their S I units given in column B

Answer:

(a—iii) (b—iv) (c—v) (d—ii) (e—i)
Pressure is defined as normal force per unit area. Hence, its unit is newton per metre square. This is also known as Pascal.
The unit of temperature in SI unit system is Kelvin.
Density is defined as ratio of mass and volume, hence its SI unit is kilogram per cubic meter.
The SI unit of mass is kilogram.
Volume is the measurement of three-dimensional space covered by any object hence its unit is cubic meter.

Question:15

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:
(A) (B)
(a) degree celsius (i) kilogram
(b) centimetre (ii) pascal
(c) gram per centimetre cube (iii) metre
(d) bar (iv) kelvin
(e) milligram (v) kilogram per metre cube

Answer:

(a—iv) (b—iii) (c—v) (d—ii) (e—i)
Temperature can be measured in degrees Celsius or Kelvin or Fahrenheit.
Length is measured, in meter as per SI unit system and in centimetre as per CGS unit system.
Gram per centimetre cube and kilogram per metre cube, both are units of density in CGS system and SI system respectively.
Bar and Pascal are units to measure the pressure.
Milligram and kilogram are the units of mass.

Question:16

‘Osmosis is a special kind of diffusion’. Comment.

Answer:

In diffusion of liquid or gases, the particles move from higher concentration to low concentration.
In the process of osmosis, solvent goes through a semipermeable membrane from low concentration to high concentration.
In both cases, the particles wants to equate the concentrations. Therefore, we can say osmosis is a special kind of diffusion.

Question:17

Classify the following into osmosis/diffusion
(a) Swelling up of a raisin on keeping in water.
(b) Spreading of virus on sneezing.
(c) Earthworm dying on coming in contact with common salt.
(d) Shrinking of grapes kept in thick sugar syrup.
(e) Preserving pickles in salt.
(f) Spreading of smell of cake being baked through out the house.
(g) Aquatic animals using oxygen dissolved in water during respiration.

Answer:

(a)(c)(d)(e) – Osmosis (b)(f)(g) - Diffusion

A) When a raisin is kept in water, the water concentration will be smaller in raisins. Therefore, through the semipermeable membrane of raisin, water goes into the raisin. This is defined as Osmosis.
Due to excess of water the phenomenon of swelling occurs.
B) The concentration of virus in the air which comes out from the mouth during sneezing is very high.
These viruses get diffused in the ambient because of difference in concentration.
C) In salty water, due to osmosis, water from body of earthworm comes out. This leads to bursting of cells in body of earthworm and it dies.
D) When grapes are kept in thick sugar syrup, the water concentration will be less in sugar syrup. Due to osmosis, water from grapes comes out to the sugar syrup and the grapes shrink in this process.
E) Due to salt water from fruits or vegetables comes out by process of osmosis. This prevents oxidation of fruits and vegetables. Therefore, these pickles can be preserved for long.
F) When we bake a cake, the smell contained particles diffuse in ambient atmosphere. This occurs due to diffusion: particles move from high to low concentration.
G) Aquatic animals use oxygen, dissolved in water during respiration. This water has higher concentration of oxygen than blood. This difference in concentration causes diffusion of oxygen in to the blood.

Question:18

Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.

Answer:

When heat is released from our body, this effect cools down the body.
When heat is absorbed by our body, this effect heats up the body and burn it.
When water comes in contact as ice, it has low energy so heat from body goes to ice and causes cooling effect.
When steam come in contact with body, it gives heat to the body which causes burn. Steam at 100⁰C has more energy than water at 100⁰C.

Question:19

Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.

Answer:

In the process of boiling, water converts into steam by absorbing heat but without changing temperature. This heat is called latent heat of evaporation and it is possessed by vapour molecules.
Hence even water in boiling state and steam have same temperature, the energy of vapour molecules is more than water.
This is the reason, why Steam causes more burning than boiling water even they have same temperature.

Question:20

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.

Answer:

When hot water tumbler is kept in freezer, the temperature of water decreases as it loses energy to the freezer. The decrease in temperature of water goes up to 0°C. The water still loses energy to refrigerator as its temperature is less than 0°C, but this loss of energy will change the phase of water and it get converted in ice.
Till the time all water get converted in ice, temperature remained constant at 0°C.
After complete formation of ice, the ice will cool down to lower temperature until it equates with temperature of refrigerator.
Hence, the correct graph of temperature is given in option A.

Question:21

Look at Fig. 1.3 and suggest in which of the vessels A, B, C or D the rate of evaporation will be the highest? Explain.

Answer:

The process of evaporation will be more if surface area of water is more.
In the process of evaporation, some water molecules gets converted in vapour and remain above the liquid surface. With the help of high-speed air, these molecules of vapour can be taken away. This removal of vapour molecules, causes other water molecules to come out in form of vapour.
Hence we can say open container will show more evaporation in presence of high speed air.
Therefore, In case C, rate of evaporation will be maximum.

Question:22

(a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?

Answer:

A) The opposite of sublimation is generally known as de-sublimation. It is also known as deposition. In this Phenomenon, vapour get converted into solid directly without having liquid state.
B) At melting point of a solid, if we supply heat then it is used in changing solid state to liquid state without changing temperature.
This phenomenon is called fusion and this given heat is called latent heat of fusion.
Water at 0°C has more energy than ice at 0°C because of this latent heat of fusion.

NCERT Exemplar Class 9 Science Solutions Chapter 1-Long-Answer

Question:23

You are provided with a mixture of naphthalene and ammonium chloride by your teacher. Suggest an activity to separate them with well labelled diagram.

Answer:

Only polar compounds dissolve in water.
When nonpolar compound is mixed with water it gets precipitated.
We are given a mixture of naphthalene and Ammonium chloride.
We know that naphthalene is a non-polar compound and ammonium chloride is a polar compound.
If you make water solution of the mixture of naphthalene and ammonium chloride, the naphthalene with precipitate and ammonium chloride will dissolve.
So by the process of decantation, using funnel and filter paper, we can separate naphthalene.
Ammonium chloride is volatile at higher temperature. Hence, by the process of evaporation we can find out dry ammonium chloride from aqua solution.

Question:24

It is a hot summer day, Priyanshi and Ali are wearing cotton and nylon clothes respectively. Who do you think would be more comfortable and why?

Answer:

In season of summers the body tries to cool down itself by sweating. In this process, body excrete water from the skin and this water get evaporated and cools down the body.
In case of evaporation, some liquid molecules take energy from rest of the liquid molecules and get converted in vapour.
Cotton clothes absorb the water, and water gets evaporated through their surface. This will help to cool down the body temperature.
Nylon clothes does not absorb water, and create obstacles in process of evaporation.
Hence in season of summers it is advised to wear cotton clothes which will be more comfortable.

Question:25

You want to wear your favorite shirt to a party, but the problem is that it is still wet after a wash. What steps would you take to dry it faster?

Answer:

The wet clothes loses water by the process of evaporation.
The process of evaporation, depends on surface area and temperature as well as high-speed of air.
By increasing any of the above we can increase the rate of evaporation.
If we have to speed up the process of evaporation for quick drying of clothes we can use following steps.
We can dry our clothes in front of high speed fan, which will help the process of evaporation.
We can increase the surface area, by opening it completely at the time of drying.
We can definitely increase the evaporation by exposure of sunlight if it is available.
We can use hot iron to press the clothes as heat increases the rate of evaporation.

Question:26

Comment on the following statements:
(a) Evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(c) Sponge though compressible is a solid.

Answer:

a) In the process of evaporation, some molecules of liquid takes energy from other liquid molecules. By absorbing this energy, these molecules got converted in vapour.
By this process, the remaining liquid molecules will have lesser amount of energy. This decrement in energy causes cooling of liquid.
b) In the process of evaporation, liquids get converted in vapour. This Phenomenon stops after sometime due to high concentration of vapour above water surface.
At this time, sufficient number of vapour molecules are present above the liquid surface.
In humid atmosphere, water vapour molecules have high concentration. This high concentration of vapour, opposes the process of evaporation. Hence, it is difficult to evaporate in humid ambient.
c) Sponge is undoubtedly a solid as it has definite shape and volume unlike gases and liquids.
But sponge have some pores in it, where air is trapped.
When we tried to squeeze the sponge, the trapped air leaks out.
Then the space of air is occupied by the sponge, which causes it to shrink.
Therefore, it is compressible even if it is solid.

Question:27

Why does the temperature of a substance remain constant during its melting point or boiling point?

Answer:

The energy possessed by gases is more than liquids and similarly liquid possess more energy than solids.
When we heat up any solid at its melting temperature it keeps on receiving heat but its temperature does not change. The given heat is used to change the state of solid to liquid and this heat is called latent heat of fusion.
Similarly, when we heat liquid at its boiling point the temperature of liquid does not change. The given heat is used to change the state of liquid to gas and this heat is called latent heat of evaporation.
Generally heating results as rise in temperature but at boiling point and at melting point this is not observed. The heat given is used in state change.