Class 9 Science CBSE Extra questions for matter in our Surroundings
Given below are the Class 9 Science CBSE Extra questions and answers for matter in our Surroundings
(a) Very Short Answer type
(b) Short Answer type
(d) Long answer type
(e) Foundation Level Questions for Olympiads/JEE Level/PMT/KVYP
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Very Short Answer type
A rubber band can change its shape on stretching. Will you classify it as solid or not? Justify? Solution
Rubber band changes shape under force and regains the shape when the force is removed. So, it is classified as a solid.
Sponge, though compressible, is a solid? Solution
A sponge has minute holes in which air is trapped. When we press it, the air is expelled out and we are able to compress it. On releasing pressure, it again regains its shape. So, it is classified as a solid.
Gases completely fill the vessel in which they are kept. Give reasons. Solution
In the gaseous state, particles move freely and have greater space between them. So they occupy the entire space available. Hence, gases completely fill the vessel in which they are kept.
Under what conditions gases can be liquefied? In which form LPG is filled in gas cylinder? Solution
By applying pressure and reducing temperature, gases can be liquefied. The liquefied petroleum gas (LPG) is filled in gas cylinders in the compressed gas form.
A solution of iodine in alcohol is known as tincture of iodine. Solute is iodine and solvent is alcohol.
Arrange the following substances in increasing order of intermolecular force of attraction:
water, sugar, oxygen Solution
Oxygen < Water < Sugar
Why does the temperature of a substance remain constant during melting and boiling even when heat is being supplied to it continuously? Solution
It is because the heat supplied to the substance is used up (or absorbed) in overcoming the intermolecular forces, and therefore, it does not show up as a rise in the temperature.
Why do the gases exert more pressure on the walls of the container than the solids? Solution
The particles of a gas move about randomly at very high speeds because of large spaces and very less attractive forces between them. Due to this the particles collide with each other and the walls of the container. Due to this collision gas exerts pressure on the wall of the container.
Why should we wear cotton clothes during summer? Solution
We perspire more during summer. Cotton is a good absorber of water. It absorbs sweat and exposes it for easy evaporation. As a result body feels cool and comfortable. So, we should wear cotton clothes during summer.
Why does a desert cooler cool better on a hot dry day? Solution
The humidity that is the amount of water vapours in air is less on a hot dry day. Lesser the humidity more is the rate of evaporation. Since the rate of evaporation is more on a hot dry day, a desert cooler cools better.
Short Answer type
Liquid generally have lower density as compared to solids, but ice floats on water. Find out, why. Solution
Ice and water both are the same substance but ice has greater volume than that of the same amount of water.
As density is inversely proportional to the volume, ice is less denser than water.
Objects having density less than water float on the surface of water.
Solid $CO_2$ is called dry ice, because solid $CO_2$ gets converted directly into gaseous state without coming into liquid state on decreasing pressure to one atmosphere.
Explain why temperature remains constant during interconversion of states of matter? Solution
Heat supplied to a substance is getting used during changing its state to overcome the force of attraction between the particles. The excess heat is absorbed by the particles in the form of latent heat.
Give reason to explain why it takes longer time to dry wet clothes in humid weather? Solution
Rate of evaporation depends on humidity present in air. Humid air already has large amount of water vapours, so rate of evaporation is slow.
Why do people sprinkle water on the roof after a hot sunny day? Solution
After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the surface. Water takes away the heat from the ground and gives cooling effect.
Write any three differences between evaporation and boiling? Solution
Why does ice at 0°C appear colder than water at same temperature? Solution
Particles in water at 0° C (273K) have more energy as compared to the particles in ice at the same temperature. It is due to the latent heat o fusion.
Why mixture does not have a fixed melting point or a fixed boiling point? Give two reasons? Solution
It does not have fixed composition and it does not have uniform ordered arrangement of particles.
On suffering from fever which will lower down your body temperature, more ice or ice cold water? Solution
Ice will lower down body temperature more because it will take latent heat of fusion from our body and fever will come down faster.
A gas exerts pressure on the walls of container, why? Solution
Gas molecules collide with each other as well as with the walls of container. Therefore, gas exerts pressure.
The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close. Solution
Solids diffuse at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into air increases. This is due to an increase in the kinetic energy of solid particles. Hence, the smell of hot sizzling food reaches us even at a distance, but to get the smell from cold food we have to go close.
Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density. Solution
What is the physical state of water at:
(b) 100°C Solution
Why does our palm feel cold when we put some acetone or petrol or perfume on it? Solution
Acetone, petrol, and perfume evaporate at low temperatures. When some acetone, petrol, or perfume is dropped on the palm, it takes heat from the palm and evaporates, thereby making the palm cooler.
Give 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. Solution
Naphthalene balls disappear with time without leaving any solid because they undergo sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily.
Perfumes has high degree of vaporization and its vapour diffuse into air easily. Therefore, we can get the smell of perfume sitting several metre away.
Give two reasons to justify-
(a)Water at room temperature is a liquid.
(b)An iron almirah is a solid at room temperature. Solution
Water at room temperature is a liquid because it has fluidity also it has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.
Iron almirah is a solid at room temperature it has rigid and fixed shape.
A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 00C). If you could measure the temperature of the content of the tumbler, which of the following graphs would correctly represent the change in its temperature as a function of time.
Since ice and water are in equilibrium, the temperature would be zero. When we heat the mixture, energy supplied is utilized in melting the ice and the temperature does not change till all the ice melts because of latent heat of fusion. On further heating, the temperature of the water would increase. Therefore the correct option is (d).
What is condensation? How is the condensation of a gas carried out? Solution
The process due to which gas convert into liquid state by giving out heat energy is called condensation.When a gas is compressed , it loses its heat energy thereby consequently decreasing the intermoleculer distance between the molecules and increasing the intermolecular force of attraction between the molecules .Thus resulting in condensation of gas
There is strong intermolecular force of attraction between molecules and there is very little space for the molecules to move around
Which state of matter is compressible? Why? Solution
Gaseous state of matter is compressible as there is large distance between the molecules of the gas and when pressure is applied on gas,the gas molecules come close and gas in total occupies less space
i.Convert the following Kelvin temperature to degrees Celsius.
a. 173 K
b. 273 K
c. 400 K
ii.Convert the following Celsius temperature to Kelvin temperature.
a. -73 ° C
b. -23 ° C
c. 100 ° C Solution
i. We know that ° Celsius = K - 273
a. ° C= $K - 273 = 173-273$ =-100 ° C
b. ° C= $K - 273 = 273 -273$= 0 ° C
c. ° C= $K - 273 =400 - 273$= 127° C
ii. We know that K = ° C + 273
a. K=° C + 273 = -73 + 273 = 200 K
b. K=° C + 273 = -23 + 273 = 250 K
c. K=° C + 273 = 100 + 273 = 373 K
Convert the following Kelvin temperature to degrees Celsius.
a. 175 K
b. 295 K
c. 300 K
d. 225 K Solution
a. Degree Celcius = K - 273 = 175-273=-98 0C
Convert the following Celsius temperature to Kelvin temperature.
a. 25 0C
b. -15 0C
c. 0 0C
d. 3 0C Solution
a. Kelvin = 0C + 273 = 298k
What is the physical state of water at the following temperatures?
(a) 25 0C
(b) 0 0C
(c) 100 0C Solution
(a) 25 0C: liquid
(b) 0 0C: solid or liquid (if melting process is on way).
(c) 100 0C: gas or liquid (if the boiling process is on way).
Long Answer type
The process in which a solid is converted directly into a gas is called sublimation. Iodine is an element that sublimes. A sample of solid iodine in a stoppered flask was allowed to stand undisturbed for several days. Crystals of solid iodine grew on the sides of the flask. Explain at the molecular level what happened? Question 36.
Give three examples of crystalline and amorphous solids. Solution
Question 37. Explain the diffusion of copper sulphate into water. Question 38. Why is motor oil more viscous than water? Does motor oil have a greater surface tension than water. Question 39. Describe why a drop of food coloring in a glass of water slowly becomes evenly distributed without the need for stirring? Question 40. Liquid mix more slowly than gases. Why? Question 41. Define the following terms:
a. Melting point
b. Freezing point
c. Boiling point Solution
a. The temperature at which solid changes into liquid is called its melting point.
b. The temperature at which liquid changes into solid.
c. The temperature at which liquid changes into vapors is termed as its boiling point.
Foundation Level Questions for Olympiads/JEE Level/PMT/KVYP
A constant pressure tank of gas at 1.01 Atm has propane in it at 150C when it is at 255 cubic meters. What is its volume at 480C? Solution
This can be found using Charles law which states that at constant Volume is directly proportional to temperature,So
255/288 = V/321
V=284.2 cubic meters
What is the mass of 15 liters of chlorine gas at STP? Solution
We know that one mole of any gas occupies a volume of 22.7 litres at STP. Thus
22.7 litres of chlorine gas at STP = 1 mole
1 litre of chlorine gas = (1 / 22.7) moles
15 litres of chlorine gas = (15 / 22.7) moles = 0.661 moles
Now, the molar mass of chlorine gas is 71g. This means that the mass of 6.023 X 1023 molecules of Cl2 gas is 71g. Thus
1 mole of chlorine gas = 71g
0.661 moles of chlorine gas = 71 X 0.661 = 46.916g
Thus the mass of 15 litres of Cl2 gas is 46.916g.
How many liters of hydrogen at 00C and 1400mm of Hg are produced if 15g of magnesium reacts with sulphuric acid? Solution
Given Pressure = 1400 mm of Hg =1400/760 atm= 1.842atm
R = 0.0821 L-atm/mol- K
no of moles= 15/24.305=.617
or V = nRT/P = 7.5L
A 250 Kg tank of liquid butane (C4H10) burns to produce carbon dioxide at 1200C. What volume of carbon dioxide is produced at 1 Atm? Solution
Similarly as above V=6.56 L
How many liters of product at 950 mmHg and 00C is produced by the burning of three liters of acetylene (C2H2) at 5 atm and 200C? Solution
A fixed quantity of gas at 230C exhibits pressure of 748 torr and occupies a volume of 10.3 L
a)Use Boyle's law to calculate the volume the gas will occupy at 230C if the pressure is increased to 1.88 atm.
b)Use Charles' law to calculate the volume the gas will occupy if the temperature is increased to 1650C while the pressure is held constant. Solution
a) As per Boyles laws, At constant temperature, Pressure is inversely proportional to Volume
P1=748 torr=748/760 atm=.984atm
b) As per Charles law which states that at constant Volume is directly proportional to temperature,So
10.3/298 = V/438
(a) Write the ideal- gas equat ion, and give the units used for each term in the equation when
Given that R = 0.0821 L-atm/mol- K
(b) What is an ideal gas? Solution
P= Pressure = atm
n=Number of Moles = moles
T= temperature =K
R =Gas constant=L-atm/mol- K
b) Ideal gas follows the ideal gas equation always
A certain volume of a gas is under a pressure of 900 mm of Hg. When the pressure is increased by 300 mm, the gas occupies 2700 ml. if this change occurs at a constant temperature, calculate the initial volume of the gas. Question 50.
At a pressure of 2 atmosphere a fixed mass of hydrogen occupies a volume of 8 liters. What pressure must be maintained if the volume is to be increased to 10 liters, temperature remaining constant? Question 51.
A given mass of a gas occupies 960 ml at 270C C. What volume will it occupy if the temperature is raised to 1770C C, pressure remaining constant?
Question 52. Crossword Puzzle
1. BEC stands for Bose-Einstein-______
3. The state consists of super energetic and super excited particles
8. Conversion of solid to vapour is called ______ Down
2. This is the phenomenon of change of a liquid into vapours at any temperature below its boiling point
4. SI unit of Temperature
5. CNG stands ____ natural gas
6. It is the amount of water vapour present in air.
7. LPG stands for ______petroleum gas. Solution
This matter in our surroundings class 9 extra questions with answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.
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