Given below are the Class 9 Science CBSE Important questions for matter in our Surroundings
a) Very Short questions
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Question 1. 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
Question 3. 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
Question 4. 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
Question 5. Arrange the following substances in increasing order of intermolecular force of attraction:
water, sugar, oxygen Solution
Oxygen < Water < Sugar
Question 6. 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).
Question 7. Why does the temperature of a substance remain constant during melting and boiling even when heat is being supplied to it continuously?
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.
Question 8. Explain the diffusion of copper sulphate into water. Question 9. 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
Question 10. 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.
Question 11. 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
Question 12. 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
Question 13. 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
Question 14. 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
Question 15. (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
Question 16. 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 17. 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
Question 18. 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.
Question 19. 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 20. 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 21. 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 22. Give three examples of crystalline and amorphous solids. Solution
Question 23. Why is motor oil more viscous than water? Does motor oil have a greater surface tension than water. Question 24. Describe why a drop of food coloring in a glass of water slowly becomes evenly distributed without the need for stirring? Question 25. Liquid mix more slowly than gases. Why? Question 26. 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.