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3.GASES eLearn.Punjab

Q16 Helium gas in a 100 cm3 container at a pressure of 500 torr is transferred to a container with

a volume of 250 cm3. What will be the new pressure

a. if no change in temperature occurs (Ans: 2 0 0 torr)

b. if its temperature changes from 20 “C to 15°C? (Ans: 196.56 torr)

Q17
a. What are the densities in kg/dm3 of the following gases at STP
(P = 101325 Nm-2, T = 273 K, molecular masses are in kg mol-1
(i) methane, (ii) oxygen, (iii) hydrogen
b. Compare the values of densities in proportion to their mole masses.
c. How do you justify that increase of volume upto 100 dm3 at 27°C of 2 moles
of NH3 will allow the gas behave ideally, as compared to S.T.P conditions.
(Ans: CH4=0.714kgm, O2=1.428kgm-3, H2=0.089kgm-3)

Q18 A sample of krypton with a volume of 6.25 dm3 , a pressure of 765 torr and a temperature of 20 °C
is expanded to a volume of 9.55 dm3 and a pressure of 375 torr. What will be its final temperature in °C?

(Ans: T = -53.6°c)

Q19 Working at a vacuum line, a chemist isolated a gas in a weighing bulb with a volume of 255
cm3, at a temperature of 25 °C and under a pressure in the bulb of 10.0 torr. The gas weighed 12.1
mg. What is the molecular mass of this gas?

(Ans: 87.93g mol-1)

Q20 What pressure is exerted by a mixture of 2.00g of H2 and 8.00g of N2 at 273K in a 10 dm3 vessel?
(Ans: P = 2.88 atm)

Q21. a. The relative densities of two gases A and B are 1:1.5. Find out the volume of B which

will diffuse in the same time in which 150 dm3 of A will diffuse?

(Ans: 122.47dm3)

b. Hydrogen (H2) diffuses through a porous plate at a rate of 500 cm3 per minute at 0 “C. What
is the rate of diffusion of oxygen through the same porous plate at0 oC?

(Ans: 125 cm3)

c. The rate of effusion of an unknown gas A through a pinhole is found to be 0.279 times the

rate of effusion of H2 gas through the same pinhole. Calculate the molecular mass of the

unknown gas at STP. (Ans: = 25.7 gmol-1)

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