chemistry : class11 Density and Diffusion : Properties of hydrogen : Hydrogen MCQ Questions and Answers
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Density and Diffusion
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MCQ Questions
1. At the same temperature and pressure, what is the density of hydrogen relative to oxygen?
A.
1:4
B.
1:8
C.
1:16
D.
1:32
Correct Answer:
1:16
Explanation:
At identical temperature and pressure, gas density is proportional to molar mass. Since the molar masses of H2 and O2 are 2 and 32 respectively, the density ratio is 2:32, or 1:16.
2. Hydrogen and oxygen diffuse under identical conditions. If oxygen diffuses at 1 unit of rate, what is the diffusion rate of hydrogen?
A.
2 units
B.
4 units
C.
8 units
D.
16 units
Correct Answer:
4 units
Explanation:
By Graham's law, the rate of diffusion is inversely proportional to the square root of molar mass. Therefore, r(H2)/r(O2) = square root of (32/2) = 4.
3. A gas has a density nine times that of hydrogen at the same temperature and pressure. How many times faster does hydrogen diffuse than this gas?
A.
Three times
B.
Nine times
C.
One-third as fast
D.
One-ninth as fast
Correct Answer:
Three times
Explanation:
At the same temperature and pressure, density is proportional to molar mass. Thus the gas has a molar mass nine times that of hydrogen. Graham's law gives the rate ratio as the square root of 9, so hydrogen diffuses three times faster.
4. Hydrogen travels 40 cm through a porous partition in a certain time. How far will helium travel in the same time under identical conditions?
A.
20 cm
B.
28.3 cm
C.
40 cm
D.
56.6 cm
Correct Answer:
28.3 cm
Explanation:
The diffusion-rate ratio r(H2)/r(He) equals the square root of (4/2), which is square root of 2. Hence the distance travelled by helium is 40 divided by square root of 2, approximately 28.3 cm.
5. A gas takes four times as long as hydrogen to diffuse the same distance under identical conditions. What is the molar mass of the gas?
A.
8 g mol−1
B.
16 g mol−1
C.
32 g mol−1
D.
64 g mol−1
Correct Answer:
32 g mol−1
Explanation:
For the same distance, time is inversely related to diffusion rate. If the gas takes four times longer, hydrogen diffuses four times faster. Thus square root of (Mgas/2) equals 4, giving Mgas = 32 g mol−1.
6. Equal numbers of moles of hydrogen and oxygen are mixed at the same temperature and pressure. What is the density of the mixture relative to hydrogen?
A.
4.5 times
B.
8.5 times
C.
16 times
D.
17 times
Correct Answer:
8.5 times
Explanation:
For equal numbers of moles, the average molar mass of the mixture is (2 + 32)/2 = 17 g mol−1. Since hydrogen has molar mass 2 g mol−1, the density ratio is 17/2 = 8.5.
7. The density of hydrogen at 273 K and 1 atm is 0.0899 g L−1. What is its approximate density at 300 K and 1 atm?
A.
0.0817 g L−1
B.
0.0899 g L−1
C.
0.0988 g L−1
D.
0.1098 g L−1
Correct Answer:
0.0817 g L−1
Explanation:
At constant pressure, gas density is inversely proportional to absolute temperature. Therefore, density at 300 K equals 0.0899 × 273/300, which is approximately 0.0817 g L−1.
8. Hydrogen and oxygen escape through a tiny aperture under identical conditions. If the molar rate of escape of oxygen is 1 mol min−1, what is the molar rate of escape of hydrogen?
A.
0.25 mol min−1
B.
2 mol min−1
C.
4 mol min−1
D.
16 mol min−1
Correct Answer:
4 mol min−1
Explanation:
Effusion through a small aperture follows the same inverse square-root dependence on molar mass as diffusion. Thus the hydrogen-to-oxygen rate ratio is square root of (32/2) = 4.
9. A gas has one-half the density of oxygen at the same temperature and pressure. What is the ratio of its diffusion rate to that of hydrogen?
A.
1:4
B.
1:2
C.
2:1
D.
4:1
Correct Answer:
2:1
Explanation:
The gas has molar mass half that of oxygen, so its molar mass is 16 g mol−1. By Graham's law, its rate relative to hydrogen is square root of (2/16) = 1/2 for hydrogen-to-gas rate, meaning the gas diffuses twice as fast as hydrogen.
10. Gas X is four times as dense as gas Y at the same temperature and pressure. If gas Y diffuses 60 cm in a given time, how far will gas X diffuse in the same time?
A.
15 cm
B.
30 cm
C.
120 cm
D.
240 cm
Correct Answer:
30 cm
Explanation:
The diffusion-rate ratio r(X)/r(Y) equals the square root of the inverse density ratio, or 1 divided by square root of 4, which is 1/2. Therefore, gas X travels 60 × 1/2 = 30 cm.
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