Questions on Gas Density
Multiple-Choice Questions: Gas Density
(Assume STP conditions where needed: 1 atm, 0°C, 1 mol gas = 22.4 L)
Questions
1. What is the formula for the density (d) of a gas at STP?
A) d = PRT
B) d = mRT/P
C) d = PM/RT
D) d = RT/P
E) d = V/nRT
2. Which of the following gases will have the greatest density at STP?
A) Hydrogen (H₂)
B) Oxygen (O₂)
C) Nitrogen (N₂)
D) Carbon dioxide (CO₂)
E) Methane (CH₄)
3. What is the density of CO₂ at STP? (Molar mass = 44.0 g/mol)
A) 1.96 g/L
B) 2.55 g/L
C) 3.12 g/L
D) 4.10 g/L
E) 5.00 g/L
4. What is the unit of gas density in chemistry?
A) mol/L
B) g/mol
C) L/g
D) g/L
E) L/mol
5. Which of the following gases would be least dense at STP?
A) He
B) Ar
C) O₂
D) Cl₂
E) N₂
6. At constant temperature and pressure, density of a gas is directly proportional to:
A) Volume
B) Pressure
C) Molar mass
D) Temperature
E) Volume and temperature
7. A sample of nitrogen gas has a density of 1.25 g/L at STP. What is the molar mass of nitrogen?
A) 14.0 g/mol
B) 22.4 g/mol
C) 28.0 g/mol
D) 44.8 g/mol
E) 56.0 g/mol
8. If the molar mass of a gas is 32 g/mol, what is its density at STP?
A) 0.75 g/L
B) 1.25 g/L
C) 1.43 g/L
D) 2.14 g/L
E) 3.00 g/L
9. A gas has a density of 1.43 g/L at STP. What is the molar mass?
A) 16.0 g/mol
B) 22.4 g/mol
C) 32.0 g/mol
D) 36.0 g/mol
E) 44.0 g/mol
10. Which gas law can be rearranged to derive the density equation d = PM/RT?
A) Boyle’s Law
B) Charles’s Law
C) Ideal Gas Law
D) Dalton’s Law
E) Avogadro’s Law
11. The density of a gas is affected by all EXCEPT:
A) Temperature
B) Molar mass
C) Volume
D) Pressure
E) Color of gas
12. Which of the following conditions will result in the lowest gas density?
A) High pressure, low temperature
B) High pressure, high temperature
C) Low pressure, high temperature
D) Low pressure, low temperature
E) Standard pressure and temperature
13. Which of the following is the correct rearrangement to solve molar mass from density?
A) M = dRT/P
B) M = RTd/P
C) M = dP/RT
D) M = d/P
E) M = PRT/d
14. A gas has a molar mass of 20 g/mol and is at 2.00 atm and 273 K. What is its density? (R = 0.0821 L·atm/mol·K)
A) 1.20 g/L
B) 1.50 g/L
C) 2.00 g/L
D) 2.20 g/L
E) 2.40 g/L
15. Which of these gases would be expected to have the highest density under the same conditions?
A) CH₄
B) O₂
C) N₂
D) SO₂
E) CO
16. At what conditions is the gas density the highest?
A) Low pressure, high temperature
B) High pressure, low temperature
C) Low pressure, low temperature
D) High pressure, high temperature
E) STP
17. What volume will 4.40 g of CO₂ occupy at STP? (Molar mass = 44 g/mol)
A) 11.2 L
B) 22.4 L
C) 1.0 L
D) 2.24 L
E) 4.40 L
18. Which equation helps compare densities of two gases at the same T and P?
A) d₁/d₂ = T₁/T₂
B) d₁/d₂ = M₁/M₂
C) d₁/d₂ = P₁/P₂
D) d₁/d₂ = V₂/V₁
E) d₁/d₂ = n₂/n₁
19. The gas density increases if:
A) Temperature increases
B) Molar mass decreases
C) Pressure decreases
D) Temperature decreases
E) Gas is compressed into a larger volume
20. If the density of a gas is 2.50 g/L at STP, what is its molar mass?
A) 22.4 g/mol
B) 44.0 g/mol
C) 56.0 g/mol
D) 50.0 g/mol
E) 35.6 g/mol
Answers with Explanations
1. C) d = PM/RT
→ This is the rearranged ideal gas law including molar mass.
2. D) CO₂
→ CO₂ has the highest molar mass among the options, and density ∝ molar mass.
3. C) 1.96 g/L
→ d = 44.0 g/mol ÷ 22.4 L = 1.96 g/L
4. D) g/L
→ Grams per liter is the standard density unit for gases.
5. A) He
→ Helium has the lowest molar mass (4 g/mol), so lowest density.
6. C) Molar mass
→ Density is directly proportional to molar mass at constant T and P.
7. C) 28.0 g/mol
→ M = d × V = 1.25 g/L × 22.4 L = 28 g/mol
8. D) 1.43 g/L
→ d = 32 ÷ 22.4 = 1.43 g/L
9. C) 32.0 g/mol
→ M = 1.43 × 22.4 = 32.0 g/mol
10. C) Ideal Gas Law
→ PV = nRT rearranged leads to d = PM/RT
11. E) Color of gas
→ Density is a physical quantity, unrelated to color.
12. C) Low pressure, high temperature
→ Lowers the number of particles per volume.
13. A) M = dRT/P
→ Rearranged from d = PM/RT
14. C) 2.00 g/L
→ d = (2.00 atm × 20 g/mol) ÷ (0.0821 × 273) ≈ 2.00 g/L
15. D) SO₂
→ Highest molar mass = highest density.
16. B) High pressure, low temperature
→ Compresses gas particles closer, increasing density.
17. A) 11.2 L
→ 4.40 g ÷ 44 g/mol = 0.1 mol; 0.1 × 22.4 = 2.24 L
18. B) d₁/d₂ = M₁/M₂
→ At same T and P, density ∝ molar mass.
19. D) Temperature decreases
→ Decreased temperature = slower molecules = more density.
20. B) 44.0 g/mol
→ M = d × 22.4 = 2.50 × 22.4 = 56.0 g/mol
Practical Classroom Applications
- Gas density calculation worksheets for guided and independent practice.
- Ideal gas law review activities connecting pressure, temperature, and volume.
- Laboratory simulations involving gas samples and density measurements.
- Problem-solving exercises to strengthen quantitative chemistry skills.
- Preparation for chemistry exams and standardized tests.
- Identification of unknown gases using molar mass and density data.
- Real-world applications involving meteorology, aviation, and industrial gases.
- Interactive classroom activities using graphs, equations, and data analysis.
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