The density of air at STP is 1.285 g/L. Which of the following cannot be used to fill a balloon that will float in air at STP? CHA HF NH3 Ne NO
The Correct Answer and Explanation is:
Correct Answer: NO (Nitric oxide)
Explanation:
To determine which gas cannot be used to fill a balloon that will float in air at standard temperature and pressure (STP), we must compare the density of each gas to the density of air at STP (1.285 g/L). A balloon filled with a gas less dense than air will float, while one filled with a heavier (more dense) gas will sink.
We will use the molar mass of each gas and the ideal gas law relationship:
At STP, 1 mole of any ideal gas occupies 22.4 liters. So, the density of a gas at STP can be estimated as: Density (g/L)=Molar Mass (g/mol)22.4 L/mol\text{Density (g/L)} = \frac{\text{Molar Mass (g/mol)}}{22.4 \text{ L/mol}}Density (g/L)=22.4 L/molMolar Mass (g/mol)
Calculate Density for Each Gas:
- CH₄ (Methane)
Molar mass ≈ 12 + 4 = 16 g/mol
Density = 16 / 22.4 ≈ 0.714 g/L → lighter than air → floats - HF (Hydrogen fluoride)
Molar mass ≈ 1 + 19 = 20 g/mol
Density = 20 / 22.4 ≈ 0.893 g/L → lighter than air → floats - NH₃ (Ammonia)
Molar mass ≈ 14 + (3×1) = 17 g/mol
Density = 17 / 22.4 ≈ 0.759 g/L → lighter than air → floats - Ne (Neon)
Molar mass = 20.18 g/mol
Density = 20.18 / 22.4 ≈ 0.901 g/L → lighter than air → floats - NO (Nitric oxide)
Molar mass = 14 + 16 = 30 g/mol
Density = 30 / 22.4 ≈ 1.34 g/L → heavier than air → sinks
Conclusion:
Only NO has a density greater than air, so it cannot be used to fill a balloon that will float in air at STP.
✅ Answer: NO
