Question

Which of the following gases has the highest density at STP?

• A. \( \text{CO}_2 \)
• B. \( \text{O}_2 \)
• C. \( \text{N}_2 \)
• D. \( \text{CH}_4 \)

Hint:

Remember: At STP, the density of a gas is directly proportional to its molar mass. Higher molar mass means higher density.

Answer 1

The Correct Option is A

Step 1: Density Formula for Gas at STP
Density (\( \rho \)) of a gas at Standard Temperature and Pressure (STP) is calculated as:\[\rho = \frac{\text{Molar mass}}{\text{Molar volume at STP}}\]The molar volume of any ideal gas at STP is approximately \( 22.4 \, \text{L/mol} \).
Step 2: Compare Molar Masses
- \( \text{CO}_2 \) Molar mass: \( 44 \, \text{g/mol} \) (\( 12 + 2 \times 16 \)),
- \( \text{O}_2 \) Molar mass: \( 32 \, \text{g/mol} \) (\( 2 \times 16 \)),
- \( \text{N}_2 \) Molar mass: \( 28 \, \text{g/mol} \) (\( 2 \times 14 \)),
- \( \text{CH}_4 \) Molar mass: \( 16 \, \text{g/mol} \) (\( 12 + 4 \times 1 \)).
Step 3: Identify Gas with Highest Density
At STP, density is directly proportional to molar mass. \( \text{CO}_2 \) has the highest molar mass, therefore it has the highest density at STP.Answer: \( \text{CO}_2 \) exhibits the highest density at STP. Option (1) is the correct answer.