At NTP (0 °C and 1 atm), 2 litres of nitrogen gas (N2) are contained in a vessel. Approximately how many grams does this amount of nitrogen weigh?

Introduction / Context:
NTP (normal temperature and pressure) conditions simplify gas calculations. At NTP (taken here as 0 °C and 1 atm), one mole of an ideal gas occupies about 22.4 litres. This problem checks understanding of molar volume and mass–mole conversions for nitrogen, N2, which is common in chemical engineering material balance work.

Given Data / Assumptions:

• NTP ≈ 0 °C (273 K) and 1 atm total pressure.
• Molar volume at NTP ≈ 22.4 L per mol (ideal gas approximation).
• Molar mass of N2 = 28 g per mol.
• Gas behaves ideally; container effects are negligible.

Concept / Approach:
The number of moles is computed using the molar volume at NTP. Once moles are known, multiply by the molar mass to obtain mass in grams. The linear proportionality between volume and moles at fixed T and P is the key idea.

Step-by-Step Solution:

Verification / Alternative check:
As a sense check, 22.4 L of N2 would weigh 28 g at NTP; therefore 2 L is about 2/22.4 of 28 g, which is 2.5 g. The ratio method confirms the calculation without a calculator.

Why Other Options Are Wrong:

• 14 and 28 g: These are the masses for 0.5 mol and 1 mol of N2, respectively, not for 2 L.
• 1.25 g: This would correspond to 1 L of N2 at NTP (half of 2.5 g).

Common Pitfalls:
Using the molar mass of atomic nitrogen (14 g per mol) instead of diatomic nitrogen (28 g per mol), or using the wrong molar volume (e.g., 24.0 L per mol at 25 °C) can lead to errors.

Final Answer:
2.5