Dry air at STP contains approximately what mole percent of Argon?

Dry air at STP contains approximately what mole percent of Argon?

• A. Argon
• B. Helium
• C. Neon
• D. Krypton

Answer: (A)

Air is a mixture of gases with specific mole fractions, and mole percent just means those fractions times 100. In dry air, argon is a noble gas present in trace amounts, but it is the largest among the noble gases in the atmosphere. Its mole fraction is about 0.00934, which corresponds to roughly 0.93% of the air. The other noble gases—helium, neon, krypton—occur at far smaller levels, typically only a few parts per million or less, so their mole percentages are well below 0.1%. Therefore, the approximate mole percent of argon in dry air is about 0.9–1%, with 0.93% being a good textbook figure.

Air is a mixture of gases with specific mole fractions, and mole percent just means those fractions times 100. In dry air, argon is a noble gas present in trace amounts, but it is the largest among the noble gases in the atmosphere. Its mole fraction is about 0.00934, which corresponds to roughly 0.93% of the air. The other noble gases—helium, neon, krypton—occur at far smaller levels, typically only a few parts per million or less, so their mole percentages are well below 0.1%. Therefore, the approximate mole percent of argon in dry air is about 0.9–1%, with 0.93% being a good textbook figure.