Question

Find the molar mass of the gas when $5.00$ liters of the gas at STP have a mass of $12.5$ grams?

• A. $12.5$ g$/$mol
• B. $25.0$ g$/$mol
• C. $47.5$ g$/$mol
• D. $56.0$ g$/$mol
• E. $125$ g$/$mol

Answer 1

The correct option is D $56.0$ g$/$mol

Molar mass is the mass of 1 mole of the gas.
At STP, 1 mole of a gas occupies a volume of 22.4 L.
5.00 liters of the gas at STP have a mass of 12.5 grams.
22.4 liters of the gas at STP have a mass of $12.5\times \frac{22.4}{5.00}=56.0$ grams. This is the molar mass of the gas.