Equal volumes of carbon dioxide and a second gas weigh 32.00 g and 14.67 g respectively under the same experimental conditions. Which of the following is the unknown gas?

Question

Quizplus · Accepted Answer

According to the ideal gas law, PV = nRT, the molar mass of a gas can be calculated using the formula M = (mRT)/(PV). Since the volume and temperature are the same for both gases, their molar masses are proportional to their weights. Therefore, the molar mass ratio of carbon dioxide to the unknown gas is (32.00 g/mol)/(14.67 g/mol) = 2.18. The possible gases are He, O2, and Ne, and their molar masses are about 4 g/mol, 32 g/mol, and 20 g/mol, respectively. Only Ne has a molar mass close to the ratio calculated above, so the unknown gas must be Ne.

Equal Volumes of Carbon Dioxide and a Second Gas Weigh