1) The label has come off a cylinder of gas in your laboratory. You know only th

Question

1) The label has come off a cylinder of gas in your laboratory. You know only that one species of gas is contained in the cylinder, but you don't know whether it is oxygen, nitrogen or hydrogen. To find out, you evacuate a 5-liter flask, seal it, weight it and then let gas from the cylinder flow into it until the gauge pressure equals 1.00 atm. The flask is reweighed, and the mass of the added gas is found to be 13.0 g. Room temperature is 27 °C, and barometric [10] pressure is 1.00 atm. What is the gas?

Explanation / Answer

solution:

Assume ideal gas behavior: n = PV / RT

= [(1.00 + 1.00)atm / (0.08206 Latm/molK)]x[5L / 300K] = 0.406mol

MW = 13.0g / 0.406 mol = 32.0 g /mol      i.e Oxygen

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