A 255 mL round-bottom flask is weighed and found to have a mass of 114.85 g. A few milliliters of an easily vaporized liquid are added to the flask and the flask is immersed in a boiling water bath. All of the liquid vaporizes at the boiling temperature of water, filling the flask with vapor. When all of the liquid has vaporized, the flask is removed from the bath, cooled, dried, and reweighed. The new mass of the flask and the condensed vapor is 115.23 g. Which of the following compounds could the liquid be? (Assume the ambient pressure is 1 atm.)

Question

Quizplus · Accepted Answer

The mass of the vaporized liquid is 115.23 g - 114.85 g = 0.38 g. Using the ideal gas law and the volume of the flask (0.255 L), we can calculate the molar mass of the vapor. At 1 atm and 373 K (boiling point of water), the molar mass is approximately 46 g/mol, which corresponds to ethanol (C₂H₅OH).

A 255 ML Round-Bottom Flask Is Weighed and Found to Have