3) A 255 mL round-bottom flask is weighed and found to have a mass of 114.85 R.

Question

3) A 255 mL round-bottom flask is weighed and found to have a mass of 114.85 R. A few milliliters of an asy. 83 vaporized liquid are added to the flask and the flask is immersed in a boiling water bath. All of the liquid vaporizés 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 these compounds could the liquid be? (Assume the ambient pressure is 1.0 atm.). Explain. A) C4H10 B) C3H7OH C) C2H6 D) C2H5OH E) C4H9OH

Explanation / Answer

Let's first consider options A and C which are only hydrocarbons: these are butane and ethane respectively. Each has very low boiling points -1 and -89. Hence they are in gaseous phase at ambient room temperature and pressure. Both cannot be re liquefied at room temperature. Hence option A and C are not the answer.

Option E is a butanol, with boiling point of 117. Hence it cannot be vaporized or boiled at water boiling point 100 . Thus it is not the answer.

Option B is a propanol with boiling point 97, which can be vaporized at 100 but practically to evaporate entirely all portion it will take time or it will be always in equilibrium in two phase (liquid and gas) at 100 due to close boiling point. Hence it is not the answer.

Option D is ethanol with boiling point of 78. As the boiling point of ethanol is significantly lower then boiling temperature of water, it can be vaporized at 100 completely and then re lquified after cooling. Hence answer is option D, C2H5OH.

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