Question

A student weighs an empty flask and stopper and finds the mass to be 53.256 g. She then adds about 5 mL of an unknown liquid and heats the flask in a boiling water bath at 98.8°C. After all the liquid is vaporized, she removes the flask from the bath, stoppers it, and lets it cool. After it is cool, she momen- tarily removes the stopper, then replaces it and weighs the flask and condensed vapor, obtaining a mass of 53.780 g. The volume of the flask is known to be 231.1 mL. The absolute atmospheric pressure in the laboratory that day is 728 mm Hg. a. What was the pressure of the vapor in the flask in atm?

Answer 1

a. The pressure in the flask open to the atmosphere during the vaporization of the unknown liquid is equal to the prevailing atmospheric pressure equivalent to 0.957734 atm

Step-by-step explanation:

The mass of the empty flask and stopper, m = 53.256 g

The volume of the unknown liquid she adds = 5 mL

The temperature of the water in which she heats up the flask = 98.8 °C = 371.95 K

The mass of the flask and the condensed vapor = 53.780 g

The volume of the flask, V = 231.1 mL

The atmospheric pressure, P = 728 mm Hg

a. We note that the student stoppers the flask after all the liquid has evaporated. Therefore, given that the flask was open to the atmospheric pressure as the liquid evaporates, the pressure of the vapor in the flask is equal to the prevailing atmospheric pressure, or 728 mmHg

Using a calculator, 728 mm Hg is equivalent to 0.957734 atm.