# Determining the Pressure of Vapor in a Flask

## What was the pressure of the vapor in the flask in atm?

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

## Answer:

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

The student weighs the empty flask and stopper, finding the mass to be 53.256 g. Then, after adding about 5 mL of an unknown liquid and heating the flask in a boiling water bath at 98.8°C, all the liquid is vaporized. The mass of the flask and condensed vapor is measured to be 53.780 g, with a known flask volume of 231.1 mL.

Given an absolute atmospheric pressure of 728 mm Hg, the pressure of the vapor in the flask is equivalent to the prevailing atmospheric pressure, which is calculated to be 0.957734 atm. This determination is based on the understanding that the flask was open to the atmospheric pressure during the vaporization process.

**To calculate the pressure of the vapor in the flask using the ideal gas law equation:**

PV = nRT

Where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.

By converting the volume to liters, determining the number of moles based on the molar mass of the vapor, and applying the temperature in Kelvin, we can find the pressure of the vapor in the flask.