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# Explain Experiment 1

ACTSCI-8FABJO

A student is conducting an experiment to determine what factors affect the vapor pressure of methanol. The student is measuring the vapor pressure of methanol using a mercury manometer, as pictured below.

The experimental apparatus has an evacuated 1.0 liter bulb, into which the student injects a measured amount of methanol.

The methanol then vaporizes to a gas until the vapor pressure equilibrates with the liquid, by saturating the bulb volume with methanol vapor. The temperature of the methanol is controlled by placing it in a water bath.

The student measures the vapor pressure by determining the height of the mercury column after the methanol is injected.

Experiment 1 Results
The student first tried varying the volume of methanol injected into the bulb.

Experiment 2 Results
Next, the student tried varying the temperature of a fixed volume of methanol. The student made sure there was always methanol liquid in the glass bulb when the measurement of vapor pressure was taken.

Experiment 3 Results
Finally, the student tried measuring the vapor pressure of different substances, both with and without alcohol (-OH) groups, at 20° C.

Which of the following would be the BEST explanation for the results from Experiment 1?

A

The vapor pressure increases as the amount of liquid is added, as long as all the liquid vaporizes. Once there is liquid remaining in the container, the vapor pressure will remain constant.

B

The vapor pressure increases as the volume of methanol is added, as long as the volume is small compared to the volume of the container. Once the volume of methanol is large enough, then the space in the container is too small and the pressure stops increasing.

C

The volume of methanol added does not really affect the vapor pressure. Only the temperature changes the vapor pressure.

D

The vapor pressure changes due to the increased amount of methanol added. As you keep adding methanol, the vapor pressure should keep increasing.