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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 BEST describes the results from Experiment 3?


The heavier the molecule, the longer the carbon chain.


Adding an alcohol to the molecule offsets the longer carbon chain and minimizes the change to the vapor pressure.


The molar mass is the most important factor in determining the vapor pressure of a substance.


Lengthening the carbon chain or adding an alcohol to the molecule both reduce the vapor pressure.

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