AAMC #3 Biology Passage Question

[EmpathMan]

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Hey all,

Question here from AAMC #3 Biology Passage III

"If a leak develops in the vacuum distillation apparatus, the boilings points of the two components of caraway seed will:"

A) Both increase (answer)
B) Both decrease
C) Both remain the same
D) Become more similar

I've read through their explanation, but I don't fully understand it. How does the surface pressure increase if a leak springs up?

Thanks for your time, appreciate any help!

 

[Like]

You have a vacuum, if the vacuum is broken, gas will rush into the apparatus. This gas will create surface pressure above the liquid and it will be harder to get the liquid to evaporate because there is already lots of gases floating above it and taking up space.
Made it so a kindergartner could understand...kinda. 😳

 

[szelda64]

You have a vacuum, if the vacuum is broken, gas will rush into the apparatus. This gas will create surface pressure above the liquid and it will be harder to get the liquid to evaporate because there is already lots of gases floating above it and taking up space.
Made it so a kindergartner could understand...kinda. 😳

The "gas" that enters the vacuum is the atmosphere pressure. Remember the concept of the vacuum is that it there is no existing atmosphere pressure inside the apparatus (like in physics, objects that move in a vacuum are not exposed to atmospheric air).

When there is a leak in the apparatus, it no longer acts as a vacuum as atmospheric air adds to the external pressure above the surface of the liquid. More pressure above the liquid makes it more difficult for liquid molecules to vaporize. This is why the boiling points of both liquids will increase.

 

[sakabato93]

Vapor pressure is inversely proportional to boiling point.

When there is a leak in the vacuum chamber, the vapor pressures of the respective liquids will decrease (according to Dalton's Law of Partial pressures -- mole fraction of each of the liquids will decrease when gas from an external source is introduced). If vapor pressure decreases, boiling point will increase. This is true for both substances since the vapor pressure of both substances is decreased by the external gas.