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[BodybldgDoc]

got these two wrong on practice test.

1. Which of the following molecules is the LEAST soluble in water?
A. n-butanal
B. n-butanamine
C. diethylether
D. 2-propanone
E. butane
Correct answer=E But why? Is it because butane lacks hydrogen bonding in water?

2. Which of the following is most likely to be a gas at room temperature?
A. C2H6
B. C2H5OH
C. C2H6O
D. C6H6
E. None of the above
Correct answer=A Why A?

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[jackbauer!]

got these two wrong on practice test.

1. Which of the following molecules is the LEAST soluble in water?
A. n-butanal
B. n-butanamine
C. diethylether
D. 2-propanone
E. butane
Correct answer=E But why? Is it because butane lacks hydrogen bonding in water?

2. Which of the following is most likely to be a gas at room temperature?
A. C2H6
B. C2H5OH
C. C2H6O
D. C6H6
E. None of the above
Correct answer=A Why A?

1. remember, like dissolves like. water is a very polar molecule....butane is the most non-polar molecule listed. therefore, butane is least soluble.

2. Compounds that exist as gases at low T's (such as room T) have HIGH Vapor pressures.... a molecule vaporizes when it's vapor pressure equals the surrounding atmospheric T; therefore, the higher the Vapor P, the less heat that needs to be absorbed thus it has a lower B.P. Vapor pressure decreases with H-bonding/Polarity. You're looking for the molecule with the higest V pressure...so you're looking for the molecule with the least H-bonding/Polarity. That molecule is ethane, C6H6.

Hope that helps. jb!

 

[ananda]

Question 1 is E because butane possesses neither hydrogen bonding and is not a polar substance, therefore it will not be water soluble.

Question 2 is A because when you have any hydrocarbon molecule you have to keep the following in mind

Hydrocarbons with:
1-4 carbons = gas
5-16 carbons = liquid
17 and up = solid (wax)

Hope this helps!

 

[BodybldgDoc]

great thx guys