Self Assessment O-chem

[nabilesmail]

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Hey guys, quick question.

The passage pretty much is having a pot filled with cyclohexanol (BP 161) and trying to make cyclohexene and distill it (bp 83). They mention that the students try and keep the temp under 90.

The questions asks, why do the students try and keep the temp under 90.

I limited it to 2 answers.

1) To prevent cyclohexene from decomposing
2)to prevent unreacted cyclohexanol from distilling


I initially picked 2 but changed it to 1 because the Bp of cyclohexanol was 161, I didn't think boosting the temp to say 93 would boil it.

I also remember something in o-chem lab that a solution of 2 chemicals has a BP or Mp less than either. or something like that.

Can someone clarify this question?

 

[sciencebooks]

Hey guys, quick question.

The passage pretty much is having a pot filled with cyclohexanol (BP 161) and trying to make cyclohexene and distill it (bp 83). They mention that the students try and keep the temp under 90.

The questions asks, why do the students try and keep the temp under 90.

I limited it to 2 answers.

1) To prevent cyclohexene from decomposing
2)to prevent unreacted cyclohexanol from distilling


I initially picked 2 but changed it to 1 because the Bp of cyclohexanol was 161, I didn't think boosting the temp to say 93 would boil it.

I also remember something in o-chem lab that a solution of 2 chemicals has a BP or Mp less than either. or something like that.

Can someone clarify this question?

Would this relate to colligative properties? Like adding something more would increase the boiling point or decrease the melting point?

What was the answer, btw? Your reasoning is what I went with... Was it wrong?

 

[Sports Junky]

Hey guys, quick question.

The passage pretty much is having a pot filled with cyclohexanol (BP 161) and trying to make cyclohexene and distill it (bp 83). They mention that the students try and keep the temp under 90.

The questions asks, why do the students try and keep the temp under 90.

I limited it to 2 answers.

1) To prevent cyclohexene from decomposing
2)to prevent unreacted cyclohexanol from distilling


I initially picked 2 but changed it to 1 because the Bp of cyclohexanol was 161, I didn't think boosting the temp to say 93 would boil it.

I also remember something in o-chem lab that a solution of 2 chemicals has a BP or Mp less than either. or something like that.

Can someone clarify this question?

I just took the assessment as well, and my thought process was the exact same. 'The boiling point difference is large enough that this should not be a concern, therefore I will eliminate this answer'.

The explanation simply says that you're worrying about getting an impure product, but this should not be a problem unless the BP was raised > 160. Questions like this just make me want to go

In response to the MP/BP... I think your dealing with impurities in your product as a solid. If there are impurities, the lattice formation is impeded and so the melting point will be lower than the pure compound.

I'm not sure if this applies to liquids/gases as well, but if it does, then the answer choice they listed makes much more sense.

 

[nabilesmail]

I see I see, that applies to solid.

Hmm, weird question, seriously 160 is way higher than 90 lol

 

[sciencebooks]

I see I see, that applies to solid.

Hmm, weird question, seriously 160 is way higher than 90 lol

Hey, sorry, what was the answer? To prevent the boiling? Dumb.

*The question, not you.

 

[circulus vitios]

I figured that cyclohexene would be stable because six-carbon rings are generally stable. Some quick Googling shows that cyclohexene decomposes at 800 Kelvin. http://pubs.acs.org/doi/abs/10.1021/j100789a036

The difference in boiling points is pretty ridiculous, but it's more plausible than thermal decomposition of something that "seems" stable like cyclohexene.

 

[sciencebooks]

I figured that cyclohexene would be stable because six-carbon rings are generally stable. Some quick Googling shows that cyclohexene decomposes at 800 Kelvin. http://pubs.acs.org/doi/abs/10.1021/j100789a036

The difference in boiling points is pretty ridiculous, but it's more plausible than thermal decomposition of something that "seems" stable like cyclohexene.

I guess that make sense, but since it was cyclohexanOL, I tend to think of alcohols as more reactive than plain hydrocarbons but yeah, I guess this is one of those "best answer" questions everyone loves.