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Thread: esters - lab due tomorrow - HELP!

  1. #1 esters - lab due tomorrow - HELP! 
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    alright so in chem we did a lab in which we created scents by synthesizing esters with alcohols and carboxylic acids and it was cool and all but now i'm stuck on something in my write up...

    esters are supposedly volatile by nature because even though they are polar molecules because of the double bonded oxygen, they are unable to hydrogen bond intermolecularly due to the lack of an OH group. they are also supposedly very soluable because once placed in water, they are able to form stronger intermolecular bonds with h2o atoms than with themselves. in the lab, the esters produced smelled STRONGER AFTER they were placed in cold water, which to me makes no sense because after being placed in water they would be less volatile

    help?


    kate
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    properties of an ester: C=O and C-O bonds make a ester a polar substance. however the lack of hydrogen bonding means that the ester has a much loweer boiling point than acids or alkanols of the same molecular wieghtm therefore they are also much less soluable in water.
    The use of refluxing :
    the pocess of heating a reaction mixture in a vessel witha cooliing condenser attached in order to prevent loss of any volatile reactant or product.

    It allows the reaction to be brought about a higher temperature than would other wise be possible. the alt. of performing the reaction in a closed vessel could lead to a dangerous build of pressure = explosion!!!


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  4. #3  
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    that makes sense... but we heated the alcohol, acid, and catalyst in a hot water bath for about 15 minutes, observed smell, then cooled it and observed again. wouldnt the ester become less volatile once placed in water, and therefore not smell as strong?
    kate
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  5. #4  
    Forum Freshman lewisy's Avatar
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    NO, coz you have to let it settle, when observing it you should see a effect, similar to that when you look at petrol or gas (depending where ur from) on the road, you see the swirls of the rainbow, but instead its in a clear solution and the rainbow is more like a different shade of the solution it is in. when you heat it up in the bath youre allowing for the particles to have more enregy, based on the partical theory. This allows more reactions to occur within the beaker hence for a great sence of smell.
    "Esters may undergo hydrolysis - the breakdown of an ester by water. This process can be catalyzed both by acids and bases. The base-catalyzed process is called saponification. The hydrolysis yields an alcohol and a carboxylic acid or its carboxylate salt.
    Esters also react if heated with primary or secondary amines, producing amides wikipedia"
    Think of water as a third party, it there but it doesn't support the backbone of the business, that is the smell.
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  6. #5  
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    sorry if i'm being a bit dense, i've been workin on this damn thing since 4pm on little sleep (it was a good thanksgiving weekend)... but it stills eems as tho the esters should have smelled stronger after being heated and smelled wekaer after being cooled, when during the lab, they smelled stronger after being cooled. also, did see the "rainbow effect", so we must have done something right
    kate
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  7. #6  
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    ps. really really appreciate the help, i cant find info on this anywhere
    kate
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  8. #7  
    Forum Freshman lewisy's Avatar
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    try this concept.
    The reaction has already taken place, the smell is aready in existance, cooling it down won't effect the smell since it has already been produced. As the strength dies down, probably because the reaction's energy has be used up the smell dies. But not cooling it dowing. Basic chem says that cooling down the reaction causes the reaction to last longer. eg place a glow stick in the fridge after snaping it and it will last longer (glowing) insidde than being outside. this is because temperature outside will speed the reaction up.
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  9. #8  
    Forum Freshman lewisy's Avatar
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    me helping you helps me understand. if that makes sence
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  10. #9  
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    haha yeah i love tutoring people for the purely selfish reason of it giving me better grades. the glow stick concept makes alot more sense, my brain is still grasping a bit though
    kate
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  11. #10  
    Forum Freshman lewisy's Avatar
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    best way to accomplish something that you have been tryin hours on is to take a break come back a look at it from a different poin t of view.
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  12. #11  
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    i've done the break and come back... one too many times haha i tend to get easily distracted. but i'm also getting frustrated because all the resources i'm finding are either too simple or too complicated, and i still havent found an answer that satisfies me, because although it makes sense that cooling the products of the reaction would prolong the smell, i don't see why it would make it smell stronger. if a volatile substance is heated, the molecules would be more energetic and more volatile, and smell stronger, and also, i've read that esters are able to bond strongly with water, so that would make them even less volatile... my brain hurts
    kate
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  13. #12  
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    a haaaa i found it
    kate
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  14. #13  
    Forum Freshman lewisy's Avatar
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    the answer is?
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  15. #14  
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    on small scale ester synthesis experiments, there is often not alot of product formed, and the strong acidic smell can overpower the smell of the ester.... since esters are insoluable in water, they will settle on top (the gasoline-rainbow effect) while the excess reactants dissolve in the water, getting rid of the acid smell and making the ester's smell clearer
    kate
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  16. #15  
    Forum Freshman lewisy's Avatar
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    since u found the answer go sleep, and if need be, take a red bull before the exam only one.
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  17. #16  
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    so nnew question... why wont esters dissolve in water, seeing as they are polar
    kate
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  18. #17  
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    haha sleep is no where in sight, unfortunately
    kate
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  19. #18  
    Forum Freshman lewisy's Avatar
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    oil and water don't mix... think about it...
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  20. #19  
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    yeah that was just a flat out dumb question
    kate
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  21. #20  
    Forum Freshman lewisy's Avatar
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    not enough sleep :wink:
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  22. #21  
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    well i won't deny that, but its kind of due at 9 am, so staying up is the only option here
    kate
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  23. #22  
    Forum Freshman lewisy's Avatar
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    what do uhave to do next
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  24. #23  
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    make sure my intro makes sense... discuss the results... nice little conclusion... then my nice comfy bed
    kate
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  25. #24  
    Forum Freshman lewisy's Avatar
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    if you find a problem, don't leave it out of ur report, write then say how u would have fixed it, teaches like that crap, but make sure u state it in A separate section
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  26. #25  
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    course, i love making mistakes in labs, gives you more to talk about
    kate
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  27. #26  
    Forum Freshman lewisy's Avatar
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    just make sure the mistakes are not the chemistry between the sheets of your bed
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  28. #27  
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    oh honey that a whoooole different ballgame
    kate
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  29. #28  
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    good luck, hope u go well then... post how u went :wink:
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  30. #29  
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    i'm not gonna lie... i don't understand your last post at all. like at ALL
    kate
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  31. #30  
    Forum Freshman lewisy's Avatar
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    translation: good luck for your lab prac assessment thing, and post your mark - just to c how u went -sorry
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  32. #31  
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    oh.... k haha thanks
    kate
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  33. #32  
    Forum Freshman lewisy's Avatar
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    better go to sleep otherwise u'll stuff your prac
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  34. #33  
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    so... i finished everything and got to class and half the students didnt even do it... so my teacher just moved the damned due date to friday. and what'd ya mean by prac?
    kate
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  35. #34  
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    a experiement that is assessable
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