Turn on thread page Beta
    • Thread Starter
    Offline

    14
    ReputationRep:
    Now this topic builds a real confusion. When do we use each?

    Like say xylene (bp 135 ) from water, why we prefer extraction here?

    Any tips?


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    Steam distillation is generally used to separate things that decompose at temperatures (often certain types of aromatics, like essential oils). You use steam to separate them from the fluid they were previously in, which is generally some mess of crap you've mashed up. For example, you use steam distillation to remove a mixture of carvone and limonene from a "solution" of water and mashed up caraway seeds. You pass steam through, and because the oils are in a mixture, and have a certain mole fraction, their vapour pressure is below their pure vapour pressure, so the temperate of the steam can volatilise them without heating them up by such a degree that they'll decompose.

    Extraction based on immiscibility is the more usual method, as it is far quicker and far simpler to perform. Also, steam canisters are terrifying.
    They are used for bulk immiscible liquids, where you can put the mixture into a separating funnel and simply let one phase run out of the bottom.
    Xylene is just a simple organic solvent, so it's far better to just use a a separating funnel. Also, the whole idea is usually that there is something you want in the organic solvent (for example, in the synthesis of a non-polar chemical, you'll use a non-polar solvent like xylene or toluene to dissolve it. Because a lot of reactants come as aqueous solutions, if you add a non-polar solvent to an aqueous mixture of a non-polar product, the product will dissolve preferentially in the non-polar solvent).

    Generally, you'll use steam distillation in the case of some extraction from a messy mixture of solids and liquids.

    But hey, I've only really done this twice, so take what I say with a pinch of salt.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Infraspecies)
    Steam distillation is generally used to separate things that decompose at temperatures (often certain types of aromatics, like essential oils). You use steam to separate them from the fluid they were previously in, which is generally some mess of crap you've mashed up. For example, you use steam distillation to remove a mixture of carvone and limonene from a "solution" of water and mashed up caraway seeds. You pass steam through, and because the oils are in a mixture, and have a certain mole fraction, their vapour pressure is below their pure vapour pressure, so the temperate of the steam can volatilise them without heating them up by such a degree that they'll decompose.

    Extraction based on immiscibility is the more usual method, as it is far quicker and far simpler to perform. Also, steam canisters are terrifying.
    They are used for bulk immiscible liquids, where you can put the mixture into a separating funnel and simply let one phase run out of the bottom.
    Xylene is just a simple organic solvent, so it's far better to just use a a separating funnel. Also, the whole idea is usually that there is something you want in the organic solvent (for example, in the synthesis of a non-polar chemical, you'll use a non-polar solvent like xylene or toluene to dissolve it. Because a lot of reactants come as aqueous solutions, if you add a non-polar solvent to an aqueous mixture of a non-polar product, the product will dissolve preferentially in the non-polar solvent).

    Generally, you'll use steam distillation in the case of some extraction from a messy mixture of solids and liquids.

    But hey, I've only really done this twice, so take what I say with a pinch of salt.
    I can see a brilliant, detailed explanation here. Many thanks!

    I will note those points. To add, can I say that it's even still better to use extraction since it does not require heat which might decompose our compound (although it will boil at a far lower bp )?

    Moreover, in my lab,I wonder why we used steam distillation to separate bromobenzene from water? Maybe because they were in small amounts?
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Infraspecies)
    Steam distillation is generally used to separate things that decompose at temperatures (often certain types of aromatics, like essential oils). You use steam to separate them from the fluid they were previously in, which is generally some mess of crap you've mashed up. For example, you use steam distillation to remove a mixture of carvone and limonene from a "solution" of water and mashed up caraway seeds. You pass steam through, and because the oils are in a mixture, and have a certain mole fraction, their vapour pressure is below their pure vapour pressure, so the temperate of the steam can volatilise them without heating them up by such a degree that they'll decompose.

    Extraction based on immiscibility is the more usual method, as it is far quicker and far simpler to perform. Also, steam canisters are terrifying.
    They are used for bulk immiscible liquids, where you can put the mixture into a separating funnel and simply let one phase run out of the bottom.
    Xylene is just a simple organic solvent, so it's far better to just use a a separating funnel. Also, the whole idea is usually that there is something you want in the organic solvent (for example, in the synthesis of a non-polar chemical, you'll use a non-polar solvent like xylene or toluene to dissolve it. Because a lot of reactants come as aqueous solutions, if you add a non-polar solvent to an aqueous mixture of a non-polar product, the product will dissolve preferentially in the non-polar solvent).

    Generally, you'll use steam distillation in the case of some extraction from a messy mixture of solids and liquids.

    But hey, I've only really done this twice, so take what I say with a pinch of salt.
    Check those questions (they are from past papers I got):

    1) Separate dichloromethane and water: Extraction
    2) Best method to separate hexane from acetone: Steam distillation (Why?)
    3) Separating bromobenzene from water: Steam distillation
    4) Isolate eugenol from natural sources: Extraction

    I truly would have answered just the opposite haha :/
    Offline

    16
    ReputationRep:
    (Original post by Daniel Atieh)
    Check those questions (they are from past papers I got):

    1) Separate dichloromethane and water: Extraction
    2) Best method to separate hexane from acetone: Steam distillation (Why?)
    3) Separating bromobenzene from water: Steam distillation
    4) Isolate eugenol from natural sources: Extraction

    I truly would have answered just the opposite haha :/
    1) DCM and water are immiscible, so can be separated with a separating funnel easily.

    2) Acetone and hexane are miscible, so a separating funnel would be useless (there's only 1 phase). Hence, you'd need to distil the solution. Unfortunately, they have very similar boiling points, so they form an azeotrope.
    So, you utilise the fact that hexane has a different vapour pressure, and is separable by steam distillation from the solution.

    3) I would separate bromobenzene from water with a separating funnel.

    4) I would think you'd use steam distillation to remove eugenol from natural sources, but I'm not sure.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Infraspecies)
    1) DCM and water are immiscible, so can be separated with a separating funnel easily.

    2) Acetone and hexane are miscible, so a separating funnel would be useless (there's only 1 phase). Hence, you'd need to distil the solution. Unfortunately, they have very similar boiling points, so they form an azeotrope.
    So, you utilise the fact that hexane has a different vapour pressure, and is separable by steam distillation from the solution.

    3) I would separate bromobenzene from water with a separating funnel.

    4) I would think you'd use steam distillation to remove eugenol from natural sources, but I'm not sure.


    Thank you once again

    1) Well. I will not even need to add any solvent here. Just direct separation.
    2) Are you sure they are miscible? Acetone is polar while hexane is non-polar (?)
    But even if they are miscible, can't I add a solvent which dissolves one more than the other and get what I need?
    3) I am confused here :/ Maybe because the amount is usually too small to be accurately separated using separatory funnel?
    4) I think by isolate they mean the solid liquid extraction? and then after that we can do steam distillation?
    Offline

    16
    ReputationRep:
    (Original post by Daniel Atieh)
    Thank you once again

    1) Well. I will not even need to add any solvent here. Just direct separation.
    2) Are you sure they are miscible? Acetone is polar while hexane is non-polar (?)
    But even if they are miscible, can't I add a solvent which dissolves one more than the other and get what I need?
    3) I am confused here :/ Maybe because the amount is usually too small to be accurately separated using separatory funnel?
    4) I think by isolate they mean the solid liquid extraction? and then after that we can do steam distillation?
    2) I think hexane and acetone are miscible, yes. I'm sure it's a close thing, for hexane isn't in acetonitrile or acetic acid, but hexane and acetone do.

    As for an intermediary, I'm not sure. A lot of things, as you can see from hexane, are miscible with acetone. Attempting to get two phases may be hard.
    https://www.erowid.org/archive/rhodi...iscibility.pdf

    3) Maybe, I don't really understand the question.

    4) Generally you just to steam distillation to remove the compounds directly from the congealed mess in your flask.
    • Thread Starter
    Offline

    14
    ReputationRep:
    (Original post by Infraspecies)
    2) I think hexane and acetone are miscible, yes. I'm sure it's a close thing, for hexane isn't in acetonitrile or acetic acid, but hexane and acetone do.

    As for an intermediary, I'm not sure. A lot of things, as you can see from hexane, are miscible with acetone. Attempting to get two phases may be hard.
    https://www.erowid.org/archive/rhodi...iscibility.pdf

    3) Maybe, I don't really understand the question.

    4) Generally you just to steam distillation to remove the compounds directly from the congealed mess in your flask.
    I highly appreciate your efforts. Thanks a bunch!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 10, 2015

2,217

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should predicted grades be removed from the uni application process

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.