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    (Original post by SuperHuman98)
    watched the videos for fractional distillation I sitll dont understand the method
    Ok....

    You are using distillation to separate two more more chemicals that have differing boiling points. By heating them up carefully the most volatile (the lowest boiling point), will evaporate (turn into a gas) and rise up the tube. This gas can then be passed along a condenser (glass tube with water running around it) where it is cold and hence it will condense (gas -> liquid) and you can collect this liquid while leaving the other one behind.

    The video just shows separation of two liquids, if it was more than two then you could use fractional distillation which is a larger version but has lots of condensers coming off so you can separate more than one fraction (chemical) at a time, an example of this would be fractional distillation of crude oil which you probably studied at GCSE.

    Alex
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    Just wondering....For all acid catalyzed reactions can we just say it is H2SO4 for all of them or are there some where we HAVE to have Phosphoric Acid?
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    (Original post by AdamWallisjr)
    Just wondering....For all acid catalyzed reactions can we just say it is H2SO4 for all of them or are there some where we HAVE to have Phosphoric Acid?
    Generally both work as long as it's used as a catalyst
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    (Original post by rosemondtan)
    Generally both work as long as it's used as a catalyst
    Ok, Thank you
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    (Original post by AdamWallisjr)
    Ok, Thank you
    Remember that it has to be concentrated acid as well!!


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    Can someone explain what exactly the practical 'Distillation of a product from a reaction' is?
    Thanks!
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    Lets see how much aqa f**k up in this exam. Physics: cross out q9, biology they don't know ATP hydrolysis. I just wonder what they'll do...
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    (Original post by jessnrm)
    It says explain... so maybe a sufficient amount of detailed is required. Quite hard to tell without an indication of how many marks it would be.

    And yes I think you're just about correct with reflux with carboxylic acid and distillation with aldehydes.
    And yes again - you may have to explain them respectively;

    So the reason why you want to DISTIL aldehydes is because it can be easily oxidised to carboxylic acid if it is in excess. Using a condenser as a make-do distillation column allows the aldehyde produced to condense into a liquid and be collected - in a sense it allows equilibrium to shift to the right since continuously removing the product prevents any of the produced aldehyde to quickly oxidise into carboxylic acid. This is a PARTIAL oxidation of alcohols.

    Reflux however is basically allowing the product to condense and drop back down in solution. So excess aldehyde is still present for full oxidation. It's quite a different set-up to a distillation set-up. (Condenser is at the top to allow the condenses liquid to drop down back into flask).
    So anyways, heating the alcohol solution under REFLUX allows FULL OXIDATION to the carboxylic acid.

    And you might need to know your Test for Functional Groups as well - just for the safe measure.
    The test for aldehydes can either be using Tollen's re-agent / Benedict's / Fehling's
    The test for carboxylic acids is basically adding Sodium Hydrogden Carbonate (look it up - i'm not too sure) which will fizz to produce Carbon Dioxide, and if you bubble it through limewater it should turn cloudy.

    So if you oxidise the alcohol using an oxidising agent (e.g potassium (IV) dichromate) and it tests positive for aldehydes - then it's an aldehyde.
    Oxidise an alcohol under reflux using the same oxidising agent, and it tests positive for carboxylic acids - then it's a Carboxylic acid.

    Hope this helps
    Thanks a lot!
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    We never did cyclohexene practical
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    (Original post by metrize)
    We never did cyclohexene practical
    Same here, all we need to know is how to get alkenes from alcohols.

    This is what I watched: https://www.youtube.com/watch?v=1mDVFH5znfA

    Its quite simple so don't worry...
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    In specimen papers for organic, was it just the distillation experiment that came up?
    Cause I doubt it'd come up again
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    Does anyone have a link to the two secure specimen papers?
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    (Original post by haes)
    Does anyone have a link to the two secure specimen papers?
    Here is 1 paper: http://www.aqa.org.uk/subjects/scien...ment-resources
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    Also does anyone have like a general rule for how to answer "how many isomers does ___ have?"
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    Do we need to know mechansims for hydration and dehydration
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    (Original post by metrize)
    Do we need to know mechansims for hydration and dehydration
    all mechanisms so yeah
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    The equation for the hydrogenation of ethyne is C2H2 + 2H2 --> C2H6.The experimental yield is 65%.What is the mass I'm grads of ethane that can be produced from 16.20g of hydrogen.

    The answer is 79.98g, please explain thanks
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    Is atomic structure on the paper? Also do we need to know equations for tollens reagent and fehlings solution?
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    (Original post by student_1999)
    The equation for the hydrogenation of ethyne is C2H2 + 2H2 --> C2H6.The experimental yield is 65%.What is the mass I'm grads of ethane that can be produced from 16.20g of hydrogen.

    The answer is 79.98g, please explain thanks
    First find the moles, which is 8.1.

    Its a 2 to 1 ratio so 4.05 moles of c2h6 is made

    Therefore the mass made is 121.5g, however we only get 65% due to the yield, and so 78.98g (to 2dp) is forned
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    (Original post by shivanisinha1998)
    Is atomic structure on the paper? Also do we need to know equations for tollens reagent and fehlings solution?
    no and I'm not sure, what kinda equations?
 
 
 
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