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OCR Chemistry F322~ 4th June 2013~ AS Chemistry Watch

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    Easy A= 79
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    How are you guys revising? I can't seem to get anything to stick in my head Im so screwed
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    (Original post by Jimmy20002012)
    There was thus question I was doing today, and it said it made the ester of Propyl ethanol and enthanoic acid was used. You were meant to find out the alcohol and conditions needed for the reaction, I bought the alcohol would be propanol, but they don't accept this as it is propan-1-ol, why and how could you have known this?


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    if it was propan-2-ol, when you draw the product formed when its reacted with ethanoic acid, propyl ethanoate isn't made because the OH is on a different carbon therefore the propyl bit isnt actually propyl. draw it out and you'll see what I mean - the structures slightly different.
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    (Original post by 344302)
    I'm having trouble with this too! I got the theoretical amount of hydrogen but I don't understand how they found the actual amount of hydrogen?


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    200 Tonnes of Methane = 200,000,000g of Methane
    Moles=200,000,000/16
    =12500000 moles of Methane
    3 Moles of Hydrogen in the equation, therefore
    12500000 X 3=37500000 moles of hydrogen [THEORETICAL]

    In the question it says 68.4 tonnes of Hydorgen is produced
    68.4 tonnes = 68400000g of Hydrogen
    Moles= 68400000/2
    =34200000 moles of Hydrogen [ACTUAL]

    % Yield= (34200000/37500000) X 100
    =91.2%
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    (Original post by needtosucceed=))
    if it was propan-2-ol, when you draw the product formed when its reacted with ethanoic acid, propyl ethanoate isn't made because the OH is on a different carbon therefore the propyl bit isnt actually propyl. draw it out and you'll see what I mean - the structures slightly different.
    Why not propanol? Or is that because its too vague?


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    (Original post by Jimmy20002012)
    There was thus question I was doing today, and it said it made the ester of Propyl ethanol and enthanoic acid was used. You were meant to find out the alcohol and conditions needed for the reaction, I bought the alcohol would be propanol, but they don't accept this as it is propan-1-ol, why and how could you have known this?


    Posted from TSR Mobile
    if it was propan-2-ol the ester would have been 2-methyl ethyl ethanoate because having the OH group on the second carbon creates a branch on the ester... so it has to be propan-1-ol
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    hi guys. need help
    june 2010
    6d c(i)

    http://www.ocr.org.uk/Images/65130-q...-resources.pdf

    I am coming out with a negative value of -5.68 × 10
    7

    answer is postitive, anyone spot where i am going wrong.

    i did : -909/4 = 227.25
    i then -227.25 x2.50x10*5.. thanks
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    (Original post by Jimmy20002012)
    Why not propanol? Or is that because its too vague?


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    yea its too vague. you have to put a number to show where the OH is. the only place you dont put it is on methanol or ethanol (unless theres 2 OH groups on ethanol then u have to)
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    (Original post by scorpio22)
    hi guys. need help
    june 2010
    6d c(i)

    http://www.ocr.org.uk/Images/65130-q...-resources.pdf

    I am coming out with a negative value of -5.68 × 10
    7

    answer is postitive, anyone spot where i am going wrong.

    i did : -909/4 = 227.25
    i then -227.25 x2.50x10*5.. thanks
    Look at the 866th post on page 44, I already answered how to do this question. They asked how much energy is RELEASED. So negative not needed
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    (Original post by scorpio22)
    hi guys. need help
    june 2010
    6d c(i)

    http://www.ocr.org.uk/Images/65130-q...-resources.pdf

    I am coming out with a negative value of -5.68 × 10
    7

    answer is postitive, anyone spot where i am going wrong.

    i did : -909/4 = 227.25
    i then -227.25 x2.50x10*5.. thanks
    you never give any signs for energy. -ve or +ve signs are only given for enthalpy changes. energys always positive
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    Just thought i'd say that i would advise people to draw the hess's law cycle rather than remembering the equations of products-reactants/reactants-products just because it is SO easy to make a mistake when you try to remember it. I never bothered to learn it properly the first time i did it last year and it was always hit or miss as to whether i got the values right. Now I can do the cycle it's much easier to work out enthalpy changes and even if you get it wrong it's much easier for examiners to award marks from a cycle rather than just a long list of calculations that aren't clear. Just a tip !
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    (Original post by needtosucceed=))
    yea its too vague. you have to put a number to show where the OH is. the only place you dont put it is on methanol or ethanol (unless theres 2 OH groups on ethanol then u have to)
    Then you would have Ethan-2,2-ol? So if you used pentan-2-ol in that question you would get 2-pentyl ethanoate?


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    Thankyou.
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    (Original post by scorpio22)
    hi guys. need help
    june 2010
    6d c(i)

    http://www.ocr.org.uk/Images/65130-q...-resources.pdf

    I am coming out with a negative value of -5.68 × 10
    7

    answer is postitive, anyone spot where i am going wrong.

    i did : -909/4 = 227.25
    i then -227.25 x2.50x10*5.. thanks
    From the equaton we know that the production of 4 Moles of NO gives -909kJ mol-1
    4NO=-909
    NO=-909/4
    250000NO=-56812500
    The minus sign shows that the reaction is exothermic and the question asks how much energy is released, so just get rid of the minus sign leaving the answer as 56812500kJ
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    (Original post by Jimmy20002012)
    Then you would have Ethan-2,2-ol? So if you used pentan-2-ol in that question you would get 2-pentyl ethanoate?


    Posted from TSR Mobile
    if there were 2 OH on the same carbon then it would be ethane-1,1-diol. It can't possibly be -2,2- because the numbers are put in to give the lowest possible value. If the OH were on different carbons it would be ethane-1,2-diol. No you'd get something like butyl methyl ethanoate. don't worry about that though it won't come up, they only ever have esterification reactions based on the OH group being on the 1st carbon.
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    (Original post by supernova99)
    Just thought i'd say that i would advise people to draw the hess's law cycle rather than remembering the equations of products-reactants/reactants-products just because it is SO easy to make a mistake when you try to remember it. I never bothered to learn it properly the first time i did it last year and it was always hit or miss as to whether i got the values right. Now I can do the cycle it's much easier to work out enthalpy changes and even if you get it wrong it's much easier for examiners to award marks from a cycle rather than just a long list of calculations that aren't clear. Just a tip !
    this is so true, I always use the cycles, you (generally) should always get the answer right if you've used the cycle
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    Guys I'm really struggling with the enthalpy arrow diagram thing .. I just don't understand what it is ! Any easy explanations ? Plus any tips for the exam ? Xx anybody want to play the ask each other questions game ? Haha


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    I've nearly finished rewriting all of my notes for the second time! Starting past papers tonight!.. Cutting it fine haha


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    (Original post by ladybug.hugsxoxo)
    Guys I'm really struggling with the enthalpy arrow diagram thing .. I just don't understand what it is ! Any easy explanations ? Plus any tips for the exam ? Xx anybody want to play the ask each other questions game ? Haha


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    The Hess Cycles??
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    (Original post by supernova99)
    Just thought i'd say that i would advise people to draw the hess's law cycle rather than remembering the equations of products-reactants/reactants-products just because it is SO easy to make a mistake when you try to remember it. I never bothered to learn it properly the first time i did it last year and it was always hit or miss as to whether i got the values right. Now I can do the cycle it's much easier to work out enthalpy changes and even if you get it wrong it's much easier for examiners to award marks from a cycle rather than just a long list of calculations that aren't clear. Just a tip !
    I dont know how to draw the cycle
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    (Original post by greenmind)
    Hmm.. okay so the fractions are basically the end products then, with each fraction having similar boiling points, which can be distilled further to make purer hydrocarbons... right?
    Umm, that sounds about right
 
 
 
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