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

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    (Original post by Jacksgap)
    How many UMS mark in an A just for F322 guys???
    120/150
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    (Original post by Jacksgap)
    Hi could u briefly explain how to do thse kinda questions... it even cam up in Jan 2012 paper Question 3 b ii

    THANK YOUU
    The one on the January 2012 paper is waaaaaaaaayyyyyy easier. On the jan 2012 one you just have to look for the reaction thats occuring and but the deltaH value in then add them up. On the Jan 2012 one you see the equation goes from 2Ca + 2HCl --->CaCl2+H2 and the C and 1.5O2 remains the same. This value is given as -168 in the table. You just do this all the way round then add them up.
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    (Original post by GeneralOJB)
    Attachment 221967

    Hope this helps?
    Okay, I can see it now, thank you!!! I was drawing the Hess's cycles, but I was getting confused with how to put those fractions together in a cycle that made sense - I didn't think of subtracting the values instead of adding them around the cycle
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    how can you tell how many isomers lets say CH3CH2CH2CH3, and tell me how you can find it out.
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    June 2011, question 3ci about dynamic equilibrium. How would you know that the forward reaction was faster to start with?

    The question is:

    A research chemist investigates the reaction between nitrogen and oxygen. She mixes nitrogen and oxygen gases in a sealed container.
    She then heats the container at a constant temperature for one day until the gases reach adynamic equilibrium.


    1. (i) Explain, in terms of the rate of the forward reaction and the rate of the backward reaction,how the mixture of N2(g) and O2(g) reaches a dynamic equilibrium containing N2(g),O2(g) and NO(g).



    And the answer's that the forward reaction slows down and the backward reaction speeds up. But how would you know which way round it was?

    Thanks.
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    hi guys does anyone know approx what we'll need to get 130 ums in the paper (i know they change every year- but an approx value to put my mind to rest (or most probably make me lose my hair
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    (Original post by Anonymous1717)
    June 2011, question 3ci about dynamic equilibrium. How would you know that the forward reaction was faster to start with?

    The question is:

    A research chemist investigates the reaction between nitrogen and oxygen. She mixes nitrogen and oxygen gases in a sealed container.
    She then heats the container at a constant temperature for one day until the gases reach adynamic equilibrium.


    1. (i) Explain, in terms of the rate of the forward reaction and the rate of the backward reaction,how the mixture of N2(g) and O2(g) reaches a dynamic equilibrium containing N2(g),O2(g) and NO(g).



    And the answer's that the forward reaction slows down and the backward reaction speeds up. But how would you know which way round it was?

    Thanks.
    You start off with the reactants.
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    (Original post by Anonymous1717)
    June 2011, question 3ci about dynamic equilibrium. How would you know that the forward reaction was faster to start with?

    The question is:

    A research chemist investigates the reaction between nitrogen and oxygen. She mixes nitrogen and oxygen gases in a sealed container.
    She then heats the container at a constant temperature for one day until the gases reach adynamic equilibrium.


    1. (i) Explain, in terms of the rate of the forward reaction and the rate of the backward reaction,how the mixture of N2(g) and O2(g) reaches a dynamic equilibrium containing N2(g),O2(g) and NO(g).



    And the answer's that the forward reaction slows down and the backward reaction speeds up. But how would you know which way round it was?

    Thanks.
    If you look at that question, you will notice that it starts with the equation for that reaction with the delta H value. This should help.
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    In nucleophilic substitution, do I have to show the intermediate?
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    determine the possible structural formulae and/or
    stereoisomers of an organic molecule, given its
    molecular formula;
    E.g – Pentane – C5H12

    how do you do this plzzz some1 tell me.
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    whats the steroisomer for CH2CHCH2CH2CH3?
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    (Original post by chigyy)
    In nucleophilic substitution, do I have to show the intermediate?
    no you don't you can do it "all in one" step
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    (Original post by Sum786)
    whats the steroisomer for CH2CHCH2CH2CH3?
    Someone correct me if I'm wrong but
    I just drew it out and I don't think you can have stereoisomers for that because one carbon on the C=C double bond is attached to two hydrogens.
    But it is a structural isomer of CH3CH=CHCH2CH3 which can have steroisomers?
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    (Original post by junaid_k17)
    determine the possible structural formulae and/or
    stereoisomers of an organic molecule, given its
    molecular formula;
    E.g – Pentane – C5H12

    how do you do this plzzz some1 tell me.
    you can only have steroisomers with alkenes.
    for pentane, just draw out all the possible ways the carbons can be arranged - straight chained and branched.
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    On this question, I can either implement eqns 1&3 or eqns 2&3 into my cycle perfectly - but then I'm getting stuck with the remaining eqn as it won't fit to make a closed loop! Do you have any pointers?
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    http://www.thestudentroom.co.uk/atta...6&d=1357952433
    http://www.ocr.org.uk/Images/135164-...urces-june.pdf

    Hi can someone please explain how you get the answer for 4eii? It's the Hess's cycle one?
    I'm just thinking shouldn't it be a negative value because its reacting with oxygen?

    Thanks
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    (Original post by junaid_k17)
    determine the possible structural formulae and/or
    stereoisomers of an organic molecule, given its
    molecular formula;
    E.g – Pentane – C5H12.
    At first you have the standard straight-chain structure; then to gain isomers, rearrange the carbons to get branched chain alkanes. For pentane, you could for example have 2-methylbutane or 3-methylbutane, or 2-ethylpropane. Remembering the bond angles and that the bond can rotate, it wont be an isomer if you put a 'group' on the 'first' carbon, as rotating the bond will give the original structure in reality.

    So as long as you have the same molecular formula and a different structure no matter how you look at the molecule, you've got isomers
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    (Original post by Wintabix)
    http://www.thestudentroom.co.uk/atta...6&d=1357952433
    http://www.ocr.org.uk/Images/135164-...urces-june.pdf

    Hi can someone please explain how you get the answer for 4eii? It's the Hess's cycle one?
    I'm just thinking shouldn't it be a negative value because its reacting with oxygen?

    Thanks
    I was going to type it, but drawing is easier

    Posted from TSR Mobile
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    (Original post by chigyy)
    In nucleophilic substitution, do I have to show the intermediate?
    Would there be an intermediate??
    Say it's KOH + 1-Iodobutane
    I think first step shows nucleophile (in this case OH)"attacking" the slightly positive carbon and the C-I bond breaking.
    Second step shows the products Butanol and KI or I-
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    Hi guys was just marking jun 2010 paper and was confused if i would get a mark or not?
    Q 4iii) Give an equation to show the reaction between ethanol and acidified dichromate ions. Use [0] to represent the acidified dichromate ions, the oxidising agent (2 marks)

    mark scheme : CH3CH2OH + [O]  CH3CHO + H2O
    OR CH3CH2OH + 2[O]  CH3COOH + H2O
    Correct organic product 
    Balanced equation 

    i got C2H5OH + [OH] --> C2H4O + H2O ( i never know whether to use simplified formula or structural formula??)
    please help - i'll really appreciate it
 
 
 
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