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    (Original post by needtosucceed=))
    hello thought it was a fairly easy paper, few tricky things but generally okay. better than june 2012 not as easy as jan 2013. how did you find it? how you feeling about f325?
    I thought it was ok. I'm hoping it's not a too easy paper as I make silly mistakes and so low grade boundaries would be best. It's just fuel cells where i drop marks. I'm so gutted I got a B in January though, i made so many silly mistakes. How are you finding it?
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    (Original post by eggfriedrice)
    "a student wants to determine lattice enthalpy of Na2CO3. Suggest why it's difficult. "
    I said because it's hard to separate the ion into the individual elements which was wrong, but I don't understand the answer for it.
    The answer says "requires formation of ions from C and O" doesn't that mean it's hard to just react C and O?
    This is due to the Limitation not Physically but of the Model you are using.

    For the Born-Haber Cycle for Lattice Enthalpy of Formation at A-Level Chemistry you can't use Compounds + An Element. At Higher Levels you can extend the Born-Haber Cycle, or a similar model.

    But for our model - You can only use Element + Element.
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    (Original post by eggfriedrice)
    If I had two half equations set in a chemical series;

    Ni2+ + 2e- <=> Ni E cell =-0.25
    Fe3+ + e- <=> Fe 2+ E cell = 0.77

    If I made a cell, Ni electrode would be the negative electrode and so the equation would be Ni -> Ni2+ + e-thus it's being oxidised.
    Surely only the species at the positive electrode would be reduced.
    Yes, I think so too, okay ignore my last rule
    Just follow w/e instructions given in the question.
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    (Original post by JimmyA*)
    I thought it was ok. I'm hoping it's not a too easy paper as I make silly mistakes and so low grade boundaries would be best. It's just fuel cells where i drop marks. I'm so gutted I got a B in January though, i made so many silly mistakes. How are you finding it?
    thats true, but hopefully the paper isnt as bad as januarys. did you do f325 in january then?
    I'm finding it okay, dont feel as prepared for it as I did for f322 though, but hopefully if i've done well in that I wont need as high a mark on this paper
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    (Original post by Theafricanlegend)
    is there a relationship between pka and ph?
    The Henderson Hasselbalch equation
    pH=pka+log (A-/HA)

    You can simply derive this from using Maths and the Fundamental Equations, this is what I do, no need to learn this.


    Then for the Question which you did, the fact which you don't need to know is:
    At half the equiv/neautralisation point, pH=pKA

    What you do need to simply know is that for Practical reasons, we often may make choices based on this pH=pKa i.e. The Question with the Sour Tang Sweets.

    Hope that helps.
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    Alas I procrastinate! Time for me to Mark Jan 13 which wasn't actually as bad as I thought. Need to Keep Calm and Carry on! I'll ask my Teacher for a bit of help tomorrow but I think I should be alright.

    Time to do some real work - Chem 4.
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    (Original post by Better)
    This is due to the Limitation not Physically but of the Model you are using.

    For the Born-Haber Cycle for Lattice Enthalpy of Formation at A-Level Chemistry you can't use Compounds + An Element. At Higher Levels you can extend the Born-Haber Cycle, or a similar model.

    But for our model - You can only use Element + Element.
    Aha I see. But how come in the next question it asks you to make a born haber cycle using solution and hydration enthalpies and you're expected to put CO3 ^-2?
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    (Original post by Better)
    Alas I procrastinate! Time for me to Mark Jan 13 which wasn't actually as bad as I thought. Need to Keep Calm and Carry on! I'll ask my Teacher for a bit of help tomorrow but I think I should be alright.

    Time to do some real work - Chem 4.
    I've not even started chem 4 yet. Going to start after C3 on thursday
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    (Original post by eggfriedrice)
    Aha I see. But how come in the next question it asks you to make a born haber cycle using solution and hydration enthalpies and you're expected to put CO3 ^-2?
    From a Quick Google Search, University Chemistry websites confirm what I'm saying

    Born Haber Cycle = Element + Element (Usually Halogen and Metal) --> Compound.

    "Born-Haber Cycle. A series of hypothetical steps and their enthalpy changes needed to convert elements to an ionic compound


    Enthalpy of Hydration is a completely different Cycle, and hence it does not have the same Limitations.
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    (Original post by JimmyA*)
    I've not even started chem 4 yet. Going to start after C3 on thursday
    Well with a name like Jimmy A* you've given me confidence...

    Someone told me I have no choice I should get the Chem 4 done as well by Saturday.

    Just did C3 January 2013 today. Lol think I will enjoy the C3 Exam....... I've put in so much work though (30 Past Papers). My Maths before was a complete joke to now. A-Level Maths is just an Algebra test.
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    (Original post by Better)
    Well with a name like Jimmy A* you've given me confidence...

    Someone told me I have no choice I should get the Chem 4 done as well by Saturday.

    Just did C3 January 2013 today. Lol think I will enjoy the C3 Exam....... I've put in so much work though (30 Past Papers). My Maths before was a complete joke to now. A-Level Maths is just an Algebra test.
    Haha, i don't actually get A*'s although I'm aiming for an A* in maths. C4 is the problem at the moment though as i keep on getting around 80-85.
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    (Original post by Better)
    From a Quick Google Search, University Chemistry websites confirm what I'm saying

    Born Haber Cycle = Element + Element (Usually Halogen and Metal) --> Compound.



    Enthalpy of Hydration is a completely different Cycle, and hence it does not have the same Limitations.
    Hmm ok then. So born haber for lattice enthalpy is entirely elements. And born haber for solution /hydration is just any compound? :s then again lattice enthalpy is in the haber cycle for hydration haha oh well.

    Btw it seems like we're doing the same subjects; maths, chem and physics.
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    (Original post by eggfriedrice)
    Hmm ok then. So born haber for lattice enthalpy is entirely elements. And born haber for solution /hydration is just any compound? :s then again lattice enthalpy is in the haber cycle for hydration haha oh well.

    Btw it seems like we're doing the same subjects; maths, chem and physics.
    Yeah haha come at me bro.

    Time for me to Drink my Protein Shake and get back to work. Catch you all in a bit good luck!
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    Can anybody help me? I struggle with the how to set up [said] experiment. Does anybody have a list of experiements that we should know how to set up.

    Thanks
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    Could someone please help explain how you would find the other half equation at the other electrode?

    At one electrode : O2 + 4H+ +4e- ---> 2H2O

    Overall equation : CH3OH + 1.5O2 ---> CO2 + 2H2O

    Thank you.
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    Why when tin (II) chloride is added to Fe3+ and reduces it to Fe2+, I said the equation would be

    Sn 2+ + Fe3+ -> Sn3+ - Fe 2+
    But it should actually be Sn2+ + 2 Fe3+ -> Sn4+ + 2Fe2+

    Why is my one wrong?

    Question 8 b Jan 2013.
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    (Original post by shootingstars123)
    Could someone please help explain how you would find the other half equation at the other electrode?

    At one electrode : O2 + 4H+ +4e- ---> 2H2O

    Overall equation : CH3OH + 1.5O2 ---> CO2 + 2H2O

    Thank you.
    You should remember that the two equations should add up to give you the overall equation and that the number of electrons gained must be equal to the number of electrons lost.

    the other half equation must have methane and must make CO2, it should also eliminate the 4H+ as they are not in the overall equation.


    CH3OH --> 4e^- + 4H^+ + CO2
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    (Original post by zakkaz)
    You should remember that the two equations should add up to give you the overall equation and that the number of electrons gained must be equal to the number of electrons lost.

    the other half equation must have methane and must make CO2, it should also eliminate the 4H+ as they are not in the overall equation.


    CH3OH --> 4e^- + 4H^+ + CO2
    That makes sense, but the mark scheme says:

    CH3OH +H2O ---> 6H+ +6e– +CO2

    I'm not sure how they got this
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    What is the hardest f325 past paper you have done guys? I wanna have a go!!


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    (Original post by Better)
    The Henderson Hasselbalch equation
    pH=pka+log (A-/HA)

    You can simply derive this from using Maths and the Fundamental Equations, this is what I do, no need to learn this.


    Then for the Question which you did, the fact which you don't need to know is:
    At half the equiv/neautralisation point, pH=pKA

    What you do need to simply know is that for Practical reasons, we often may make choices based on this pH=pKa i.e. The Question with the Sour Tang Sweets.

    Hope that helps.
    what about 7dii ? could you tell me how that works?
 
 
 
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