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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD watch

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    (Original post by postexamtalk)
    I got the same except i left out the observations, did it explicitly ask you to mention what you observe in the question?
    It was to do with the Iodide ions, either brown to colourless or colourless to brown.
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    (Original post by MrZebraCookie)
    lol yeah, i wrote like 6 equations for that one :/
    I also reacted the Cr2O7 with the Cr3+ woops
    I don't think you could.. CR3+ needs to act as a reducing agent meaning it needs to be on the RHS on the equation, the key was to use the crO7/cr3+ equation and reverse it, meaning the only thing it could have reacted with was feO4
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    (Original post by HFancy1997)
    Thats correct method but x=4

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    I must have typed the wrong numbers into my calculator at some point but hopefully I got 3 or 4/5 marks.
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    what the f is a standard form??????????
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    (Original post by Brandoncarlin)
    What I got for the 4-step mechanism:

    Overall equation: H2O2 + 2I- + 2H+ forms I2 + 2H2O

    H2O2 + I- forms IO- + H2O
    IO- + H+ forms HIO
    HIO + I- forms I2 + OH- (given in question)
    OH- + H+ forms H2O
    H2O2 + I- forms HIO + OH-
    H+ + OH- forms H2O
    HIO + I- forms I2 + OH- (given)
    H+ + OH- forms H2O

    Both valid?
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    (Original post by Brandoncarlin)
    What I got for the 4-step mechanism:

    Overall equation: H2O2 + 2I- + 2H+ forms I2 + 2H2O

    H2O2 + I- forms IO- + H2O
    IO- + H+ forms HIO
    HIO + I- forms I2 + OH- (given in question)
    OH- + H+ forms H2O
    yeah boi! Hope we're right as this does match the overall...
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    guys vote now on how you think the paper was.

    http://www.thestudentroom.co.uk/show....php?t=4180760
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    For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?
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    (Original post by postexamtalk)
    I got the same except i left out the observations, did it explicitly ask you to mention what you observe in the question?
    It did yeah, but I wouldn't worry to much as the equilibrium shifts will get you most the marks
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    (Original post by tomlam)
    It was to do with the Iodide ions, either brown to colourless or colourless to brown.
    Isn't it to do with the black-grey precipitate (I2) and the yellow precipitate (AgI)?
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    (Original post by maisym00)
    For the equilibrium question I put: I- reacts with Ag to form agI (yellow ppt), therefore the position of equilibrium will shift to the left to restore I- conc. As a result, more aqueous iodine was formed so the position of equilibrium of 1 will also shift to the left, therefore more grey/black solid iodine is formed. For the electrochemistry question I needed up with two equations. The oxidising agent one where Cr+3 reacts with AL and the reducing agent one where Cr+3 reacts with feO4- or something. Anyone else?
    for the cr+3 to cr2o7 part - I thought that as they only gave you cr3+ the reaction had to backwards - so you could pretty much switch the sign on the ev - and that gave me two equations - I don't exactly remember what. I'm really quite unsure whether that was a correct assumption.
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    (Original post by cr7alwayz)
    For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?
    G was negative so the reaction was feasible.
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    For the very first question did people get Cu(H20)2(NH3)4 or Cu(nh3)4. I put the first one with deep blue as the colour becuase I didnt know what the colour of Cu(NH3)4 was.
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    Does anyone have a copy of the paper?
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    (Original post by cr7alwayz)
    For using a calculation to explain why K2SO4 can dissolve at 25oC was the entropy change 0.02 or something which is positive so the reaction is feasible?
    Temp was 298K you get negative 43 or something so its feasible as delta g is neg

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    How many marks was the AgNO3 equilibrium shift?
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    (Original post by lai812matthew)
    what the f is a standard form??????????
    (something between 1 to 10) times 10^(something)

    Can't remember the exact answer, but 0.029 in standard form would be 2.9 x 10^(-2)
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    (Original post by maisym00)
    For the equilibrium question I put: I- reacts with Ag to form agI (yellow ppt), therefore the position of equilibrium will shift to the left to restore I- conc. As a result, more aqueous iodine was formed so the position of equilibrium of 1 will also shift to the left, therefore more grey/black solid iodine is formed. For the electrochemistry question I needed up with two equations. The oxidising agent one where Cr+3 reacts with AL and the reducing agent one where Cr+3 reacts with feO4- or something. Anyone else?
    Exactly what I did!

    (Original post by EricPiphany)
    Don't worry you'll be fine.

    Speaking to people who sat the exam with me, lots of them messed up the buffer question.

    I certainly messed up parts. But with high UMS last year, and good UMS in the first exam, I should have the A I need.
    Yeah, hopefully A* boundary is low and I'm safely into it. I'm really counting on chem to be one of the 2A* in need to make my offer
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    What did people get for the empirical formula one?

    I got the fact it was the same as the molecular formula but not 100% on it.
 
 
 
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