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    (Original post by monkeyDace)
    Yo ppl what is the chances of me revising module 3 this evening and get and an A on the exam (I havent revised this one since january) ?
    It will be a doddle. You can master module 3 in like an hour.
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    In an electrochemical cell what is the point in the salt bridge?
    I understand it has ions that do not react with either half cells like K+ and NO3- but what is its purpose?
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    (Original post by CoventryCity)
    In an electrochemical cell what is the point in the salt bridge?
    I understand it has ions that do not react with either half cells like K+ and NO3- but what is its purpose?
    to complete the circuit
    allows ions to be transferred between the two half cells
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    Can someone please help explain the role of carbonic acid- hydrogencarbonate as a buffer in the control of blood pH pleasee?
    H2CO3 --> HCO3- + H+
    H2O + CO2 --> H+ + HCO3-

    I don't understand when the pH increases/decreases etc.
    ?
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    anyone have a list of questions and answers?
    I have completed all the past papers
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    judging by yesterday's disastrous biology paper, a trip to the zoo would probably be more useful for revision than the textbook :colonhash:
    hate OCR
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    Yep, I'm in exactly the same situation. Screwed up yesterday and now really need to get a B tomorrow. Good luck to you - think I'm going to need it!!!
    Honestly, I don't think it's going to happen for me. I was so focussed on f215 that i've done hardly any revision for this.
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    (Original post by .r.)
    judging by yesterday's disastrous biology paper, a trip to the zoo would probably be more useful for revision than the textbook :colonhash:
    hate OCR
    amen! Countryfile would have helped me more than all 3 text books I used...
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    (Original post by yesioo)
    Honestly, I don't think it's going to happen for me. I was so focussed on f215 that i've done hardly any revision for this.
    OGHHH, YES, SAME!!! And now i am freaking out over this. I don't think i will ever get over yesterday. Never.
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    when an ionic combound dissolves in water its entalpy change of solution is +ve and lattic entalpy is -ve
    so entalpy of hydration= lattic entalpy + entalpy of solution
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    Has anyone got a link to any past papers excluding June 2010/Jan 2011.
    Old spec ones would be nice as well, need all the questions I can get!
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    is it in the morning or afternoon ?
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    (Original post by 2141)
    is it in the morning or afternoon ?
    afternoon, 2 o clock thank god.
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    (Original post by TsunKit)
    Has anyone got a link to any past papers excluding June 2010/Jan 2011.
    Old spec ones would be nice as well, need all the questions I can get!

    I put up Jan'11 on the last page

    Negged for a mistake? :') This place just gets better
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    (Original post by hellosarah)
    [H+] = Ka x [acid]/[salt] right?
    Personally I only memorise the Ka equation and then rearrange it to get whichever part I need, much easier, trust me.
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    (Original post by Wilzyy)
    Personally I only memorise the Ka equation and then rearrange it to get whichever part I need, much easier, trust me.
    I keep askings things on here, then find the answer seconds later.. :/
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    (Original post by Maccees)
    I put up Jan'11 on the last page
    Thanks but I said excluding June 2010/Jan 2011.
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    (Original post by hellosarah)
    Can someone please help explain the role of carbonic acid- hydrogencarbonate as a buffer in the control of blood pH pleasee?
    H2CO3 --> HCO3- + H+
    H2O + CO2 --> H+ + HCO3-

    I don't understand when the pH increases/decreases etc.
    ?
    dunno what the second equation's all about but all you need to know is that the buffer is H2CO3 <---> H+ + HCO3-

    There's lots of weak acid because it hardly dissociates and lots of its conjugate base but not much H+

    When you add acid...the concentration of H+ increases, the added H+ reacts with the conjugate base producing more weak acid thereby shifting equilibrium to the left and minimising pH change (not increasing or decreasing it...but *minimising* the change)

    When you add alkiali, the concentration of OH- increase, the added OH- reacts with the H+ in the buffer producing H2O...the weak acids has to dissociate more to replace the reacted H+ ions, it does this by shifting equilibrium to the right hence minimising the pH change
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    (Original post by hellosarah)
    [H+] = Ka x [acid]/[salt] right?
    Ka = ([H+] [A-]) / [HA]
    So [H+] = Ka x ([HA] / [A-])
    So yes that is correct

    We assume [A-] = [Salt] as we get complete dissociation
    Is this calculating pH of buffers?
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    anyone have a list of practise questions and answers?
    I have completed all the past papers
 
 
 
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