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    (Original post by igobyursula)
    Hiya...

    Sorry if someone else has already answered this question for you.

    With 2+ hexa-aqua ions, basically (well my chemistry teacher told me because there is no distinction in the book(s))

    Its 3en which forms [M(en)3]2+ + 6H2O

    With 3+ hexa aqua ions it does something different.

    en is H2NCH2CH2NH2

    This is the following equation

    2[M(H2O)6 ]3+ + 3H2NCH2CH2NH2 ----> 2[M(H2O)3(OH)3] + 3H3NCH2CH2NH3

    This is because 3+ ions are slightly more acidic and can donate H+ more easily. Think of the reactions between the hexa aqua ions and carbonate ions.

    Hope this helps. I was completely muddled by it all initially. There is not actually any distinction in the book (I use Nelson Thornes) at all, but I think you are supposed to apply knowledge of the differences between the reactions betweeen carbonate with 2+ hexa aqua ions and 3+ hexa aqua ions. en is a bidentate ligand, as is the carbonate ion.
    Sorry to butt in. i didn't know that about 3+ ions with 'en'. But it kinda explains the question about Al3+ reacting with diaminoethane in January 2012 paper. The questtion says diaminoethane behaves like ammonia, So i thought you were meant to think, well Al3+ doesn't undergo substitution with ammonia, so its not going to undergo substitution with this ligand...didn't know there was a rule, thank you for sharing.
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    (Original post by JSN)
    thanks alot, cant rep you
    That's fine, just glad I could help
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    (Original post by lifeisgood2012)
    Does the value of emf increase if more electrons are released?
    (Original post by JSN)
    it gets more -ve i think but someone confirm this
    Emf should always be positive otherwise the spontaneous reaction doesn't occur. I think the emf decreases if more electrons are produced because that would lead to an increase in current in the circuit and as current increases, emf decreases but I'm not entirely sure

    Edit: thinking about it though that's more to do with physics and I think it would be unfair to assume everyone would know it so I'm not even sure if that would be tested in the exam. Did it come from a specific question in a past paper?

    Edit 2: never mind, I was thinking of resistance instead of current for some reason :rolleyes:
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    (Original post by crc290)
    Emf should always be positive otherwise the spontaneous reaction doesn't occur. I think the emf decreases if more electrons are produced because that would lead to an increase in current in the circuit and as current increases, emf decreases but I'm not entirely sure

    Edit: thinking about it though that's more to do with physics and I think it would be unfair to assume everyone would know it so I'm not even sure if that would be tested in the exam. Did it come from a specific question in a past paper?
    Nope i was just wondering.... on some papers... they give you like a table and one of the questions was explain why water reacts with flurorine... and you had to use the ecell values to explain it
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    (Original post by itssochaotic)
    Sorry to butt in. i didn't know that about 3+ ions with 'en'. But it kinda explains the question about Al3+ reacting with diaminoethane in January 2012 paper. The questtion says diaminoethane behaves like ammonia, So i thought you were meant to think, well Al3+ doesn't undergo substitution with ammonia, so its not going to undergo substitution with this ligand...didn't know there was a rule, thank you for sharing.
    Yes, exactly. Al, Fe (Cr is an exception when NH3 is in excess) do not undergo ligand sub with ammonia as they are more acidic and donate protons. Fe 2+ is less acidic and does not undergo ligand sub either, so its not really a hard and fast rule, but when they do ask about other species and the way they behave with hexa aqua ions , you just need to apply knowledge about the reactions we have been taught. My teacher saysthat it is not because they want to trick us. :rolleyes:
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    (Original post by lifeisgood2012)
    Nope i was just wondering.... on some papers... they give you like a table and one of the questions was explain why water reacts with flurorine... and you had to use the ecell values to explain it
    Ah right. Well ignore my explanation then because I think it was wrong anyway on those questions you usually just have to say that the potential for one electrode is higher than the other and that gets the marks
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    For http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF
    Qs 1a and 1bii, how do you know what the equations are? I don't understand what they mean when it says what's the eqn equal to the standard enthalpy of.....

    Thanks in advance
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    For question 4b

    http://papers.xtremepapers.com/AQA/C...W-QP-JAN04.pdf


    If the hydrogen ion concentration is reduced, equilibrium shifts to the left so more e- ions are accepted so EMF should increase? Why does it decrease?

    Thanks
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    Pls could someone explain what you would put for the reasoning..
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    (Original post by lifeisgood2012)
    Does the value of emf increase if more electrons are released?
    Absolutely not, EMF is independent of that.
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    Wow, are AQA serious. June 2012, the gradient of the line question is ridiculous. I only noticed the it didn't go exactly through the middle of the box after I'd seen the answer and zoomed in A LOT. No chance of me seeing that, not clear AT ALL. I'd never assume that it didn't pass directly through.
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    (Original post by popnit)
    Pls could someone explain what you would put for the reasoning..
    The answer is just " by definition "


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    (Original post by Extricated)
    For question 4b

    http://papers.xtremepapers.com/AQA/C...W-QP-JAN04.pdf


    If the hydrogen ion concentration is reduced, equilibrium shifts to the left so more e- ions are accepted so EMF should increase? Why does it decrease?

    Thanks
    When it moves to the side with the electrons, the emf always decreases for that paricular electrode


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    (Original post by Chris-69)
    Wow, are AQA serious. June 2012, the gradient of the line question is ridiculous. I only noticed the it didn't go exactly through the middle of the box after I'd seen the answer and zoomed in A LOT. No chance of me seeing that, not clear AT ALL. I'd never assume that it didn't pass directly through.
    It is actually ridiculous. I kept getting 0.1 but the markscheme says that it must not be that number unless the students has written 0.997.. Whatever it was. So ridiculous. I actually would not mind such a question but they need to make their graphs more clearm
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    (Original post by popnit)
    Pls could someone explain what you would put for the reasoning..
    Wouldn't it just be 0 and then for a reason just "by definition. The Standard Hydrogen Electrode is a reference point".
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    (Original post by igobyursula)
    Wouldn't it just be 0 and then for a reason just "by definition. The Standard Hydrogen Electrode is a reference point".
    Ahhh wasn't sure what to put for the by definition bit. Thank you
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    (Original post by poopnoddy)
    The answer is just " by definition "


    Posted from TSR Mobile
    Okay thank you
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    Guys can some tell me me if this is right:

    The question is: Defineenthalpy of atomisation

    I wrote:the enthalpy change when 1 mole of a gaseous atom is formed from an element inits standard state under standard conditions.

    Mark scheme says:
    Enthalpy changefor the formation of 1 mol of gaseous atoms (1)
    From the element (inits standard state) (1)

    What’s the difference between mol and mole?

    Also, say with calculation questions like calculating the latticeenthalpy of dissociation, if you get the right answer do you all marks?

    For the Jan 11 paper question 1.b) I got +771KJ mol-1

    Which is correct but the mark scheme says this: so do I get all three even though I have written this below?
    1(b) ∆HL = –∆Hf + ∆Ha + I.E. + 1/2E(Cl-Cl) + EA (1)
    = +411 + 109 + 494 + 121 – 364 (1)
    = +771 (kJ mol-1) (1)
    Or correct Born-Haber cycle drawn out
    –771 scores 2/3
    +892 scores 1/3
    –51 scores 1/3
    –892 scores zero
    +51 scores zero ignore units thanks in advance guys
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    (Original post by ryanj18)
    What’s the difference between mol and mole?
    No difference, mol is the symbol for mole, like kg is the symbol for kilogram
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    (Original post by igobyursula)
    It is actually ridiculous. I kept getting 0.1 but the markscheme says that it must not be that number unless the students has written 0.997.. Whatever it was. So ridiculous. I actually would not mind such a question but they need to make their graphs more clearm
    Yeah, if the graph was clear it was pretty straight forward; I also got 0.1. Wasn't at all clear.
 
 
 
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