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Edexcel A2 Chemistry Exams -6CH04 (14th June) and 6CH05 (22nd June) Discussion Thread Watch

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    Please can someone explain the second marking point on the markscheme for this question? I don't get what it means by [H+] is greater than expected. I get how the equilibrium shifts to the right, but not this "greater than expected thing". Can someone please explain this? Thanks



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    sup guys. Has anyone ever seen a mark scheme where they don't accept displayed formula when the question asks for structural?
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    Goiys what's the formula for % uncertainty again?
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    (Original post by Don Pedro K.)
    Goiys what's the formula for % uncertainty again?
    error/value*100

    e.g if a temperature is measure at 25 degrees and the error is +-0.5 degrees, 0.5/25*100
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    (Original post by Funky_Giraffe)
    Please can someone explain the second marking point on the markscheme for this question? I don't get what it means by [H+] is greater than expected. I get how the equilibrium shifts to the right, but not this "greater than expected thing". Can someone please explain this? Thanks



    I think what they're saying is that with ethanoic acid, you get the usual dilution by a factor of 10 and thus increase by 1.0 but because of the equilibrium that ethanoic acid forms with water, dilution shifts the equilibrium to the right so more H+ ions are produced, meaning that the pH doesn't increase as much?
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    (Original post by Don Pedro K.)
    I think what they're saying is that with ethanoic acid, you get the usual dilution by a factor of 10 and thus increase by 1.0 but because of the equilibrium that ethanoic acid forms with water, dilution shifts the equilibrium to the right so more H+ ions are produced, meaning that the pH doesn't increase as much?
    Oh I see So it's kind of comparing the full dissociation of HCl with the partial dissociation of CH3COOH?
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    What are the factors that affect titre values?

    Like what happens if a larger mass is used?
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    (Original post by Funky_Giraffe)
    Oh I see So it's kind of comparing the full dissociation of HCl with the partial dissociation of CH3COOH?
    That's what it seems like, because if you think about it, HCl(g) + H2O(l) --> H3O+Cl-(aq) is not an equilibrium, so dilution doesn't "shift" anything I think? But with ethanoic acid it does form an equilibrium so Le Chatalier's principles apply. I may be wrong though but this is my reasoning xD
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    What's the error in a burette? +-0.05cm3?
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    Guys how was the paper? I found it pretty solid, the MCQ's were amazing
    Although I'm worried about the last 5 marks
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    i have a few questions

    - what if the product in an equilibrium is only a solid, and they ask you to determine the expression for kp, would you divide the reactants by 1?

    - When using the lattice enthalpies from the data booklet do you use the theoretical or experimental value ?

    - does hydrogenation only break C=C bonds or can it also break C=O into C-OH seeing as hydrogenation is the addition of hydrogen to break double bonds!?

    - and with the definition for Dynamic equilibria would you describe it as ' The rate of the forward and backward reaction are equal , and the concentration of products and reactants are the SAME OR EQUAL' ?
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    Is the IAL thread? If not, ignore my post above
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    (Original post by azefayuu)
    Guys how was the paper? I found it pretty solid, the MCQ's were amazing
    Although I'm worried about the last 5 marks
    the paper is to be taken at 1:30 ?
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    (Original post by azefayuu)
    Is the IAL thread? If not, ignore my post above
    could you tell us what were the main topics that came up ?
    because there usually very similar
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    (Original post by tayloryeah)
    could you tell us what were the main topics that came up ?
    because there usually very similar
    Haha no.
    Different timezones.
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    (Original post by tayloryeah)
    could you tell us what were the main topics that came up ?
    because there usually very similar
    he is lying ignore him,
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    (Original post by Don Pedro K.)
    I'm afraid you forgot to do something natcupine!!

    ihaspotato You would have to double the 38.5 sine the H2 is in a 2:1 molar ratio to the CH3OH So it's 77.5 - 77 = 0.5 moles
    Oh yeah!! 2 hours before the exam lol :rolleyes: Thanks for correcting me!
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    how do you work out order of reaction when other concentrations are changing?

    E.G. question 14 cii
    http://qualifications.pearson.com/co...e_20150610.pdf
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    how do you work out order of reaction when other concentrations are changing eg q 14 cii
    http://qualifications.pearson.com/co...e_20150610.pdf
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    (Original post by natcupine)
    Oh yeah!! 2 hours before the exam lol :rolleyes: Thanks for correcting me!
    No problem
 
 
 
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