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

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    (Original post by TeaAndTextbooks)
    Can anyone help with this question please? I'm kind of confused.


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    Firstly, work out the number of moles of NaOH used in the titration using moles = volume * concentration / 1000.

    Then, work out the number of moles of HCl present at equilibrium - since the HCl was used as a catalyst, this will be the same as the original number of moles (which you can work out using the info provided).

    Then, work out number of moles of ethanoic acid left at equilibrium by taking away the number of moles of HCl from the number of moles of NaOH, since the NaOH reacted with both the ethanoic and hydrochloric acids.

    From here, you can work out the other equilibrium moles etc.
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    (Original post by Funky_Giraffe)
    Hey guys, can someone please explain what the heck this question is on about? How are we supposed to know to compare experimental and theoretical lattice energies?!

    You compare them to show that one difference is greater than the other - supports the fact that one has more covalent character than the other surely?
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    http://qualifications.pearson.com/co...-June-2014.pdf

    Help with Q9 d ii

    Answer is negative is mark scheme, even though I get a +ve answer on my calculator, is this because in the question above it states temperatures Rises which means its an exothermic reaction hence the negative sign or am I just doing the wrong thing?.
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    any hep with this one
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    (Original post by Don Pedro K.)
    You compare them to show that one difference is greater than the other - supports the fact that one has more covalent character than the other surely?
    Oh right. So if there's more covalent character, there's a greater difference between the values and this means it will dissolve easier in solution? Or is it the other way around? Forgotten all my AS!!
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    (Original post by Supermanxxxxxx)
    Name:  Screen Shot 2016-06-13 at 18.28.37.png
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    any hep with this one
    Firstly, find the number of moles of HCl and NaOH. Take their difference to get the moles of ethanoic acid remaining in equilibrium. The moles you will get are the moles that are remaining after reaction so initial moles-moles that have reacted= moles at equilibrium. Using this relationship, you can deduce the moles of the ester and water as well as the alcohol. Substitute your answer in the Kc expression.

    Note: To calculate moles of NaOH, use the mean titre.
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    Hey guys good luck for tomorrow!!!
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    Why is the answer to MCQ 2=B and not A?
    Also why is the answer to 5a = B and not A?
    https://c838cff4741acb48ae1ed62e5992...0Chemistry.pdf

    Thanks in advance
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    (Original post by Funky_Giraffe)
    Look back to post #641 on this page http://www.thestudentroom.co.uk/show...1#post65718631

    I did an explanation
    Thanks

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    (Original post by Don Pedro K.)
    F



    Firstly, work out the number of moles of NaOH used in the titration using moles = volume * concentration / 1000.

    Then, work out the number of moles of HCl present at equilibrium - since the HCl was used as a catalyst, this will be the same as the original number of moles (which you can work out using the info provided).

    Then, work out number of moles of ethanoic acid left at equilibrium by taking away the number of moles of HCl from the number of moles of NaOH, since the NaOH reacted with both the ethanoic and hydrochloric acids.

    From here, you can work out the other equilibrium moles etc.
    Thank youu

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    (Original post by Funky_Giraffe)
    Hey guys, can someone please explain what the heck this question is on about? How are we supposed to know to compare experimental and theoretical lattice energies?!

    The lattice enthalpy values are given in the data booklet, so you compare them. LiCl will not have a large between its experimental value and theoretical value, while LiI will have a large difference, because the Li, can polarise the larger iodide more that it can polarise the Chloride ion, so lithium iodide shows more covalent character, hence it is more soluble in organic solvents
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    (Original post by dj3k)
    Why is the answer to MCQ 2=B and not A?
    Also why is the answer to 5a = B and not A?
    https://c838cff4741acb48ae1ed62e5992...0Chemistry.pdf

    Thanks in advance
    Question 2: When talking about thermodynamic feasibility, this is ALWAYS talking about entropy. You chose to talk about activation energy, which is to do with kinetics.

    So something that is kinetically stable will have a high activation energy.

    Something thermodynamically stable will have a more negative ΔS(total).

    Question 5: count the moles of gas on each side of the equilibrium equation, and you should be able to figure that one out. Why it isn't A is because it is B.

    Lol jk but if a gas is more pressured then surely it helps it go through the reactor anyway? Much like pushing harder to get onto a packed train will make people want to move out of the way so they aren't so squashed.
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    (Original post by Funky_Giraffe)
    Oh right. So if there's more covalent character, there's a greater difference between the values and this means it will dissolve easier in solution? Or is it the other way around? Forgotten all my AS!!
    Greater difference = greater deviation from perfect ionic model = more covalent character = more easy to dissolve in organic solvent
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    Hey! COuld someone tell me when to and when not to include H2O in the equilibrium constant expression? Because in the CHem U6 exam, we were supposed to include water in the expression, I thought the Ionization of water is a constant. Isn't that so?
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    Help, I have no idea how you do this.

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    (Original post by TeaAndTextbooks)
    Help, I have no idea how you do this.

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    Which paper is this from?
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    (Original post by Sandy_Vega30)
    Hey! COuld someone tell me when to and when not to include H2O in the equilibrium constant expression? Because in the CHem U6 exam, we were supposed to include water in the expression, I thought the Ionization of water is a constant. Isn't that so?
    include water if all the reactants are liquids
    don't include water if water is the solvent (i.e. if the reactants are (aq))
    hope I helped
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    (Original post by Don Pedro K.)
    Which paper is this from?
    Jan 15 IAL

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    (Original post by Sandy_Vega30)
    Hey! COuld someone tell me when to and when not to include H2O in the equilibrium constant expression? Because in the CHem U6 exam, we were supposed to include water in the expression, I thought the Ionization of water is a constant. Isn't that so?
    Include h20 in the expression when its a product but not when its a reactant, thats how i learnt it in class
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    (Original post by TeaAndTextbooks)
    Help, I have no idea how you do this.

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    OMG I did this question like 5 minutes ago! Let me just take a photo of what I wrote
 
 
 
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