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EDEXCEL CHEMISTRY 6B - 19th June - 12hrs passed!

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    so how was it for you guys?

    i had ********ng no idea of the first question (energetics). i'll probably get 2/10 on that question.

    did anyone do the 2nd question? there was a question asking you which of the reactions "alcohol+carboxylic acid" or "alcohol+acid chloride" gave a greater yield. i wrote alcohol+acid chloride because the ester could acid hydrolise in HCl back to the c.acid and alcohol. is that correct?

    the paper was OK overall, except the first question, which took me completely by surprise as it did not come up in any past paper.
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    I sort of rambled my way through question 1.

    Didn't know the definition of Hess's Law. Didn't know where the 30cm of HCL was meant to come in... I got 43KJ mole for first part and flopped on the 2nd part.

    Alternative questions: 3 - THANK YOU!!!!
    Question 4.... Slightly more dubious and complicated but at least there's no real calculations.

    Did half of question 2... then realised I couldn't do the maths properly and I only had a vague idea of the grignard (That was annoying because the mechanisms are easy)
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    q1) -43 kj/mol and +101.6 kj /mol
    2) ch3ch2mgbr is the grignard
    thats all i can remember for now.
    EDIT: oh and the mass of sodium propanoate was 1.8g
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    Awww... -.-
    I got a positive value

    Figures. It threw me off with Ethene. I used Ethane at first, then realised what it said.
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    It's a thermal decomposition.. the value must be positive

    My answer was around +50kJmol-1

    I dont usually say this but I thought that paper was really easy
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    if the temperature increases then its exothermic as energy is given to the surroundings so enthalpy should be negative.
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    (Original post by dreamer*girl)
    did anyone do the 2nd question? there was a question asking you which of the reactions "alcohol+carboxylic acid" or "alcohol+acid chloride" gave a greater yield. i wrote alcohol+acid chloride because the ester could acid hydrolise in HCl back to the c.acid and alcohol. is that correct?
    I put the acid chloride reaction gave the greater yield as an equilibrium is set up in the carboxylic acid reaction.
    I did questions 2 and 4... didn't have a clue about the hydrated copper ions or whatever they were... and wouldn't have been able to do the question about why water wouldn't react with the CCl4 (I remember my teacher telling us not to write about stearic hindrance, but I forgot what we were supposed to write)... meh.
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    The temperature only increases because you have to put energy into the system for the reaction to occur, therefore it's endothermic.
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    (Original post by Timba)
    It's a thermal decomposition.. the value must be positive

    My answer was around +50kJmol-1

    I dont usually say this but I thought that paper was really easy
    It certainly was rather easy. (Assuming revision was done)
    Which questions did you attempt?
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    The CCl4 question is from unit 5.

    Water has lone pair.
    Si contains d-orbitals C doesn't.
    Water can't attack the carbon but the silicon.

    I put it in waffly terms like that... so I expect that there's a chance I might lose marks from wording.
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    2 and 3, really nice questions!

    What I did get wrong was the TYPE of reagent that a grignard reagent is. I said electrophile but it's actually a nucleophile
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    meh easy paper.. just revised what didn't come up properly on unit 4 and 5, and voila. Apart from that.. I didn't revise anything from last year but cmon.. question 1 was adding and multiplying :rolleyes:.
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    i got -43 and +101.6 for the first question aswell
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    For question 4 - Last section. It talked about the pH when BaCrO4 was created and PbCrO4

    What was the answer to these?

    I put acidic in the first one... but i wasn't sure whether it's actually neutral buffer, where as the 2nd one is purely acidic.
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    this thread is pretty quiet...
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    I did q2 and 3,

    Question 1 I think I might have gotten the second part right but I didn't have the answer to the first part so I just put in the formulas and used a substituted value that I guess. The explanation part was okay, but again because it was all consequential on my first answer, only the theory was correct and the application of this made-up number that I used. Hopefully get me a few marks for doing that.

    Question 2 was ok-ish, but I forgot what ethanol and an ester make (only 1 mark)

    But I do remember that the other one gave the greater yield.

    Question 3 was my saviour, nice, easy, lots of theory and very little calculations. Maths is my worst subject ever. But there was a calculation I think for Ka that I did I can't remember what question that was, possible 2... That was a bit tricky but got there in the end. Can't remember my exact values but I do remember I first had to work out [H+] then I did something else to get conc and thus n, then finally I used the n = m x FM to get the 1.6 or 1.8 or something.

    That's all I remember but it wasn't a bad paper at all, I just wasn't prepared for enthalpy of neut and my ester/grignards chemistry is a bit rusty. Nevermind. At least the practical was spot on =[
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    (Original post by aminalia89)
    this thread is pretty quiet...
    It'll be filled tomorrow morning
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    how did u find <delta>H1 ? didn't u use the formula <delta>H = mc<theta> ?
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    (Original post by redmeg)
    i got -43 and +101.6 for the first question aswell
    yup thats what I got the second part was
    \Delta H=2\Delta H_2 - \Delta H_1
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    (Original post by BadExaminee)
    how did u find <delta>H1 ? didn't u use the formula <delta>H = mc<theta> ?
    yup exactly, use \Delta E=mc\Delta T

    then divide through by the number of moles (which was given) to find \latex \Delta H_1

    then convert from joules to kJ and remember that it would be negative as the temperature change is positive

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