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**Chemistry...Before/After

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    #512
    Mista
    Registered Users Posts: 183 ✭✭Mista


    TMCGY wrote: »
    Yea but it asked in moles per litre??

    I'm talking about the mass of Na2CO3 part.. for the titration I used 0.05 :)


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    #513
    ei.sderob
    Closed Accounts Posts: 108 ✭✭ei.sderob


    Dicksboro_man wrote: »
    have the paper in front of me here, "marble chips in excess", where does it say they're not?? :)

    LOl, typo by me sorry. I mean WERE.


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    #514
    K_1
    Closed Accounts Posts: 326 ✭✭K_1


    ei.sderob wrote: »
    Got -2275 or something for 6. Was pretty sure I was right. Isn't a 3 digit number very small when it comes to the heat of formation for such a long alkane?

    Think it was -224. Would be small for heat of combustion, not for heat of formation though.


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    #515
    leaveiton
    Closed Accounts Posts: 1,778 ✭✭✭leaveiton


    Agh, got the calculation in Q1 wrong. Made a really stupid mistake :(


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    #516
    Duffman K
    Registered Users Posts: 127 ✭✭Duffman K


    Paper didnt go too well for me at all, the last part of Q2 i didnt get,

    Anyone think that the 2nd half of Q5 was alot harder than usual ?
    Q1 fine
    Q2 tricky last part, didnt have a clue
    Q3 i think I got Mr of around 58 I think
    Q4 Ok
    Q5 Unusual 2nd part
    Q6 I think i got around -2,500kjmol :L
    Q7 was grand
    Q9 Never did that second part of the rate of reaction question before,
    Q11 (a) was ok,

    disappointed, Was really hoping for a B3, dont think I have it now:(


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    #517
    ei.sderob
    Closed Accounts Posts: 108 ✭✭ei.sderob


    K_1 wrote: »
    Think it was -224. Would be small for heat of combustion, not for heat of formation though.

    Ok so! Got a 40 mark window for the A1, fingers crossed.


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    #518
    TMCGY
    Registered Users Posts: 44 ✭TMCGY


    Mista wrote: »
    I'm talking about the mass of Na2CO3 part.. for the titration I used 0.05 :)

    What did you get for moles per litre?


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    #519
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    K_1 wrote: »
    Think it was -224. Would be small for heat of combustion, not for heat of formation though.

    Agreeing with this. I'm pretty certain I got that right, I was pretty careful with it.


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    #520
    Mista
    Registered Users Posts: 183 ✭✭Mista


    TMCGY wrote: »
    What did you get for moles per litre?

    0.12 I think? Thats off the top of my head though, can't be bothered gettin my sheet :P


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    #521
    kyle84
    Registered Users Posts: 21 ✭kyle84


    course u were


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    #522
    Hayezer
    Registered Users Posts: 652 ✭✭✭Hayezer


    I didn't even attempt heat of formation cus I was wondering wat the equation was :( what was the equation you wer meant to use?


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    #523
    TMCGY
    Registered Users Posts: 44 ✭TMCGY


    Mista wrote: »
    0.12 I think? Thats off the top of my head though, can't be bothered gettin my sheet :P

    Oh yay i got that too!! :)


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    #524
    Mista
    Registered Users Posts: 183 ✭✭Mista


    Hayezer wrote: »
    I didn't even attempt heat of formation cus I was wondering wat the equation was :( what was the equation you wer meant to use?

    8C + 9H2 --> C8H18


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    #525
    RedTexan
    Registered Users Posts: 217 ✭✭RedTexan


    I got plus 224?


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    #526
    RedTexan
    Registered Users Posts: 217 ✭✭RedTexan


    RedTexan wrote: »
    I got plus 224?
    Oh I see were I went wrong, will only be a couple of marks hopefully


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    #527
    Hayezer
    Registered Users Posts: 652 ✭✭✭Hayezer


    Mista wrote: »
    8C + 9H2 --> C8H18

    And then you just slotted in the values, product minus reactants? My god :( so dissapointed


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    #528
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    Liveforrugby wrote: »
    ... that's my point. In the question the forward reaction was actually

    I3 going to I + I2. Do you understand? You had to either reverse it or inverse your Kc.

    What I was saying was that it doesn't matter which arrow is on top. The reactants were on the left side, they were placed in the reaction vessel, that means the right side of the equation is the products. If the I3 were placed in the reaction vessel, it would be on the bottom of the Kc expression.


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    #529
    TMCGY
    Registered Users Posts: 44 ✭TMCGY


    Anyone know what answers are to part e of volitile liquid one??:cool:


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    #530
    Rossie17
    Registered Users Posts: 111 ✭✭Rossie17


    Could anyone with the paper handy there scan it please?


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    #531
    leaveiton
    Closed Accounts Posts: 1,778 ✭✭✭leaveiton


    Yeah I got -224 as well and my equations all cancelled out at the end so I'm fairly sure that's right


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    #532
    Helloxoxo
    Registered Users Posts: 49 ✭Helloxoxo


    RedTexan wrote: »
    RedTexan wrote: »
    I got plus 224?
    Oh I see were I went wrong, will only be a couple of marks hopefully

    I think I got -224 :/


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    #533
    Pepperr
    Registered Users Posts: 63 ✭✭Pepperr


    Hayezer wrote: »
    And then you just slotted in the values, product minus reactants? My god :( so dissapointed

    I'm not sure about them, but what I did was set up an equation, then balance it so I had C8H18 + 12.5O2 --> 9H2O + 8CO2

    Set up the hess equation so its 9h2o + 8co2 - C8H18 = -5502

    sub in and multiply in the values, swing it around and you should get -224


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    #534
    RedTexan
    Registered Users Posts: 217 ✭✭RedTexan


    TMCGY wrote: »
    Anyone know what answers are to part e of volitile liquid one??:cool:
    I said the boiling point of water would be below that of the non-volatile liquid and the other part was a mass spectrometer


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    #535
    TheHazer
    Registered Users Posts: 9 ✭TheHazer


    Anyone else notice that the heat of formation of 2,2,4 trimethylpentane was -224?

    Sneaky declan :p


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    #536
    dmca93
    Closed Accounts Posts: 104 ✭✭dmca93


    Cautiously optimistic about the paper, we'll know all in August I suppose. I really like Q.6, did any one else say but-1-ene for the possible compound?

    Also I see some people also got a number around 700~ for the kc? That's what I got so I'm a little more confident about that. And for the question about conc of I3 did you guys say it would be reduced because the startch would remove the I2 and thus the equilibrium would have to shift back to the left to replace the lost I2?


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    #537
    RedTexan
    Registered Users Posts: 217 ✭✭RedTexan


    dmca93 wrote: »
    Cautiously optimistic about the paper, we'll know all in August I suppose. I really like Q.6, did any one else say but-1-ene for the possible compound?

    Also I see some people also got a number around 700~ for the kc? That's what I got so I'm a little more confident about that. And for the question about conc of I3 did you guys say it would be reduced because the startch would remove the I2 and thus the equilibrium would have to shift back to the left to replace the lost I2?
    said but-2-ene, it's all good, and that's what I said about the starch part too


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    #538
    Dicksboro_man
    Registered Users Posts: 414 ✭✭Dicksboro_man


    hollingr wrote: »
    Maths questions answers I got:

    1. b) 2.65 g Na2CO3 used

    e) i) 2.5 moles/L , ii) 91.25 g/L

    got totally different ans for those. 0.12 m/L and 4.38 g/L

    i could be wrong though


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    #539
    Pepperr
    Registered Users Posts: 63 ✭✭Pepperr


    dmca93 wrote: »
    Cautiously optimistic about the paper, we'll know all in August I suppose. I really like Q.6, did any one else say but-1-ene for the possible compound?

    Also I see some people also got a number around 700~ for the kc? That's what I got so I'm a little more confident about that. And for the question about conc of I3 did you guys say it would be reduced because the startch would remove the I2 and thus the equilibrium would have to shift back to the left to replace the lost I2?

    Yes to the last part and to the but-1-ene.


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    #540
    Saracarroll
    Registered Users Posts: 64 ✭✭Saracarroll


    ei.sderob wrote: »
    I was soooo close to not seeing the fact that the marble chips weren't in excess!


    This doesn't matter as it is only the conc that was changed


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    #541
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    dmca93 wrote: »
    Cautiously optimistic about the paper, we'll know all in August I suppose. I really like Q.6, did any one else say but-1-ene for the possible compound?

    Also I see some people also got a number around 700~ for the kc? That's what I got so I'm a little more confident about that. And for the question about conc of I3 did you guys say it would be reduced because the startch would remove the I2 and thus the equilibrium would have to shift back to the left to replace the lost I2?

    I said methylpropene.

    and yeah that's what I said :)


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