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***2015 LC Chemistry - Higher Level - June 16th***

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24

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    #32
    blue_velvet
    Registered Users Posts: 16 ✭blue_velvet


    What was the percentage yield for benzoic acid?I think I got around 43%


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    #33
    Doctorhopeful
    Registered Users Posts: 200 ✭✭Doctorhopeful


    The_N4sir wrote: »
    I took A as 30-x so I guess i'll have to see what others got

    Ah **** i did X for both idk which is right... probably why it didn't work out so cleanly....


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    #34
    OMGeary
    Registered Users Posts: 251 ✭✭OMGeary


    Doctorhopeful wrote: »
    I got about 12ish, i saw how the quadratic would be 20/60 but the equation didn't work out so i had to use the quadratic formula. Is x=20 would you not have gotten a negative figure for A as A was 30 -2x at equil??

    No it wouldn't be minus 2 as they were all in the same ratio


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    #35
    Fiona G
    Registered Users Posts: 130 ✭✭Fiona G


    Whyyy do I look at these threads? Already seeing mistakes I made. Yet I'll still continue to read the thread...:p

    Was an okay paper. Bit trickier than other years in that there was a lot of reasoning to do instead of learned off stuff. Can't really predict my grade at all tbh. I loved the short questions and the rates question.


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    #36
    The_N4sir
    Registered Users Posts: 213 ✭✭The_N4sir


    Doctorhopeful wrote: »
    Ah **** i did X for both idk which is right... probably why it didn't work out so cleanly....

    You should still get a lot of the marks for the calculation anyway


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    #37
    Doctorhopeful
    Registered Users Posts: 200 ✭✭Doctorhopeful


    blue_velvet wrote: »
    What was the percentage yield for benzoic acid?I think I got around 43%

    I got 42.42% without rounding during the Q so i imagine anywhere around 42-43 is right


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    #38
    The_N4sir
    Registered Users Posts: 213 ✭✭The_N4sir


    Doctorhopeful wrote: »
    I got 42.42% without rounding during the Q so i imagine anywhere around 42-43 is right

    I definitely got that wrong I got around 60%:P
    Not having the equation threw me off for that part


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    #39
    DexterXX
    Registered Users Posts: 7 ✭DexterXX


    I got 50 overall for the equilibrium gas question. What did ye say for the effect of an increase in storage temperature on pressure?


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    #40
    Chocolalla
    Registered Users Posts: 26 ✭Chocolalla


    The_N4sir wrote: »
    Around -270 kJ/mol

    Got that as well :D


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    #41
    AlfaJack
    Registered Users Posts: 170 ✭✭AlfaJack


    DexterXX wrote: »
    What did ye say for the effect of an increase in storage temperature on pressure?

    Increase in temperature favours the forwards reacting and the forwards reaction produces the greater number of moles so the pressure would increase? That's what I said anyways...


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    #42
    Doctorhopeful
    Registered Users Posts: 200 ✭✭Doctorhopeful


    The_N4sir wrote: »
    I definitely got that wrong I got around 60%:P
    Not having the equation threw me off for that part

    Yeah that was indicative of how the paper was oddly worded! You had to read in the question that it was 1:1 took me ages to realise


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    #43
    Seanh966
    Registered Users Posts: 5 ✭Seanh966


    Doctorhopeful wrote: »
    Yeah that was indicative of how the paper was oddly worded! You had to read in the question that it was 1:1 took me ages to realise

    Pretty confident answer was 56 or 57% , several A1 candidates in my class got this


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    #44
    Dingle123
    Registered Users Posts: 7 ✭Dingle123


    Seanh966 wrote: »
    Pretty confident answer was 56 or 57% , several A1 candidates in my class got this

    I got about 57% aswell


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    #45
    Kerrypike
    Registered Users Posts: 6 ✭Kerrypike


    Dingle123 wrote: »
    I got about 57% aswell

    How was it supposed to be done?


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    #46
    Chickennuggets
    Registered Users Posts: 66 ✭✭Chickennuggets


    In the equilibrium question I got x=9.135. Any one esle get that


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    #47
    The_N4sir
    Registered Users Posts: 213 ✭✭The_N4sir


    Yeah I think the answer is 57 good few in my class got that


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    #48
    Seanh966
    Registered Users Posts: 5 ✭Seanh966


    Kerrypike wrote: »
    How was it supposed to be done?

    Grams of phenylmethanol Divided by molecular mass of phenylmethanol to get number of moles, ratio is one is to one so multiply this number by the molecular mass of benzoic acid for theoretical yield, put actual yield over theoretical for percentage yield


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    #49
    Chickennuggets
    Registered Users Posts: 66 ✭✭Chickennuggets


    Kerrypike wrote: »
    How was it supposed to be done?

    N = 6.35all over 108 (mr ) = 0.026 0.026 X 122(mr of benzoic acid ) = 3.172 1.83 all over 3.172 x100 = 57٪


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    #50
    Thebabyjesus
    Registered Users Posts: 9 ✭Thebabyjesus


    Got 57.7% for percentage, what did people get for grams pf crystalised sodium thiasulfate?


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    #51
    Kerrypike
    Registered Users Posts: 6 ✭Kerrypike


    Oh right I see.. I just used grams dang it


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    #52
    The_N4sir
    Registered Users Posts: 213 ✭✭The_N4sir


    Thebabyjesus wrote: »
    Got 57.7% for percentage, what did people get for grams pf crystalised sodium thiasulfate?

    I got around 34 g/l


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    #53
    Chickennuggets
    Registered Users Posts: 66 ✭✭Chickennuggets


    Thebabyjesus wrote: »
    Got 57.7% for percentage, what did people get for grams pf crystalised sodium thiasulfate?

    I got 3.95-4 it's probably wrong


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    #54
    Fiona G
    Registered Users Posts: 130 ✭✭Fiona G


    Chickennuggets wrote: »
    In the equilibrium question I got x=9.135. Any one esle get that

    Yeah I got this, we didn't take the size of the 10 litre vessel into account for the concentrations. Wonder how many marks we will lose?


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    #55
    Thebabyjesus
    Registered Users Posts: 9 ✭Thebabyjesus


    yeah im not too sure what it was, i ended up with around 17g?


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    #56
    Doctorhopeful
    Registered Users Posts: 200 ✭✭Doctorhopeful


    Seanh966 wrote: »
    Pretty confident answer was 56 or 57% , several A1 candidates in my class got this

    What did you get as the relative molecular masses?

    Ah **** i put the difference over the value i found, not the actual value over the thoretical!!! B ollocks, so i got 100 minus the right answer agh
    Wonder how many marks that'll be gone, agh, that's the second stupid mistake i've found and in two different questions :(


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    #57
    Alex Meier
    Closed Accounts Posts: 663 ✭✭✭Alex Meier


    57.6 % was the correct answer for the percentage yield


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    #58
    Chickennuggets
    Registered Users Posts: 66 ✭✭Chickennuggets


    Fiona G wrote: »
    Yeah I got this, we didn't take the size of the 10 litre vessel into account for the concentrations. Wonder how many marks we will lose?

    We didn't have to divide it because it said , in the container which was 10l anyway


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    #59
    otoolej2
    Registered Users Posts: 35 ✭otoolej2


    Seanh966 wrote: »
    Pretty confident answer was 56 or 57% , several A1 candidates in my class got this

    ye i got 57 point something. pretty sure its right, there will be a little wiggle room due to people rounding up to different numbers


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    #60
    OMGeary
    Registered Users Posts: 251 ✭✭OMGeary


    Chickennuggets wrote: »
    We didn't have to divide it because it said , in the container which was 10l anyway

    Kc is moles per litre


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    #61
    Seanh966
    Registered Users Posts: 5 ✭Seanh966


    Doctorhopeful wrote: »
    What did you get as the relative molecular masses?

    Ah **** i put the difference over the value i found, not the actual value over the thoretical!!! B ollocks, so i got 100 minus the right answer agh
    Wonder how many marks that'll be gone, agh, that's the second stupid mistake i've found and in two different questions :(

    Phenylmethanol 108
    Benzoic acid 122


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