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

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13

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    #62
    Chickennuggets
    Registered Users Posts: 66 ✭✭Chickennuggets


    What did people get for the concentration of thiosulfate solution


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    #63
    otoolej2
    Registered Users Posts: 35 ✭otoolej2


    Chickennuggets wrote: »
    What did people get for the concentration of thiosulfate solution

    got something like 0.28 moles per litre, not sure doe.


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    #64
    Iamtheduchess
    Registered Users Posts: 46 ✭Iamtheduchess


    otoolej2 wrote: »
    got something like 0.28 moles per litre, not sure doe.

    Think mine could have been something similar.


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    #65
    emma35
    Registered Users Posts: 40 ✭emma35


    The_N4sir wrote: »
    That was a harder paper than I thought it would be. Was going for an A1 but i would be happy with a A2/B1 on that paper.

    Anyone else get 20 for the x value in question 11? Cant remember exactky but was a nice whole number

    yeah I got 20 ! please god it was right


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    #66
    Jason_H
    Registered Users Posts: 21 ✭Jason_H


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

    The equation was in a ratio of 1:2 so you have to take container size into account :(


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    #67
    expiiplus1
    Closed Accounts Posts: 71 ✭✭expiiplus1


    Why did you need to take the volume of the container into account? Surely that affects only pressure, while Kc is dependent completely on pressure.


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    #68
    expiiplus1
    Closed Accounts Posts: 71 ✭✭expiiplus1


    Sorry, I meant temperature


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    #69
    OMGeary
    Registered Users Posts: 251 ✭✭OMGeary


    expiiplus1 wrote: »
    Why did you need to take the volume of the container into account? Surely that affects only pressure, while Kc is dependent completely on pressure.

    KC is moles per Litre


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    #70
    smartz
    Registered Users Posts: 63 ✭✭smartz


    How much marks would you lose if you didn't take the volume into account?


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    #71
    YouKnowNothing
    Registered Users Posts: 25 ✭YouKnowNothing


    Thought it was a lovely exam, hopefully in course for a1
    Had a look over that q1 last night, it had only come up once in the past 13 years!


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    #72
    uzpuz
    Registered Users Posts: 15 ✭uzpuz


    The_N4sir wrote: »
    Around -270 kJ/mol

    I got -273


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    #73
    expiiplus1
    Closed Accounts Posts: 71 ✭✭expiiplus1


    Ah, I see. I hadn't seen that fact before.
    I did all three parts of that question out of nerves, so I'm not too worried about it :)


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    #74
    Bah_Humbug
    Registered Users Posts: 45 ✭Bah_Humbug


    Think I'll regret asking buuut why should distilled water be used instead of deionised Q1? :/


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    #75
    Iamtheduchess
    Registered Users Posts: 46 ✭Iamtheduchess


    Bah_Humbug wrote: »
    Think I'll regret asking buuut why should distilled water be used instead of deionised Q1? :/

    Things like Cl2 aren't ions but would have reacted with the KI to change iodine concentration so you would have had to distill them out.


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    #76
    expiiplus1
    Closed Accounts Posts: 71 ✭✭expiiplus1


    Deionised water contains covalent impurities


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    #77
    blue_velvet
    Registered Users Posts: 16 ✭blue_velvet


    Seanh966 wrote: »
    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

    I did exactly that just realised I put 1.38g ÷ 3.172g into calculator instead of 1.83g ÷ 3.172g...I'll only lose like 3 marks though??


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    #78
    MmmPancakes
    Registered Users Posts: 712 ✭✭✭MmmPancakes


    expiiplus1 wrote: »
    Deionised water contains covalent impurities

    Would I get marks if I said the dissolved solids could interfere with the reagents?


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    #79
    Alex Meier
    Closed Accounts Posts: 663 ✭✭✭Alex Meier


    blue_velvet wrote: »
    I did exactly that just realised I put 1.38g ÷ 3.172g into calculator instead of 1.83g ÷ 3.172g...I'll only lose like 3 marks though??

    You'll lose 1 mark


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    #80
    expiiplus1
    Closed Accounts Posts: 71 ✭✭expiiplus1


    Probably only a single mark


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    #81
    Jason_H
    Registered Users Posts: 21 ✭Jason_H


    YouKnowNothing wrote: »
    Thought it was a lovely exam, hopefully in course for a1
    Had a look over that q1 last night, it had only come up once in the past 13 years!

    It came up in 2007??


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    #82
    otoolej2
    Registered Users Posts: 35 ✭otoolej2


    what did people say for question 1 part A?


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    #83
    Chocolalla
    Registered Users Posts: 26 ✭Chocolalla


    Jason_H wrote: »
    It came up in 2007??

    I knew that one was going to come since the rest came up at least twice


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    #84
    d1234
    Registered Users Posts: 594 ✭✭✭d1234


    For the aspirin, where did people draw the circle / rectangle??


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    #85
    MmmPancakes
    Registered Users Posts: 712 ✭✭✭MmmPancakes


    otoolej2 wrote: »
    what did people say for question 1 part A?

    Iodine is brought into aqueous solution through the addition of potassium iodide to the conical flask, which liberates iodine when it reactions with the sodium thiosulfate


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    #86
    Bah_Humbug
    Registered Users Posts: 45 ✭Bah_Humbug


    Iamtheduchess wrote: »
    Things like Cl2 aren't ions but would have reacted with the KI to change iodine concentration so you would have had to distill them out.

    D'you think i'd get marks for saying deionised water contains dissolved gases and organic material that might affect the result? But didn't specifically mention a gas like Cl2? Depends on the marking scheme I suppose :(


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    #87
    MmmPancakes
    Registered Users Posts: 712 ✭✭✭MmmPancakes


    d1234 wrote: »
    For the aspirin, where did people draw the circle / rectangle??

    Circle around the carbon group above the benzene molecule, carbonyl group is C=O so to the right of it


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    #88
    smartz
    Registered Users Posts: 63 ✭✭smartz


    How much marks would you lose if you didn't take the volume into account in the equilibrium calculation.


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    #89
    Iamtheduchess
    Registered Users Posts: 46 ✭Iamtheduchess


    Bah_Humbug wrote: »
    D'you think i'd get marks for saying deionised water contains dissolved gases and organic material that might affect the result? But didn't specifically mention a gas like Cl2? Depends on the marking scheme I suppose :(

    Yeah I would think so, because I don't imagine many people knew the exact reason and you are technically correct 😊


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    #90
    Thebabyjesus
    Registered Users Posts: 9 ✭Thebabyjesus


    Appearance of phenylmethanol at room temp? Problems than can arise with A and D? and initial concentration of ethanoic acid?


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    #91
    otoolej2
    Registered Users Posts: 35 ✭otoolej2


    MmmPancakes wrote: »
    Iodine is brought into aqueous solution through the addition of potassium iodide to the conical flask, which liberates iodine when it reactions with the sodium thiosulfate

    ye, thats what i said. i forgot to mention potassium permangate, but i suppose that was'ent needed.


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