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    Hey guys, please can someone explain why B is the right answer? Also, if the sodium thiosulfate was added to the conical flask would the result be different or something? I always thought eg in iodine thiosulfate titration, the colour change forms a blue-black solution? Am I wrong here? So confused :s
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    (Original post by gabby07)
    Hey guys, please can someone explain why B is the right answer? Also, if the sodium thiosulfate was added to the conical flask would the result be different or something? I always thought eg in iodine thiosulfate titration, the colour change forms a blue-black solution? Am I wrong here? So confused :s
    Not sure why it's B to be honest :s! The only reason I can think of is that 0.05 goes one decimal place further than the volumetric flask so it matches the accuracy or something? I really don't know XD

    As for part b, it's colourless because sodium thiosulfate reduces iodine to iodide ions So once all the iodine has been reduced, a black to colourless colour change occurs.
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    (Original post by Don Pedro K.)
    Not sure why it's B to be honest :s! The only reason I can think of is that 0.05 goes one decimal place further than the volumetric flask so it matches the accuracy or something? I really don't know XD

    As for part b, it's colourless because sodium thiosulfate reduces iodine to iodide ions So once all the iodine has been reduced, a black to colourless colour change occurs.
    Sorry for the confusion - I forgot to say I was only talking about part b)! In the unit 4 exam, was the colour change the other way round?
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    (Original post by gabby07)
    Sorry for the confusion - I forgot to say I was only talking about part b)! In the unit 4 exam, was the colour change the other way round?
    Yes
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    (Original post by gabby07)
    Sorry for the confusion - I forgot to say I was only talking about part b)! In the unit 4 exam, was the colour change the other way round?
    Ohh okay aha And as far as I'm aware, the colour changes are the same! EDIT: I think you meant in the actual exam and yeah I do remember a question where it was reversed but this was because:

    In unit 4, I do remember questions were it involved persulfate ions, which oxidise iodide ions to iodine ions so in that case, when all the sodium thiosulfate in the mixture of sodium persulfate and potassium iodide has reacted, the colour change would be colourless to black. Check out the equations:

    Let's say we have a solution of persulfate ions, iodide ions, sodium thiosulfate ions and starch indicator.

    PERSULFATE IONS:

    S2O82- + 2I- --> 2SO42- + I2

    As you can see, the persulfate S2O82- ions oxidise iodide ions to iodine. If thiosulfate ions are also present in the solution however, they reduce any iodine formed immediately back to iodide ions:

    S2O32- + I2 --> S4O62- + 2I-.

    So initially, the solution stays colourless because any iodine formed gets reduced back to iodide ions straight away. Once the sodium thiosulfate has all reacted though, the only reaction occurring is:

    S2O82- + 2I- --> 2SO42- + I2

    Since you get iodine forming now without it being reduced back down to iodide ions, a colourless to black colour change occurs.
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    gabby07 When it's just thiosulfate ions in solution with iodine and iodide ions, the colour change is black to colourless at the end point because:

    S2O32- + I2 --> S4O62- + 2I-.

    Is the reaction that is occurring. So just before the end point, when the colour is a straw yellow, you add the starch so that the solution turns black (there's just a tiny bit of iodine left in the solution) and then you add the thiosulfate drop by drop until the black to colourless change occurs, which indicates that all the iodine has reacted.
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    Do the ial papers test the same content as the normal ones? Because they're really hard

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    (Original post by ab9826)
    Do the ial papers test the same content as the normal ones? Because they're really hard

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    Yes. :cry:
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    (Original post by Ayman!)
    Yes. :cry:

    The questions of Unit 5 are creepy!
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    Don Pedro K. you are the definition of a legend.
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    (Original post by ab9826)
    Do the ial papers test the same content as the normal ones? Because they're really hard

    Posted from TSR Mobile
    The unit 5 IAL papers seem to be insanely difficult...I feel sorry for you Ayman!
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    (Original post by gabby07)
    Don Pedro K. you are the definition of a legend.
    Hahahah thank you ;D!
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    (Original post by Don Pedro K.)
    The unit 5 IAL papers seem to be insanely difficult...I feel sorry for you Ayman!
    (Original post by sabahshahed294)
    The questions of Unit 5 are creepy!
    I'm literally on the verge of crying and having a mental breakdown because of this module.

    I am not kidding. :cry:

    Just aiming for a high B to maintain that A. :rofl:
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    (Original post by Ayman!)
    I'm literally on the verge of crying and having a mental breakdown because of this module.

    I am not kidding. :cry:

    Just aiming for a high B to maintain that A. :rofl:
    I'm on the verge to hit myself on the wall after reading this comment from you lol
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    (Original post by sabahshahed294)
    I'm on the verge to hit myself on the wall after reading this comment from you lol
    Why is that? 🤔 Have you done all the IAL papers? I've got Jan 15 (well, half of it), June 14, June 15 and Jan 16 to go.
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    (Original post by Ayman!)
    Why is that? 🤔 Have you done all the IAL papers? I've got Jan 15 (well, half of it), June 14, June 15 and Jan 16 to go.
    Did them for my school mocks. They were ugly I recall .
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    Can anyone explain how to do this one? Thanks!
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    (Original post by Mehodax)
    Can anyone explain how to do this one? Thanks!
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    Is the answer C?
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    The melting temperature is 136 for TiCl3

    How shall I know the structure of TiO2 and TiCl3 in order to answer this question ?
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    What the actual **** was IAL Jan 15?! I managed an A* just because of the low boundaries.
 
 
 
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