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    OGHHH, YES, SAME!!! And now i am freaking out over this. I don't think i will ever get over yesterday. Never.
    :emo: it's so depressing.

    On the bright side I'm pretty much guaranteed a C.
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    (Original post by sportycricketer)
    Just to confirm the colour changes for the thiosulphate, copper and iodine reaction..

    Is it Brown to Colourless/Straw?
    I think so yeah, just checked.

    Do you have any tips? Omg im dreading this exam!!!! I dont know whether to go through theory or papers. Papers i think
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    (Original post by viksta1000)
    which one of the reasons why you have to use born haber to find LE...and because its impossible to measure directly
    ahh ok, but sure the standard enthalpy of hydration also needs to have gaseous ions under standard conditions and this is needed to work out the lattice enthalpy?!
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    (Original post by sportycricketer)
    Just to confirm the colour changes for the thiosulphate, copper and iodine reaction..

    Is it Brown to Colourless/Straw?
    yess the iodine has a brown colour, so the CuI precipitate which is in fact white.. appears to be brown
    When thiosulphate reacts with the iodine, its colour 'weakens' and when it gets to a much paler, straw coloured shade, we add starch, this turns blue/black.
    When reaching the end point.. the blue/black disappears v. quickly to give a colourless solution
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    (Original post by HEC14)
    yess the iodine has a brown colour, so the CuI precipitate which is in fact white.. appears to be brown
    When thiosulphate reacts with the iodine, its colour 'weakens' and when it gets to a much paler, straw coloured shade, we add starch, this turns blue/black.
    When reaching the end point.. the blue/black disappears v. quickly to give a colourless solution
    where does the white precipitate go?
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    SOMEONE PLEASE GIVE ME A LIST OF THE COLOURS OF COMPOUNDS/TRANSITION METALS I NEED TO KNOW! I've tried looking through the thread to see if anyone bad posted any but can't find any!
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    (Original post by HEC14)
    yess the iodine has a brown colour, so the CuI precipitate which is in fact white.. appears to be brown
    When thiosulphate reacts with the iodine, its colour 'weakens' and when it gets to a much paler, straw coloured shade, we add starch, this turns blue/black.
    When reaching the end point.. the blue/black disappears v. quickly to give a colourless solution

    (Original post by Rosi M)
    I think so yeah, just checked.

    Do you have any tips? Omg im dreading this exam!!!! I dont know whether to go through theory or papers. Papers i think

    (Original post by ruby321)
    Not colourless, its pale yellow/straw I think and theres a white ppt
    Thanks everyone! So basically if a question comes up about the colour change we can either say:

    with starch: blue/black to colourless
    without starch: brown to pale straw

    Is that correct? and do we need to mention about the white ppt anywhere or is that included in the statement above?
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    (Original post by ruby321)
    where does the white precipitate go?
    i presume it dissolves when we proceed to titrate with the thiosulphate
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    (Original post by ruby321)
    ahh ok, but sure the standard enthalpy of hydration also needs to have gaseous ions under standard conditions and this is needed to work out the lattice enthalpy?!
    they'll tell you one of them in the question and ask you to work the other out using (clockwise arrows = anticlockwise arrow)
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    (Original post by iSomething)
    Hi, im stuck on this question from the OCR practice question section about redox equations, I'm having trouble balancing it as I cant seem to arrive at the answer they have at the back of the book:

    "Aqueous thiosulfate ions, S2O3^2-, are oxidised to sulfate (VI) ions, SO4^2-, by chlorine gas, which is reduced to chloride ions." Use oxidation states to construct a redox equation."

    Here's my attempt but im lost as to what I should be doing to the O atoms (I could add 2H2O but as it would solve the 2O atoms and could balance with 4H+ ions on other side but the book says its 5H2O and 10H+ on other side. How is that possible unless im being really stupid.

    When you do a redox equation, before you work out oxidation states you must make sure the things being redoxed are balanced. You haven't done that for Cl in the first equation. Try it again, this time balancing Cl
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    (Original post by sportycricketer)
    Thanks everyone! So basically if a question comes up about the colour change we can either say:

    with starch: blue/black to colourless
    without starch: brown to pale straw

    Is that correct? and do we need to mention about the white ppt anywhere or is that included in the statement above?
    I don't think that's entirley correct,
    They are two different steps,
    The addition of starch makes the end point more clear..
    When the colour of 'straw' is still present, it means that the iodine is still present, however the point at which all the iodine has reacted will be too difficult to measure as the colour change is minuscule and hard to see, hence we add the starch to improve accuracy
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    Can anyone tell me why we ignore [H2O] when doing a Kstab equation?
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    (Original post by SmartFool)
    SOMEONE PLEASE GIVE ME A LIST OF THE COLOURS OF COMPOUNDS/TRANSITION METALS I NEED TO KNOW! I've tried looking through the thread to see if anyone bad posted any but can't find any!
    I'll give it a go to test my revision!!! (bad motives, i know )

    Vanadium 2+ purple 3+ green 4+ blue 5+ yellow
    Chromium 3+ green +6 orange
    Iron 2+ green +3 yellow
    Cobalt 2+ pink
    Manganese +7 purple(dark) +2 pale pink, almost colourless
    Copper 2+ blue

    Copper hydroxide is pale blue precipitate
    Iron hydroxide (2+) is a green precipitate (rusty at surface)
    Iron hydroxide (3+) is a brown precipitate
    Cobalt hydroxide is a blue precipitate

    Please correct me someone 'cos i dont trust myself at all. Someone add anything 'cos im sure i havent put everything down. This is all i can remember
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    (Original post by student777)
    Can anyone tell me why we ignore [H2O] when doing a Kstab equation?
    Its because its dissolved in H20 and therefore the concentration of H20 is constant so we just ignore it.
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    (Original post by student777)
    Can anyone tell me why we ignore [H2O] when doing a Kstab equation?
    because H2O is in a very high conc. i.e. it can be considered as constant in all cases so it is ignored
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    (Original post by student777)
    Can anyone tell me why we ignore [H2O] when doing a Kstab equation?
    because almost everything is dissolved in water.. so basically that is saying everything is (aq).. Meaning water itself is large in excess.
    Alsooo.. it's concentration is virtually constant..
    So we don't need to bother with it
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    (Original post by Rosi M)
    I'll give it a go to test my revision!!! (bad motives, i know )

    Vanadium 2+ purple 3+ green 4+ blue 5+ yellow
    Chromium 3+ green +6 orange
    Iron 2+ green +3 yellow
    Cobalt 2+ pink
    Manganese +7 purple(dark) +2 pale pink, almost colourless
    Copper 2+ blue

    Copper hydroxide is pale blue precipitate
    Iron hydroxide (2+) is a green precipitate (rusty at surface)
    Iron hydroxide (3+) is a brown precipitate
    Cobalt hydroxide is a blue precipitate

    Please correct me someone 'cos i dont trust myself at all. Someone add anything 'cos im sure i havent put everything down. This is all i can remember
    I don't think you need to know the colour of every single ion... just the ppt. with OH- reactions and ligand substitution...
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    (Original post by Rosi M)
    I'll give it a go to test my revision!!! (bad motives, i know )

    Vanadium 2+ purple 3+ green 4+ blue 5+ yellow
    Chromium 3+ green +6 orange
    Iron 2+ green +3 yellow
    Cobalt 2+ pink
    Manganese +7 purple(dark) +2 pale pink, almost colourless
    Copper 2+ blue

    Copper hydroxide is pale blue precipitate
    Iron hydroxide (2+) is a green precipitate (rusty at surface)
    Iron hydroxide (3+) is a brown precipitate
    Cobalt hydroxide is a blue precipitate

    Please correct me someone 'cos i dont trust myself at all. Someone add anything 'cos im sure i havent put everything down. This is all i can remember
    also cobalt hydroxide is a pink precipitate
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    (Original post by ruby321)
    I don't think you need to know the colour of every single ion... just the ppt. with OH- reactions and ligand substitution...
    I've seen them ask single ions in a few old spec papers so i went and learnt a few but your right, doubt they would ask that for new spec.
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    (Original post by HEC14)
    i presume it dissolves when we proceed to titrate with the thiosulphate
    hmm yeah it probably does, I remember doing the titration and there definitly was no white ppt at the end...
 
 
 
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