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The Official Edexcel CH5 Revision Thread! (22/06/05 AM) watch

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    does anyone no if we are getting a synoptic question in unit 5 tomoro because biology shocked me yesterday wen they put half the paper as synoptic and i had no clue! Some of the past papers have a synoptic question at the end, some dont.
    Thanks
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    i was thinkin about this and i looked at last years unit 5 and there wasnt that much, it was basically drawing apparatus and knowing about hydrogen bonds etc
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    wat is the funtion of NaOH in deprotonation??
    what type of reaction is it from [Cr(H20)6]3+ to [Cr(OH)6]3-
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    the OH- ions abstract H+ ions from the liganded water molecules in a stepwise manner depending on the OH- ion concentration
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    Quick Q:
    Acidified K2Cr2O7 is frequently used as an oxidising agent in organic chemistry.
    i)Identify the product if it reacts with Butan-2-ol
    ii)Give the reagents and the observable result of a single reaction which is common to both butan-2-ol and the organic product in (i).

    THankz iN AdVanCe
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    In unit 5 chemistry the only synoptic bit is to do with organic so you need to know the organic from unit 2 and 4.
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    (Original post by meawinner1)
    I had a big debate about this with my teacher as she wasn't too sure of it herself, because I bought back my paper from january and they marked it wrong when I did not include water. You include water when it actually takes part in the reaction like with the reaction in the attachment, but usually you don't.
    Thats the equilibrium constant though, I think we're supposed to know how to differentiate between putting water in that or not but not in rate equations.
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    (Original post by meawinner1)
    In unit 5 chemistry the only synoptic bit is to do with organic so you need to know the organic from unit 2 and 4.
    Unit 5 includes synoptic from all modules, it's mainly the calculations, organic chem and kinetics from what i've seen but knowledge of past modules is assumed I think.

    I dont know why they have a synoptic element in unit 5 and a synoptic paper tbh, they do it in biology too. Only thing I can think of is that the questions are compeltely different in the actually synoptic paper and are more of a test of applying principles rather than memorising equations or whatever.
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    Can anyone show the polyaimde and polyester linkage?

    Thanks!
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    (Original post by mackin boi)
    Quick Q:
    Acidified K2Cr2O7 is frequently used as an oxidising agent in organic chemistry.
    i)Identify the product if it reacts with Butan-2-ol
    ii)Give the reagents and the observable result of a single reaction which is common to both butan-2-ol and the organic product in (i).

    THankz iN AdVanCe
    (i) butan-2-one because a secondary alcohol can only be oxidised this far
    (ii) both react with iodine and sodium hydroxide to give iodoform, a yellow precipitate with an aniseptic smell. the leftover of butan2one is propanoic acid, and the leftover of butan-2-ol is propan-1,1-diol I think...
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    (Original post by Paxi)
    Can anyone show the polyaimde and polyester linkage?

    Thanks!
    I don't understand the question...
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    (Original post by mackin boi)
    wat is the funtion of NaOH in deprotonation??
    what type of reaction is it from [Cr(H20)6]3+ to [Cr(OH)6]3-
    deprotination, all the way I think, in water there is an equilibrium of:

    2H2O <---> H(3)O+ + OH-

    when you add NaOH you are adding OH- ions and so driving equilibrium to the left, which removes H(3)O+ ions. There is also the equilibrium in the complex:

    [Cr(H2O)6]2+ + H2O <---> [Cr(H2O)5(OH)]+ + H3O+ (aq)

    And so as the amount of H3O+ falls in the first equilibrium it drives the second equilibrium to the right, producing more [Cr(H2O)5(OH)]+. There are subsequent equilibriums to form the tetraaquadihydroxychromium compound precipitaate and then even further to form triaquatrihydroxychromate, etc. all the way to hexahydroxychromate ions when enough NaOH is added.

    I think that's how it works. And the colour change would be: green solution, form green precipitate, which dissolves in excess to form dark green solution again.
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    (Original post by Paxi)
    Can anyone show the polyaimde and polyester linkage?

    Thanks!
    It's just like a normal ester bond or peptide bond, but the constituent residue at either end have free bonds. (and if you 'curl' the polymer around, each end should be able to make an ester or peptide link with each other - ie there should be no excessive atoms)
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    Im so screwed UNIT 5 is tommorow, and my knowledge on Chemistry is really crap cuz my attendence was crap! I need fifty percent what do you guys recommend I do tonight, my plan is too revise like hell all night, looking through my notes and reading up past paper questions....... I need to score 50 % cuz i need a D is chemistry, im on a D at the mo, AS C and unit 4 an E, i really havnt got a clue this year, should of payed attention
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    Polyester linkage.


    Polyamide linkage is ----CONH---
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    nice 1 paxi
 
 
 
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