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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by Jayqwe)
    Can anyone explain a condensation reaction with an example? That is one reaction I cant understand :/
    there aren't any for unit 2?
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    Hi, can somebody please list all the mechanisms for organic chemistry that we need to know for UNIT 2 , some seem to be in my notes and not in the cgp guide, I am getting confused

    Thanks in advance
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    (Original post by Goods)
    there aren't any for unit 2?
    Really? If so, then that is awesome
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    Hey guys. Is the reaction of bromine and water Br2 +h20 gives HBr and HBrO. (same for Cl).m
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    (Original post by felicity95)
    Hey guys. Is the reaction of bromine and water Br2 +h20 gives HBr and HBrO. (same for Cl).m
    You get an equilibrium.

    The products are HBr + HBrO
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    (Original post by Khurc003)
    Anyone know this one?? :/

    13 When solutions of iodine are titrated with aqueous sodium thiosulfate solution, Na2S2O3(aq),
    the thiosulfate ions are oxidized to

    A S2O4

    B S2O6

    C S2O8

    D S4O6

    all of these options are 2-
    S2O3 ions are oxidised to S4O6 ions. (D)

    Btw, do we have any mechanisms in unit 2 other than the SN1 and SN2 mechanisms?
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    When iodomethane is heated in a sealed tube with an excess of alcoholic ammonia, why can't ethylamine- CH3CH2NH2 be formed? :s


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    (Original post by geor)
    To be safe....
    - The mechanisms from unit 1 (electrophilic addition of bromine/hbr etc. to alkenes)
    Sn1/Sn2 of...
    - Nucleophilic substitution of OH-/water/ammonia to a halogenoalkane
    And... Elimination of halogenoalkanes to form a alcohol

    My teacher told me you wouldn't necessarily be asked to draw them out, but you may be asked about them so it's better to know them all to be safe rather than sorry!
    The main ones that you would definitely be expected to draw out are electrophilic addition of alkenes and nucleophilic substitution of OH-.
    Can you please explain what you mean by "elimination of halogenoalkanes to form an alcohol"?
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    can someone help to answer this please?

    In which of the following reactions is sulfuric(IV) acid, H2SO3, acting as an oxidizing
    agent?
    A 2NaOH + H2SO3------> Na2SO3 + 2H2O
    B 2FeCl3 + H2SO3 + H2O ------> 2FeCl2 + H2SO4 + 2HCl
    C 2H2S + H2SO3 ---------> 3H2O + 3S
    D H2SO3------> H2O + SO2

    The answer is C but why? I understand that an oxidizing agent accepts electrons and gets reduced so it means it gains electrons. How would this be demonstrated in the equation?

    Thanks
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    (Original post by acer0951)
    can someone help to answer this please?

    In which of the following reactions is sulfuric(IV) acid, H2SO3, acting as an oxidizing
    agent?
    A 2NaOH + H2SO3------> Na2SO3 + 2H2O
    B 2FeCl3 + H2SO3 + H2O ------> 2FeCl2 + H2SO4 + 2HCl
    C 2H2S + H2SO3 ---------> 3H2O + 3S
    D H2SO3------> H2O + SO2

    The answer is C but why? I understand that an oxidizing agent accepts electrons and gets reduced so it means it gains electrons. How would this be demonstrated in the equation?

    Thanks
    Look at oxidation numbers...

    in H2S .... S has oxidation number -2 (two H+ ... +1 x 2= +2 ... therefore S is in -2 state)

    Then look at it on the right hand side... it's oxidation number is 0. The oxidation number has increased from -2 to 0. Therefore Sulfur has been oxidized and sulfuric acid is acting as an oxidizing agent there (while itself has been reduced).

    Hope that helps
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    (Original post by acer0951)
    can someone help to answer this please?

    In which of the following reactions is sulfuric(IV) acid, H2SO3, acting as an oxidizing
    agent?
    A 2NaOH + H2SO3------> Na2SO3 + 2H2O
    B 2FeCl3 + H2SO3 + H2O ------> 2FeCl2 + H2SO4 + 2HCl
    C 2H2S + H2SO3 ---------> 3H2O + 3S
    D H2SO3------> H2O + SO2

    The answer is C but why? I understand that an oxidizing agent accepts electrons and gets reduced so it means it gains electrons. How would this be demonstrated in the equation?

    Thanks
    Do the oxidation state for sulphur and you will see (if i havent made a mistake) that it goes from being +4 in H2SO3 to being 0 at S. so it has gained electrons...


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    Thank you! Good luck with the test
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    So has anyone got any predictions as to what might come up?

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    (Original post by JonnyD)
    So has anyone got any predictions as to what might come up?

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    There will definitely be some chemistry. I think there's likely to be quite a lot on the applications of core chemistry. Other than that anything on the syllabus might come up

    oh come on people... lighten up this was obviously a joke

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    Hi Guys, do you know how much detail about back titrations and standard solution preparation we need to know? There's always questions on them involving calculations and accuracy analysis, but can we get asked to describe how to carry them out? Thanks
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    (Original post by Goods)
    There will definitely be some chemistry. I think there's likely to be quite a lot on the applications of core chemistry. Other than that anything on the syllabus might come up


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    Oh you cheeky little noodle
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    [June 2009]
    13)The bonding in gaseous hydrogen halides is best described as
    A. mainly covalent with an increasing tendency towards ionic as you go down the
    group.
    B. mainly covalent with an increasing tendency towards ionic as you go up the
    group.
    C. mainly ionic with an increasing tendency towards covalent as you go down the
    group.
    D. mainly ionic with an increasing tendency towards covalent as you go up the
    group.

    Why is the answer B and not A?
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    (Original post by GCSE-help)
    Hi Guys, do you know how much detail about back titrations and standard solution preparation we need to know? There's always questions on them involving calculations and accuracy analysis, but can we get asked to describe how to carry them out? Thanks
    We need to know that to prepare a solution. For titration you take a known volume and add it to a volumetric flask make it up to the mark with distilled water then neutralise it with 0.1 molar acid or alkali


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    (Original post by SKK94)
    [June 2009]
    13)The bonding in gaseous hydrogen halides is best described as
    A. mainly covalent with an increasing tendency towards ionic as you go down the
    group.
    B. mainly covalent with an increasing tendency towards ionic as you go up the
    group.
    C. mainly ionic with an increasing tendency towards covalent as you go down the
    group.
    D. mainly ionic with an increasing tendency towards covalent as you go up the
    group.

    Why is the answer B and not A?
    Ionic character occurs when there is a noticeable difference in electronegativeity fluorine and hydrogen have the largest difference therefore are most ionic and so it is covalent and increasingly ionic up the group


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    (Original post by Goods)
    Ionic character occurs when there is a noticeable difference in electronegativeity fluorine and hydrogen have the largest difference therefore are most ionic and so it is covalent and increasingly ionic up the group


    Posted from TSR Mobile
    Thanks
    Could another reason be that there is more polarisation of the bond down the group, hence ionic character is greater at the top?
 
 
 
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