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    Question 4 - 28 marks

    Naming:
    1,2-dibromoethane and 1-chloro - 2 bromoethane

    • Describe and explain the polarity of a carbon-halogen bond
    • Explain why CBr3Cbr3 has no overall dipole
    • Explain why Ch2BrCh2Cl has an overall dipole (5 marks)


    Technique: gas-liquid chromatography

    Explain why CH2BrCh2Br and CH2BrCH2Cl dissolove in each other:
    permanent dipole - permanent dipole between compounds. Strong Hydrogen bonds in water. For a compound to dissolve, must be stronger or equal to in strength to become hydrated and form ion-dipole bonds

    http://www.chemhume.co.uk/ASCHEM/Uni...gen_bromid.jpg

    electrophile - positive molecule, react by accepting a lone pair of electrons to form a new covalent bond

    Explain why Ch2ClCh2Br was formed, but Ch2ClCh2Cl was not formed in this reaction:??


    From CH2BrCh2Br to ethanedioic acid

    From the haloalkane Add water and form ethane1-2diol and then heat the intermediate under reflux with H+/Cr2o72- to form ethane dioic acid

    NMR question
    Structure: CH3CHBR2
    Peaks: 2 peaks so two different hydrogen enviornments
    Splitting of the peaks:
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    Could you post the paper up here if you've got a spare sec? Cheers mate.
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    What was the answer to the 4 mark calculation question?
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    Question 5 - 27 marks

    HPO42- Hydrogen phospahe(V) with phoshorus being +5

    Conjugate acid : H3Po4

    Ka = products - reactants

    Ph = 4.10

    Buffer solution and why important in human cells:
    Buffer solutions are solutions that main a constant PH on addition of a small amount of acid or alkali. Consists of a weak acid and its base and a weak base and one of its acid. Important in cells, as PH affects enzymes, thus it is vital a buffer soltion is in place, to keeps enzymes constant

    Explain what the buffer solution does on addition of acid:
    Moves to the left to absorb the acid. (2 marks - what else???)

    Ph of a buffer solution: 10... something lol

    Mass of solid NaH2Po4: (4 marks)

    Why 7.4cm3 of NaOh was required: there was 15.0cm of Nah2po4 - to reach the end point, 2 moles of Naoh of 7.5cm3 was required

    Error in the students argument: ??/


    Enthalpy diagram:
    exothermic reaction -
    top lines - gaseous ions
    then enthalp of hydration
    and then arrow down for exothermic and thus enthalpy of solution as the reaction was negative.
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    (Original post by ManPowa)
    Question 5 - 27 marks

    HPO42- Hydrogen phospahe(V) with phoshorus being +5

    Conjugate acid : H3Po4

    Ka = products - reactants

    Ph = 4.10

    Buffer solution and why important in human cells:
    Buffer solutions are solutions that main a constant PH on addition of a small amount of acid or alkali. Consists of a weak acid and its base and a weak base and one of its acid. Important in cells, as PH affects enzymes, thus it is vital a buffer soltion is in place, to keeps enzymes constant

    Explain what the buffer solution does on addition of acid:
    Moves to the left to absorb the acid. (2 marks - what else???)

    Ph of a buffer solution: 10... something lol

    Mass of solid NaH2Po4: (4 marks)

    Why 7.4cm3 of NaOh was required: there was 15.0cm of Nah2po4 - to reach the end point, 2 moles of Naoh of 7.5cm3 was required

    Error in the students argument: ??/


    Enthalpy diagram:
    exothermic reaction -
    top lines - gaseous ions
    then enthalp of hydration
    and then arrow down for exothermic and thus enthalpy of solution as
    the reaction was negative.
    Why was the KA products-reactants?
    It's usually KA= [H+][A-]/[HA]
    And that's how you get the right answer to the buffer question?
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    (Original post by ManPowa)
    Question 5 - 27 marks

    HPO42- Hydrogen phospahe(V) with phoshorus being +5


    Conjugate acid : H3Po4

    Ka = products - reactants

    Ph = 4.10

    Buffer solution and why important in human cells:
    Buffer solutions are solutions that main a constant PH on addition of a small amount of acid or alkali. Consists of a weak acid and its base and a weak base and one of its acid. Important in cells, as PH affects enzymes, thus it is vital a buffer soltion is in place, to keeps enzymes constant

    Explain what the buffer solution does on addition of acid:
    Moves to the left to absorb the acid. (2 marks - what else???)

    Ph of a buffer solution: 10... something lol

    Mass of solid NaH2Po4: (4 marks)

    Why 7.4cm3 of NaOh was required: there was 15.0cm of Nah2po4 - to reach the end point, 2 moles of Naoh of 7.5cm3 was required

    Error in the students argument: ??/


    Enthalpy diagram:
    exothermic reaction -
    top lines - gaseous ions
    then enthalp of hydration
    and then arrow down for exothermic and thus enthalpy of solution as the reaction was negative.
    For what I've highlighted in red, I think I may have missed it somehow!!! :/What was it asking?
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    (Original post by ManPowa)
    Question 3 - 20 marks

    molecular formula : C8 H8 02

    Equasion: phenylethanoic acid + calcium carbonate >>>> ????

    Curly arrow on the retrosynthetic analysis - From the Ch2 to the CO BOND

    Explain why synthons are not used to make the required compound.

    Nucleophilic substituition : Swap the CN with the Br and then leave the bromine as Br-

    Data sheets reageants : H+/H20/ with reflux


    Predict: As the forward reaction is exothermic, the equilbrium shifts to the left to absorb the heat and counteract the change. The equilibrium constant Kc, shall decrease..

    circled functional group : ether
    Functional in IAA BUT NOT IN THE OTHER TWO : Amine

    Wavenumber : O-H bond at a peak of 2500 - 3200 cm-1

    Circle just the carboxylic acid group.. this is the common pharmacophore in all 3 molecules

    Formula of the salt : someone has previously posted the exact answer

    Suggest why it is converted into a salt : I put to control the soil pH :/ lol and then i added salts are ionic which are water soluble.. Hmm... Answer people ..!!

    2 arguments :
    Inexpensive (cheap), use in small concentrations. anything else.. !!!
    For the part colour in red for H+, would been okay to give an example of an acid such as hydrochloric acid?
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    (Original post by feelbetter)
    For what I've highlighted in red, I think I may have missed it somehow!!! :/What was it asking?
    It was asking for the name of the compound and it's oxidation state... Just before the conjugate acid question? :]



    (Original post by feelbetter)
    For the part colour in red for H+, would been okay to give an example of an acid such as hydrochloric acid?
    I imagine so, a source of H+ should be okay :]
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    (Original post by SarahTM)
    Why was the KA products-reactants?
    It's usually KA= [H+][A-]/[HA]
    And that's how you get the right answer to the buffer question?
    Yeah its in the same context as Kc.. so basically it'll be:

    [H+] [HPO42-] / H2PO4-
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    For the one where you had to convert Ch2BrCH2br into the cooh. Was it 4 marks?
    Was this right?

    I then added potassium dichromate reflux... etc
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    (Original post by feelbetter)
    For what I've highlighted in red, I think I may have missed it somehow!!! :/What was it asking?
    It was asking for the systematic name and phosphorus oxidation state, it was the first question to question 5.
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    (Original post by SarahTM)
    It was asking for the name of the compound and it's oxidation state... Just before the conjugate acid question? :]





    I imagine so, a source of H+ should be okay :]
    I really can't remember it, for some reason, :/ I just hope I did it! and thanks
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    Didn't it ask for the oxidation state of HPO4- to catch you out?
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    (Original post by ManPowa)
    Yeah its in the same context as Kc.. so basically it'll be:

    [H+] [HPO42-] / H2PO4-
    Oh, so the - was meant to be a / ?
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    (Original post by tom108)
    For the one where you had to convert Ch2BrCH2br into the cooh. Was it 4 marks?
    Was this right?

    I then added potassium dichromate reflux... etc
    Yeah thats correct... and then the alcohol can go under reflux with potassium dichromate

    I did Water as the only reagent from haloalkane to the intermediate reagent. What do you think?
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    (Original post by SarahTM)
    Oh, so the - was meant to be a / ?
    yep, my bad lol
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    (Original post by ManPowa)
    It was asking for the systematic name and phosphorus oxidation state, it was the first question to question 5.
    Ah right, if I did it I think I would've got it, it really doesn't ring a bell!
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    (Original post by ManPowa)
    Yeah thats correct... and then the alcohol can go under reflux with potassium dichromate

    I did Water as the only reagent from haloalkane to the intermediate reagent. What do you think?
    I thought they were asking convert ethene to ethandioic acid?

    That is also correct isnt it ?
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    (Original post by ManPowa)
    yep, my bad lol
    Hehe, I'll let you off
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    Looking at all the answers from ManPowa I've definately lost 21 marks minimum (probably quite a bit more). I was hoping maybe for an a*, that's out of the window. The exam was awful and some mistakes i made were ridiculous, for example, i did the electron configuration of Sulfur using it's Ar. I revised a lot aswell.Hmph.
 
 
 
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