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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

  • View Poll Results: Which topic(s) are you finding most difficult?
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    15.95%
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    Group 2 & 7
    40.49%
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    Organic Chemistry - Alcohols and Halogenoalkanes
    39.26%
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    Didn't get an A or anything... but the exam was better than other Chemistry exams that I've sat in the past year. Didn't need an ambulance or anything afterwards

    But didn't do so well either I think I may have lost up to 30 marks. The multiple choice was particularly hard compared to past ones !
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    (Original post by posthumus)
    Didn't get an A or anything... but the exam was better than other Chemistry exams that I've sat in the past year. Didn't need an ambulance or anything afterwards

    But didn't do so well either I think I may have lost up to 30 marks. The multiple choice was particularly hard compared to past ones !
    30! :eek:
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    (Original post by airheadbuster)
    30! :eek:
    Yh just keeping it safe I don't do very well in Chemistry exams

    What do you guys recon grade boundaries will be like?

    EDIT: 2 question I completely missed out what could you do to chlorobutane whatever to turn it in alcohol with NaOH. & the one with ppm. Which is better than usual... where it's typical of me to leave half the paper blank
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    I know of like 6 marks that I've lost. But it was a very reaction based paper

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    (Original post by posthumus)
    Yh just keeping it safe I don't do very well in Chemistry exams

    What do you guys recon grade boundaries will be like?

    EDIT: 2 question I completely missed out what could you do to chlorobutane whatever to turn it in alcohol with NaOH. & the one with ppm
    PPM = (2.2/1000) x 10^6

    Remember the former one was about chlorobutane in water which means hydrolysis. Cl- ion will react with silver ion to form white ppt. Not sure though. :confused:
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    Do we want to start an unofficial markscheme? Disagree with me where you feel differently!

    I'm pretty sure the thiosulphate calculations went like this:
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8%

    And I think the percent error was 0.86%...

    The question with the mechanism was:
    =The solution would be dissolved in ethanol
    =It was elimination
    =The solution would be dissolved in water
    =It was the Sn2 mechanism

    The first section 2 question was Ba(s) + 2H2O (l) ---> Ba(OH)2 (aq) + H2 (g)
    The Ba changed oxidation number from 0 to +2
    And the H changed from +1 to 0 (though it stayed the same in the hydroxide)

    Then it was Ba(OH)2 + 2HCL ---> BaCl2 + 2H2O

    The difference would a white precipitate
    Because Barium sulphate is insoluble and Barium hydroxide is extremely soluble.

    Bonding questions:
    18 electrons
    London forces
    Both have London forces, though the one that's not F2 has permanent dipoles
    HF has hydrogen bonding, which is the strongest intermolecular force
    The Cl atom in HCl is too big to H bond, so doesn't form H bonds, so won't have the highest boiling point

    Questions following the little article
    (This one I'm totally not sure about!) It came out as 2200ppm, and 2200 > 60 so richer in bromine.
    More carbonate ions, less CO2, as more hydrogen carbonate ions were produced to use up the excess carbonate.
    Mechanism for global warming (what are the marks for here?!): Molecules with polar bond absorb IR which means that the Sun's rays are trapped in the atmosphere when they are reflected off the earth
    Assorted bull**** for the last 4 marker.

    The equilibria stuff
    (Again, not sure about this one) The HCl donated H+ ions to the equilibrium mixture, moving the equilibrium to the left and meaning that more bromine is formed rather than hydrolysed
    Temp increase it moved to the right because the forward reaction was endothermic and a temp increase favours the endothermic reaction
    Features of dynamic equilibrium, I put (not sure about this):
    -At a molecular level there is ceaseless change
    -To the naked eye, there is no change in the solution


    The multiple choice were (assorted answers, though as much in order as I can remember)
    SF6
    CCl4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    A for the titration multiple choice question
    The most common energy of the molecules
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    (Original post by geor)
    I put aqueous conditions and I think 2200...?
    I think grade boundaries will probably be high but lower than january


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    (Original post by airheadbuster)
    PPM = (2.2/1000) x 10^6

    Remember the former one was about chlorobutane in water which means hydrolysis. Cl- ion will react with silver ion to form white ppt. Not sure though. :confused:
    Ah damn I did that initially but then I thought ppm was 10^-6 & changed it... Oh well both were only 1 marks. But I lost more as well

    I think grade boundaries will be 62-64 / 80 for an A
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    (Original post by airheadbuster)
    Why does NaCl dissolve in water instead of alcohol?
    Why does fullerene dissolve in petrol while graphite and diamond do not?

    There was another question about carbon neutral that I don't think I answered right.
    What did you guys answer these 3?
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    I did an sn1 mechanism I'm not sure if it should have been sn2 it was a secondary haloalkanes :I


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    (Original post by TheBigGeek)
    Do we want to start an unofficial markscheme? Disagree with me where you feel differently!

    I'm pretty sure the thiosulphate calculations went like this:
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8%

    And I think the percent error was 0.86%...

    The question with the mechanism was:
    =The solution would be dissolved in ethanol
    =It was elimination
    =The solution would be dissolved in water
    =It was the Sn2 mechanism

    The first section 2 question was Ba(s) + 2H2O (l) ---> Ba(OH)2 (aq) + H2 (g)
    The Ba changed oxidation number from 0 to +2
    And the H changed from +1 to 0 (though it stayed the same in the hydroxide)

    Then it was Ba(OH)2 + 2HCL ---> BaCl2 + 2H2O

    The difference would a white precipitate
    Because Barium sulphate is insoluble and Barium hydroxide is extremely soluble.

    Bonding questions:
    18 electrons
    London forces
    Both have London forces, though the one that's not F2 has permanent dipoles
    HF has hydrogen bonding, which is the strongest intermolecular force
    The Cl atom in HCl is too big to H bond, so doesn't form H bonds, so won't have the highest boiling point

    Questions following the little article
    (This one I'm totally not sure about!) It came out as 2200ppm, and 2200 > 60 so richer in bromine.
    More carbonate ions, less CO2, as more hydrogen carbonate ions were produced to use up the excess carbonate.
    Mechanism for global warming (what are the marks for here?!): Molecules with polar bond absorb IR which means that the Sun's rays are trapped in the atmosphere when they are reflected off the earth
    Assorted bull**** for the last 4 marker.

    The equilibria stuff
    (Again, not sure about this one) The HCl donated H+ ions to the equilibrium mixture, moving the equilibrium to the left and meaning that more bromine is formed rather than hydrolysed
    Temp increase it moved to the right because the forward reaction was endothermic and a temp increase favours the endothermic reaction
    Features of dynamic equilibrium, I put (not sure about this):
    -At a molecular level there is ceaseless change
    -To the naked eye, there is no change in the solution


    The multiple choice were (assorted answers, though as much in order as I can remember)
    SF6
    CCl4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    A for the titration multiple choice question
    The most common energy of the molecules
    First one is correct.

    >Cl atom is too big.

    It will be the electronegativity difference between CL and H is not high enough to make hydrogen sufficiently &+. So, there will be no hydrogen bonding in HCl which means it will have lower boiling point.

    Features of dynamic equilibrium:

    1. The rate of forward reaction is equal to the rate of backward reaction.
    2. The concentration of the species on both sides of the reaction will be unchanged.

    IR:

    They absorb IR emitted from Earth's surface and re-radiates it back to Earth, contributing to global warming.
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    PS Reviewer
    I thought that was a decent paper. I talked alot of bull for the very last question.

    For the mechanism I did Sn1 as that is what secondary alcohols tend to go by.

    The multiple choice was fairly challenging.

    I reckon I lost about 10 to 12 marks.
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    (Original post by airheadbuster)
    What did you guys answer these 3?
    Why does NaCl dissolve in water instead of alcohol?
    Why does fullerene dissolve in petrol while graphite and diamond do not?

    There was another question about carbon neutral that I don't think I answered right.

    1) Because of hydration enthalpy
    2) can't remember options
    3) Got this one wrong... forgot to come back to it & the pesticide should have been taken into consideration
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    I think they would accept both mechanisms for the secondary haloalkane?
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    PS Reviewer
    For dynamic equilibrium I said that:

    There is no change to the concentrations of the products and reactants

    The rate of the forward reaction = rate of reverse
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    (Original post by airheadbuster)
    First one is correct.

    >Cl atom is too big.

    It will be the electronegativity difference between CL and H is not high enough to make hydrogen sufficiently &+. So, there will be no hydrogen bonding in HCl which means it will have lower boiling point.

    Features of dynamic equilibrium:

    1. The rate of forward reaction is equal to the rate of backward reaction.
    2. The concentration of the species on both sides of the reaction will be unchanged.

    IR:

    They absorb IR emitted from Earth's surface and re-radiates it back to Earth, contributing to global warming.
    Your "features of dynamic equilibrium" seems better than mine!
    And our teacher specifically said that the Cl atoms can't H bond because of its size...
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    (Original post by Goods)
    I did an sn1 mechanism I'm not sure if it should have been sn2 it was a secondary haloalkanes :I


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    I did SN1 too and I think we are right. They said "show the transfer of electrons with curly arrows" which probably meant heterolytic fission in C-Cl bond.
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    I think it was a tricky paper, especially the multiple choice but i think i went well for me (fingers crossed). I'm sure you all on here did fine too

    I know I lost 2 silly marks for sure, I put flame test for the second part of the testing question even though it asked to avoid using heat *doh*. But I swear all the questions were 1or 2 markers apart from the last one?
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    (Original post by TheBigGeek)
    Do we want to start an unofficial markscheme? Disagree with me where you feel differently!

    I'm pretty sure the thiosulphate calculations went like this:
    =0.00116
    =0.00058
    =0.0125
    =0.01192
    =13.8%

    And I think the percent error was 0.86%...

    The question with the mechanism was:
    =The solution would be dissolved in ethanol
    =It was elimination
    =The solution would be dissolved in water
    =It was the Sn2 mechanism

    The first section 2 question was Ba(s) + 2H2O (l) ---> Ba(OH)2 (aq) + H2 (g)
    The Ba changed oxidation number from 0 to +2
    And the H changed from +1 to 0 (though it stayed the same in the hydroxide)

    Then it was Ba(OH)2 + 2HCL ---> BaCl2 + 2H2O

    The difference would a white precipitate
    Because Barium sulphate is insoluble and Barium hydroxide is extremely soluble.

    Bonding questions:
    18 electrons
    London forces
    Both have London forces, though the one that's not F2 has permanent dipoles
    HF has hydrogen bonding, which is the strongest intermolecular force
    The Cl atom in HCl is too big to H bond, so doesn't form H bonds, so won't have the highest boiling point

    Questions following the little article
    (This one I'm totally not sure about!) It came out as 2200ppm, and 2200 > 60 so richer in bromine.
    More carbonate ions, less CO2, as more hydrogen carbonate ions were produced to use up the excess carbonate.
    Mechanism for global warming (what are the marks for here?!): Molecules with polar bond absorb IR which means that the Sun's rays are trapped in the atmosphere when they are reflected off the earth
    Assorted bull**** for the last 4 marker.

    The equilibria stuff
    (Again, not sure about this one) The HCl donated H+ ions to the equilibrium mixture, moving the equilibrium to the left and meaning that more bromine is formed rather than hydrolysed
    Temp increase it moved to the right because the forward reaction was endothermic and a temp increase favours the endothermic reaction
    Features of dynamic equilibrium, I put (not sure about this):
    -At a molecular level there is ceaseless change
    -To the naked eye, there is no change in the solution


    The multiple choice were (assorted answers, though as much in order as I can remember)
    SF6
    CCl4
    2-chlorobutane
    Potassium nitrate
    Ozone depletion
    A for the titration multiple choice question
    The most common energy of the molecules
    I'm pretty sure it was sn1 the other point with dynamic equilibrium is that concentrations of reactants are constant

    Was the alternative test a flame test? It said not using acid or by heating... But a flame test uses both it was all I could think of ....


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    (Original post by airheadbuster)
    I did SN1 too and I think we are right. They said "show the transfer of electrons with curly arrows" which probably meant heterolytic fission in C-Cl bond.
    Doesn't the C-Cl bond break heterolytically in sn2 mechanism as well?
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    (Original post by GCSE-help)
    I think they would accept both mechanisms for the secondary haloalkane?
    Yes, as it was a secondary halogenoalkane. I'm sure either will be fine!
 
 
 
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