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OCR chemistry unit 1 Friday 21st May 2010 watch

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    (Original post by steph_v)
    No, it wouldn't be pale green. Br2 is orange in water and organic solvents. CL2 would be pale green.

    Edit: At least, I think it is. I'm doubting myself now!
    Relax, it was definitely orange.
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    (Original post by steph_v)
    No, it wouldn't be pale green. Br2 is orange in water and organic solvents. CL2 would be pale green.

    Edit: At least, I think it is. I'm doubting myself now!
    No. You're right. He's wrong. Wrong, wrong, wrong.

    Aqueous Chloride ions are COLOURLESS. When they are by themselves as Diatomic molecules in either water or an organic solvent is when they become PALE GREEN.

    Because the Bromine does NOT displace the Chlorine, it is the BROMINE that is dissolved in the organic solvent, which is why it turned orange.

    (Original post by justDannyboy)
    It gave you the mass of the impure caustic soda, and you worked out the mol. You can then work out the mr, and as you know pure caustic soda is NaOH(S), which has a MR of 40, and the other one was like 40.7,You can find the percentage purity by mass, by dividing the two, and mulitplying by 100.

    It said "compostition BY MASS".
    It gave you the mass of the impure caustic soda, but it gave you the MOLES of the NaOH because you derived how much of it had reacted from the moles of HCL that had reacted. (1.98[or whatever it was] out of 2 grams). You were NEVER given the molar amount of the impure caustic soda. End. It was a simple percentage purity question, and even it WAS composition by mass it would be the same answer.
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    (Original post by steph_v)
    No, it wouldn't be pale green. Br2 is orange in water and organic solvents. CL2 would be pale green.

    Edit: At least, I think it is. I'm doubting myself now!
    I'm pretty sure its orange; when you bubble the Br2 through the organic solvent (cyclohexane), an addition reaction occurs to from 1,2 dibromohexane; thus giving an orange layer.
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    (Original post by Mr van der WAALs)
    I'm pretty sure its orange; when you bubble the Br2 through the organic solvent (cyclohexane), an addition reaction occurs to from 1,2 dibromohexane; thus giving an orange layer.
    That's actually not true. Bromine doesn't react with cyclohexane at all(except under UV light). I think you're getting a bit muddled. When Bromine reacts with CyclohexENE, Bromine water/ Bromine is discoloured because it forms 1,2-dibrocyclohexane (which is colourless).

    When Bromine is introduced to Cyclohexane, the non-polar nature of Cyclohexane induces dipoles in Bromine. I think the reason it changes colour is just the way the light acts through a new medium.
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    bromine cannot displace chlorine, because chlorine is more reactive and a more powerfull oxidising agent, therefor bromine would be present as Br2 which is orange in the organic solvent. they were three reactions the question gave 1st was chlorine with idoine, which is purple, second bromine with chlorine, which is orange, and the third im sure it was chlorine with bromine, and coz bromine cant displace chlorine, the colour would be orange.
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    (Original post by Mr van der WAALs)
    I'm pretty sure its orange; when you bubble the Br2 through the organic solvent (cyclohexane), an addition reaction occurs to from 1,2 dibromohexane; thus giving an orange layer.
    i agree with u
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    okay 3 things:
    1) i hated that % composition question.. i got 9.84% and i KNEW that i had to do something about the scaling but the stupid lady overlooking the exam was standing over my head and stressing: do NOT write anything else. put your pen DOWN. lol needless to say i had left the qtn till last coz it sort of confused me when i first read it. My question is, if the answer was 98.4% do i at least get 2 marks? total marks awarded was 3.. damn at least 1 mark? id get 1 right? preferrably 2 though!

    okay and 2) for the halogen question my colour for the last one i put pale green. at first i had put orange but i re-read it and they were bubbling br2 into a solution of cl- ions,, therefore the colour originally would have been pale green in the organic layer (due to the cl- ions) and since br2 does not displace chlorine as its a weaker oxidising agent the colour would remain pale green, it wouldnt be orange.. so yh, please explain if that was wrong

    and 3) i cant actually remember the exact question.. it came after determining the shape of BF3 something about permanent dipoles? What did people put down for that? i talked about electronegativity, but im not sure i was actually answering the qtn.. :s
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    (Original post by Flame_Thrower)
    okay 3 things:
    1) i hated that % composition question.. i got 9.84% and i KNEW that i had to do something about the scaling but the stupid lady overlooking the exam was standing over my head and stressing: do NOT write anything else. put your pen DOWN. lol needless to say i had left the qtn till last coz it sort of confused me when i first read it. My question is, if the answer was 98.4% do i at least get 2 marks? total marks awarded was 3.. damn at least 1 mark? id get 1 right? preferrably 2 though!

    okay and 2) for the halogen question my colour for the last one i put pale green. at first i had put orange but i re-read it and they were bubbling br2 into a solution of cl- ions,, therefore the colour originally would have been pale green in the organic layer (due to the cl- ions) and since br2 does not displace chlorine as its a weaker oxidising agent the colour would remain pale green, it wouldnt be orange.. so yh, please explain if that was wrong

    and 3) i cant actually remember the exact question.. it came after determining the shape of BF3 something about permanent dipoles? What did people put down for that? i talked about electronegativity, but im not sure i was actually answering the qtn.. :s
    1) Calculating the moles of both NaOH and H2SO4 will, I would beleive give you two marks; the last mark would be to distinguish the ratio between 25 and 250cm^3 and finally to calculate the %


    2) It is orange as the final colour; at first I put pale green but if you read the question carefully you should realise that when Br is bubbled through the solution, it cannot displace the Cl, hence it reacts with the organic colvent (cyclohexane) to form an ORANGE layer, of 1,2 dibromohexane.

    3) I did refer to electronegativity; and how F is more electronegative hence attracting the electrons more creating a difference in charge density, creating a dipole
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    (Original post by Mr van der WAALs)
    1) Calculating the moles of both NaOH and H2SO4 will, I would beleive give you two marks; the last mark would be to distinguish the ratio between 25 and 250cm^3 and finally to calculate the %


    2) It is orange as the final colour; at first I put pale green but if you read the question carefully you should realise that when Br is bubbled through the solution, it cannot displace the Cl, hence it reacts with the organic colvent (cyclohexane) to form an ORANGE layer, of 1,2 dibromohexane.

    3) I did refer to electronegativity; and how F is more electronegative hence attracting the electrons more creating a difference in charge density, creating a dipole
    awww maannn!! at least the elecronegativity, i think i got right. For the % one i took the moles of NaOH, found the mass, divided that mass with the impure sample provided (2.0g i believe) and err multiplied by 100. Crap, that doesnt sound like the working out they'd be looking for but in reference to the colours.. you know the colour they provided? the solution was orange when Br2 was bubbled through I- ions.. (i think that was correct) and the colour they had typed was orange.. as Br2 would displace the I- they didnt say it was purple/ violet due to I2 formed? Im still confused. :eek3:
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    (Original post by Flame_Thrower)
    awww maannn!! at least the elecronegativity, i think i got right. For the % one i took the moles of NaOH, found the mass, divided that mass with the impure sample provided (2.0g i believe) and err multiplied by 100. Crap, that doesnt sound like the working out they'd be looking for but in reference to the colours.. you know the colour they provided? the solution was orange when Br2 was bubbled through I- ions.. (i think that was correct) and the colour they had typed was orange.. as Br2 would displace the I- they didnt say it was purple/ violet due to I2 formed? Im still confused. :eek3:
    The first box was purple/voilet; when the Iodine is displaced the ions form a purple layer; the second box was done for us, the orange layer forms as the Br is displaced by the Cl. However the last box was again orange, the Br cannot displace the Cl ions therefore forming an orange layer as it reacts with the solution; just like if iodine was bubbled through Cl ions a brown solution would form.
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    (Original post by Mr van der WAALs)
    The first box was purple/voilet; when the Iodine is displaced the ions form a purple layer; the second box was done for us, the orange layer forms as the Br is displaced by the Cl. However the last box was again orange, the Br cannot displace the Cl ions therefore forming an orange layer as it reacts with the solution; just like if iodine was bubbled through Cl ions a brown solution would form.
    Aaaaaah!! Damnit that makes sense!!! Noooo!!! The worst part is that i WROTE orange at first but you know when you quickly change things before you hear the dreaded.. put your pens down now please..? thats what i did *cries* LOOOL and i thought myself quite clever too, mentally patting myself on the back for spotting things in the nick of time What. An. Idiot. :yep: And i call myself an A2 student. Damn!!
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    people dont stress, uv got chem 2 unit to worry about than a retake, which is worth 50% of As
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    does someone have a link to the this may21st f321 ocr chem paper?
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    (Original post by Flame_Thrower)
    Aaaaaah!! Damnit that makes sense!!! Noooo!!! The worst part is that i WROTE orange at first but you know when you quickly change things before you hear the dreaded.. put your pens down now please..? thats what i did *cries* LOOOL and i thought myself quite clever too, mentally patting myself on the back for spotting things in the nick of time What. An. Idiot. :yep: And i call myself an A2 student. Damn!!
    Lol I know how you feel; I made a few silly mistakes whislt doing the paper. I was hoping for 90/90 UMS but I doubt if I will get it; but hopefully I supressed my previous score of 73/90. :o:
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    (Original post by Mr van der WAALs)
    Lol I know how you feel; I made a few silly mistakes whislt doing the paper. I was hoping for 90/90 UMS but I doubt if I will get it; but hopefully I supressed my previous score of 73/90. :o:
    wot dyu usually need in this paper to get 90/90 ums?
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    lol u need full 60 marks mate
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    (Original post by StephanRamone)
    i sed 2nd 3rd 10th and 11th like you, but i also put 12th and 13th as the question sed all of the s sub-shell ionisations not just the ones in the table
    well i just anwsered the question by refering to how many electrons were in s shells in the table they provided, that table had meaning
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    (Original post by FoOtYdUdE)
    wot dyu usually need in this paper to get 90/90 ums?
    Usually 60/60 raw for 90/90 UMS unfortunatly; however it was it might be lower this summer. Apart from the orbital definition I don't think I dropped a mark :rolleyes:
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    Oh jesus.

    I just realised, with the Na2CO3 question - ... I did the equation all right, explained that the solid dissolves, etc, but then I put that hydrogen gas effervesces (I'd done so many past papers where this question came up and it was nearly ALWAYS hydrogen, I guess that kinda drilled it into me a little too much).

    That's at least one mark gone.
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    It remains orange as there is no displacment reaction
 
 
 
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