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OCR Salters Chemistry F335 12th June 2013 Exam revision thread Watch

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    For the use of hydrogen could you have a blowing agent? :confused:
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    (Original post by JG17)
    I wrote that too. I'm fairly sure it was as I think you had to work backwards from the second equation, where the hydrogen ions increased so the POE shifted to the products and that shifted the POE on the first equation to the left?
    I did that as well, because there weren't any hydrogen ions in the first equation so logically I thought we had to work backwards.


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    (Original post by suncake)
    Classifying reactions:

    First one was about isocyanate synthesis - "What type of reaction is step 2?" A single H was removed, as far as I could tell... I put elimination, no idea what the actual answer is

    Second one was about the polymers - addition, as no small molecule eliminated.



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    Isnt the polymer Condensation polymerisation? Because h2o is lost

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    (Original post by Ikklemini)
    Isnt the polymer Condensation polymerisation? Because h2o is lost

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    h2o isn't lost, the H from the alcohol binds to the nitrogen to make a secondary amide.
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    (Original post by ells-13)
    for the reflectance spectrum sketch was it 2 humps for blue and red that were high percentages???
    was it two peaks...i thought it was a peak at roughly at 600nm
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    (Original post by hayleyvictoria)
    I put that too!
    that's not balanced. I put (HCOO)2Ca. It's like a sodium ethanoate salt but since Ca is 2+ i figured it's dimethanoate.
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    can someoneeee make a unofficial mark scheme PRETTY please
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    (Original post by ells-13)
    for the reflectance spectrum sketch was it 2 humps for blue and red that were high percentages???
    Swear it said the colour blue was something 0%???


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    How did everyone find the paper? I feel like I've blown my A out of the window

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    Does anyone know the answer to and how to do the last question (the calculation on iodine number)?
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    now i'm confused what did everyone get for the reflectance spectrum?!!!!!!!!!!!!!!!!!!!!!!
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    (Original post by Sujman)
    now i'm confused what did everyone get for the reflectance spectrum?!!!!!!!!!!!!!!!!!!!!!!
    i'm not sure if it's correct but: Since we know the colour is "titanium yellow", and we know that the colour we see is the colour reflected i put a curve with maximum at the middle (yellow) going down to 0 at the red and blue ends.
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    (Original post by aWildPidgey)
    Does anyone know the answer to and how to do the last question (the calculation on iodine number)?
    The answer was like 180g. The solution is as follows:

    Moles of thiosulfate = concentration of thiosulfate x volume of thiosulfate
    Moles of I2 UNREACTED = moles of thiosulfate / 2

    Moles of I2 REACTED = total moles of I2 (given) - Moles of I2 Unreacted

    Moles of I2 reacted x Mr of I2 = Mass of I2 Reacted with 0.2g.
    Mass of I2 Reacted calculated above is for 0.2g, hence

    Iodine Number = Mass of I2 Reacted x 500.
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    (Original post by calmpeach)
    for the very last bit, did you divide the Ka by 2 and -log'ed it??
    Yurp.
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    (Original post by Mattywooda)
    Yurp.
    Oh nooo, I multiplied it by 2 I think (((

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    (Original post by badatgow)
    i'm not sure if it's correct but: Since we know the colour is "titanium yellow", and we know that the colour we see is the colour reflected i put a curve with maximum at the middle (yellow) going down to 0 at the red and blue ends.
    me tooooooo
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    (Original post by badatgow)
    i'm not sure if it's correct but: Since we know the colour is "titanium yellow", and we know that the colour we see is the colour reflected i put a curve with maximum at the middle (yellow) going down to 0 at the red and blue ends.
    I did that too!
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    I found the paper overall pretty tough, but i'm confident i've done pretty well because I managed to finish quite fast and had plenty of time (like 40 mins) thankfully to check over everything a couple of times. While I was checking the paper I felt a lot better about my chances, because in hindsight most of the questions were relatively straightforwards. While doing the questions for the first time I felt like I was struggling a lot, but that's probably due to seeing unusual thinks like isoprenes etc.

    The interesting question IMO was the one about the calcium carbonate shells. My reasoning was that, increasing acidity increases [H+], so second equation equilibrium concentration shifts to the right. This increases concentration of [HCO3-]. I figured this would increase the concentration of [CO3 2-] in the first equation, so equilibrium would shift to the left to oppose the change. As a result, calcium carbonate concentration would increase and the shell thickness would increase. However, writing that down made me feel like a mug the entire time because i'm pretty sure if you pour acid on calcium carbonate it would just dissolve...but I couldn't see the chemistry to disagree with me. Oh well, only 2 marks if i'm wrong anyways.
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    (Original post by badatgow)
    The answer was like 180g. The solution is as follows:

    Moles of thiosulfate = concentration of thiosulfate x volume of thiosulfate
    Moles of I2 UNREACTED = moles of thiosulfate / 2

    Moles of I2 REACTED = total moles of I2 (given) - Moles of I2 Unreacted

    Moles of I2 reacted x Mr of I2 = Mass of I2 Reacted with 0.2g.
    Mass of I2 Reacted calculated above is for 0.2g, hence

    Iodine Number = Mass of I2 Reacted x 500.
    WHERE DID THEY GIVE US THE TOTAL NUMBER OF MOLES :O :O coz I went and had to calculate it manually, undead up getting it wrong.. but my method was the same arghhhhhh DPMO
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    (Original post by ActaNonVerba)
    WHERE DID THEY GIVE US THE TOTAL NUMBER OF MOLES :O :O
    In the second line of the question I believe.
 
 
 
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