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OCR Chemistry F322~ 4th June 2013~ AS Chemistry Watch

  • View Poll Results: How did you find the exam
    Hard A= 72
    42
    15.22%
    It was okay A= 76
    99
    35.87%
    Easy A= 79
    75
    27.17%
    Very Easy A=82
    60
    21.74%

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    (Original post by Josh989)
    Hi just wondering if someone could help me, by looking through my textbox it says; enthalpy change of formation is 'sum of enthalpy of PRODUCTS - sum of enthalpy of REACTANTS'
    However I have come across this question;
    The standard enthalpy change of formation of hexane can be determined indirectly.
    Calculate the standard enthalpy change of formation of hexane using the standard
    enthalpy changes of combustion below.

    substance  Hc / kJ mol–1
    C –394
    H2 –286
    C6 H14 –4163
    Equation; 6C + 7H2 -------> C6H14
    And the answer is -203...
    However I got +203 when I did it with the original equation??? Is it because all the reactants/product are minus so the answer follows? Or because the forward reaction is exothermic so the H change follows?? Little confused
    If you could help in anyway I would be very greatful!!! Exam tomorrow :O!!!
    the equation is saying the products - reactants using combustion values
    so if youve drawn a hess's law cycle, the arrows should be going down
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    (Original post by Kits)
    I got a medium B in Jan
    Got like 39 on coursework

    What do I need to do in this exam for an A? Will scraping an A be enough or do I have to smash it
    240 ums for A

    Med b assuming that's 46 raw marks so 68 ums

    39/40 is 59 ums

    So you need about 113/150
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    (Original post by Josh989)
    Hi just wondering if someone could help me, by looking through my textbox it says; enthalpy change of formation is 'sum of enthalpy of PRODUCTS - sum of enthalpy of REACTANTS'
    However I have come across this question;
    The standard enthalpy change of formation of hexane can be determined indirectly.
    Calculate the standard enthalpy change of formation of hexane using the standard
    enthalpy changes of combustion below.

    substance Hc / kJ mol–1
    C –394
    H2 –286
    C6 H14 –4163
    Equation; 6C + 7H2 -------> C6H14
    And the answer is -203...
    However I got +203 when I did it with the original equation??? Is it because all the reactants/product are minus so the answer follows? Or because the forward reaction is exothermic so the H change follows?? Little confused
    If you could help in anyway I would be very greatful!!! Exam tomorrow :O!!!
    That's a hess's law question, so either draw the triangle with the arrows pointing down or remember deltaHc is reactants-products. The equation you stated is only for bond enthalpies.
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    (Original post by needtosucceed=))
    yea im resitting unit 2 are u?
    yes and resitting from yr 11 believe it or not


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    (Original post by Jimmy20002012)
    Say we get a question on how scientists are trying to reduce greenhouse gas emissions Would you say this:

    - Carbon Capture and Storage is being developed
    - Examples of CCS include carbon being stored deep in the oceans, geological formations, reacting with metal oxides.
    - Educating society of how to reduce these greenhouse emissions
    - use hybrid cars as this is a much efficient way of travel and releases less greenhouse gases.
    - Government are being informed and Kyoto and Montreal protocol are in place which reduce countries who signed up release less greenhouse emission
    - uses of CO2 are being developed such as a blowing agent



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    yep those are fine
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    (Original post by krishkmistry)
    yes and resitting from yr 11 believe it or not


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    you did AS business in year 11?
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    (Original post by Jimmy20002012)
    Say we get a question on how scientists are trying to reduce greenhouse gas emissions Would you say this:

    - Carbon Capture and Storage is being developed
    - Examples of CCS include carbon being stored deep in the oceans, geological formations, reacting with metal oxides.
    - Educating society of how to reduce these greenhouse emissions
    - use hybrid cars as this is a much efficient way of travel and releases less greenhouse gases.
    - Government are being informed and Kyoto and Montreal protocol are in place which reduce countries who signed up release less greenhouse emission
    - uses of CO2 are being developed such as a blowing agent



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    Sorry to butt in out of the blue,were the PowerPoint things any good ?


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    (Original post by needtosucceed=))
    - moles/molar mass.
    - q=deltaH x n (when calculating n multiply your previous answer by 7 as theres 7 moles of co2 in the equation u wrote for the other question)
    - volume = n x 24

    use those equations, if you're still stuck lemme know.
    is 'i' 20mol?
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    (Original post by needtosucceed=))
    what was your ums for unit 1?
    Literally no idea lol..
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    (Original post by Jonma)
    Do you have to learn all of the fractions and their uses in fractional distillation, or just the process? I noticed that a fact recall for it has never come up.
    nope.
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    (Original post by Blashnet)
    is 'i' 20mol?
    correct
    • Thread Starter
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    (Original post by krishkmistry)
    Sorry to butt in out of the blue,were the PowerPoint things any good ?


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    They were really good, thanks. Basically memorised the mark schemes haha


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    (Original post by Kits)
    Literally no idea lol..
    lol fair enough. you should be fine if you scrape an A, ur practicals are high
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    (Original post by needtosucceed=))
    correct
    yay thanks :innocent:
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    (Original post by Jimmy20002012)
    They were really good, thanks. Basically memorised the mark schemes haha


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    great,so have I - lets hope it pays off tomorrow! Good luck


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    Hey!

    I got 49/60 unit one (72 ums) and 37/40 in pracs (dont know what UMS)

    Anyone got any idea of what raw/ums mark i'd need for an A?
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    Like if you learn more on student room than in lessons!!! Lool
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    Link to January 2013 paper and mark scheme anyone ? Thank you
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    (Original post by Blashnet)
    Hey!

    I got 49/60 unit one (72 ums) and 37/40 in pracs (dont know what UMS)

    Anyone got any idea of what raw/ums mark i'd need for an A?
    75-77 would be enough
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    (Original post by ssflcb)
    Link to January 2013 paper and mark scheme anyone ? Thank you
    its in the first post of this thread
 
 
 
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