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Thread: HSC 2012-2015 Chemistry Marathon (archive)

  1. #2001
    Executive Member Ekman's Avatar
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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by rand_althor View Post
    Not sure if this question has popped up before:

    Compare the chemical processes involved in the production of polyethylene and a named biopolymer (not cellulose) and evaluate the effect on society and the environment of both types of polymers. (7 marks)
    This exact question popped up in my trials. Where did you get it from?
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    re: HSC Chemistry Marathon Archive

    Also can someone please re-iterate the rules about sig figs? If the data gives 0.001molL-1, does that mean it has 1 sig fig?
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  3. #2003
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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Ekman View Post
    This exact question popped up in my trials. Where did you get it from?
    It was in my trials too.

    Quote Originally Posted by Mr_Kap View Post
    I really dont know how to get 7 marks. Like i can only find differences between them not similarities.

    Can you put in dot points what you need to mention for full marks.
    The marking criteria (6-7 marks):
    - Describes ONE or TWO similarities between the chemical processes involved in the production of polyethylene and the named biopolymer
    - Describes at least TWO differences between the chemical processes involved in the production of polyethylene and the named biopolymer
    - Describes an impact of the use of each polymer on society
    - Describes an impact of the use of each polymer on the environment
    - Make a clear judgement about the use of each type of polymer on society and the environment
    - Answer is cohesive, comprehensive and demonstrates a thorough understanding of the science of the chemical processes involved

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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Ekman View Post
    Also can someone please re-iterate the rules about sig figs? If the data gives 0.001molL-1, does that mean it has 1 sig fig?
    shit. i forgot sig figures rules.Someone help!!!

    and Is 1.00 mol/L 1 sig fig or 3 sig fig???
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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Ekman View Post
    Also can someone please re-iterate the rules about sig figs? If the data gives 0.001molL-1, does that mean it has 1 sig fig?
    I brought it up with Fizzy at one point in time

    You round your answer off to the lowest amount of significant figures in the question (e.g. There's 90 kg, 555 N so you choose the number of sig figs in the 90 kg) BUT that value actually has to be used in the actual calculation - My school got sneaky with the half-yearlies where they included some BS value that wasn't included in the calculation and heaps of people rounded it off to the amount of significant figures it had (since it had the lowest)
    Last edited by Crisium; 22 Oct 2015 at 10:06 PM.
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    re: HSC Chemistry Marathon Archive

    what about 0.001 mol/L. How many sig figures is that..


    and what about 1.00 mol/L how many sig figures is that
    Advanced Science & Computer Science - UNSW

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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Mr_Kap View Post
    what about 0.001 mol/L. How many sig figures is that..


    and what about 1.00 mol/L how many sig figures is that
    LOL

    Oh you're talking about the general sig fig rules?

    You only begin counting sig figs after the zero's so it's 1 sig fig in the first thing

    For the second thing the .00 tells us something interesting after the 1 so it's 3 sig figs
    Quote Originally Posted by enigma_1 View Post
    "HSC is a once in a lifetime experience"
    Quote Originally Posted by hawkrider View Post
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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Ekman View Post
    Also can someone please re-iterate the rules about sig figs? If the data gives 0.001molL-1, does that mean it has 1 sig fig?
    Yeah that's 1 sig. fig.

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    re: HSC Chemistry Marathon Archive

    http://www.purplemath.com/modules/rounding2.htm

    Have a quick skim over the examples

    Good luck for chem everyone

    I'm gonna head off and get some pracs memorised
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    Quote Originally Posted by enigma_1 View Post
    "HSC is a once in a lifetime experience"
    Quote Originally Posted by hawkrider View Post
    Quality is important, but quantity is quality in itself.

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    re: HSC Chemistry Marathon Archive





    Last edited by InteGrand; 22 Oct 2015 at 10:22 PM.
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    re: HSC Chemistry Marathon Archive

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  12. #2012
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    re: HSC Chemistry Marathon Archive


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    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Loudvicuna View Post
    Le Chatelier's Principle (LCP) states that a disturbance experienced by an equilibrium will cause the equilibrium to shift, in order to minimise the disturbance. In step 1, the mole ratio of gases of reactants to products is 9:10 and thus, to maximise the yield, a low pressure is used. With a lower pressure, the equilibrium will favour the products as it has more gaseous moles and shift to produce more nitric oxide used in step 2. Since it is also the most highly exothermic reaction in the process, a relatively higher temperature can be used (to maximise reaction rate) as the equilibrium will not shift backwards too substantially. In step 2, the use of a high pressure causes the equilibrium to shift forward, to the less gaseous moles and producing more nitrogen dioxide. The use of lower pressure (lower than step 1 but still moderate) is used to balance out the reaction rate and the yield produced (since equilbrium will shift forward). In step 3, the use of high pressure is also used, as the mole ratio of raectants to products is 3 to 1. This will allow the equilibrium to shift forward to produce more of the required nitric acid. The use of a moderate temperature is also used to balance out reaction rate and yield.
    The optimising of step 1 helps optimise step 2 due to the increased concentration of nitric oxide and also helps optimise step 3 due to increase in nitrogen dioxide.
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  14. #2014
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    Re: HSC Chemistry Marathon Archive

    This thread is an archive. Please post in the thread linked below for anything regarding a question in this thread:

    http://community.boredofstudies.org/...on-2016-a.html

    Make sure to quote what you are inquiring about!

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