Page 5 of 81 FirstFirst ... 345671555 ... LastLast
Results 101 to 125 of 2014
Like Tree191Likes

Thread: HSC 2012-2015 Chemistry Marathon (archive)

  1. #101
    Junior Member
    Join Date
    Mar 2012
    HSC
    2012
    Gender
    Male
    Location
    Sydney
    Posts
    245
    Rep Power
    5

    Re: HSC 2012 Chemistry Marathon

    This is from Independent 09 Trial Exam

    Multiple Choice Q3:

    3. The molar heat of combustion of ethanol is 1367kJ/mol
    What mass of ethanol is required to heat 1.0 moles of water by 10 degrees.

    a - 136.7g
    b - 46.0g
    c - 25.3g
    d - 0.025g

  2. #102
    New Member
    Join Date
    Oct 2011
    HSC
    2013
    Gender
    Male
    Posts
    24
    Rep Power
    5

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    Question:

    A. Amphiprotic species are those that can act as proton donors as well as proton acceptors. For example when HCl is added, HCO3- + H+ -> H2CO3. In this case the bicarbonate ion has accepted a proton thus act as a proton acceptor. However when titrated against NaOH, HCO3- + OH- -> H2O(l) + CO32-, where the bicaronate ion act as a proton donor, donating a hydrogen ion to the hydroxide. HCO3-, able to donate as well as accept hydrogen ions is thus amphiprotic.
    B. 8




    QUESTIOn
    Explain the process of filtration by microscopic membrane filters with reference to their design and composition.
    Last edited by EazyEEE; 23 Apr 2012 at 9:34 PM.

  3. #103
    Junior Member
    Join Date
    May 2012
    HSC
    2012
    Gender
    Male
    Posts
    102
    Rep Power
    4

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by EazyEEE View Post
    A. Amphiprotic species are those that can act as proton donors as well as proton acceptors. For example when HCl is added, HCO3- + H+ -> H2CO3. In this case the bicarbonate ion has accepted a proton thus act as a proton acceptor. However when titrated against NaOH, HCO3- + OH- -> H2O(l) + CO32-, where the bicaronate ion act as a proton donor, donating a hydrogen ion to the hydroxide. HCO3-, able to donate as well as accept hydrogen ions is thus amphiprotic.
    B. 8




    QUESTIOn
    Explain the process of filtration by microscopic membrane filters with reference to their design and composition.
    Microscopic membrane filters have microscopic pores and the use of appropriate sized filters can avoid the need to chemically treat the water. The filters can be classified as microfiltration, ultrafiltration, nanofiltration or reverse osmosis membranes depending on the size of the pore.
    The membrane is made from synthetic polymers dissolved in a mixture of solvents.

    Semi-permeable membranes used in reverse osmosis are either made of cellulose acetate or a layer of polyamide attached to another polymer. Under pressure these polymers allow the passage of water molecules but not that of most atoms, ions or other molecules.

    Water is made to flow across the membrane not through it. This reduces the blockage of the pores and contaminants are carried away as waste. The membrane is housed in a pressure vessel and is either made as a wound spiral or hollow fibres.

    Microfiltration removes protozoans, bacteria, colloids, some colouration and some viruses. The size of the pore determines which sized particle or organism may pass through the membrane. The finer the pore size the smaller the particles trapped and the more expensive the membrane.

    Question- explain, with an example, how oxidation states allow chemists to decide whether or not a reaction involves electron transfer. (assume 3 marks for this quest)
    Last edited by VJ30; 26 May 2012 at 5:01 PM.

  4. #104
    Junior Member
    Join Date
    May 2012
    HSC
    2012
    Gender
    Male
    Posts
    102
    Rep Power
    4

    Re: HSC 2012 Chemistry Marathon

    bump
    explain, with an example, how oxidation states allow chemists to decide whether or not a reaction involves electron transfer. (assume 3 marks for this quest)

  5. #105
    Executive Member nightweaver066's Avatar
    Join Date
    Jul 2010
    HSC
    2012
    Gender
    Male
    Posts
    1,590
    Rep Power
    7

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by VJ30 View Post
    bump
    explain, with an example, how oxidation states allow chemists to decide whether or not a reaction involves electron transfer. (assume 3 marks for this quest)
    Your response to that membrane filter was great.

    Of course, in an exam, diagram!

    If oxidation state increases, oxidation has occured and an electron has been released.

    If oxidation state decreases, reduction has occured and an electron has been captured.

    In redox reactions, if oxidation occurs, a reduction reaction must occur.

    If the oxidation state of one reactant increases, and decreases for another reactant in the same reaction, this means an electron has been released by one of the reactants the same electron was captured by the other revealing that the reaction involves an electron transfer.

    Therefore, by monitoring the oxidation states of reactants in a reaction, if one increases and another decreases of the same magnitude, a reaction involving an electron transfer has occured.




    Now,

    Assess the effectiveness of monitoring and managing CFC & halon production & usage. (5)
    Last edited by nightweaver066; 28 Jun 2012 at 12:40 AM.

  6. #106
    Cadet
    Join Date
    Jun 2012
    HSC
    2012
    Gender
    Male
    Posts
    82
    Rep Power
    4

    Re: HSC 2012 Chemistry Marathon

    In this option you studies one natural product that was not a fossil fuel. Describe the issues associated with shrinking world supplies of this natural product, and evaluate progress being made to solve the problems identified.

    Marks : 10

    Criteria
    Identifies an appropriate natural product
    Provides a judgement
    Provides characteristics and features of at least TWO issues associated with shrinking world supplies of the natural product
    Provides characteristics and features of progress being made to find replacement materials
    Provides a response that demonstrate coherence and logical progression and includes correct use of scientific principles and idea
    HSC 2012
    Std English l Biology l Chemistry l Mathematics l Mathematics Ext 1 l Italian Beginners

    ATAR : 95.90
    HBHS '12

    UTS 2016

  7. #107
    Cadet
    Join Date
    Jun 2012
    HSC
    2012
    Gender
    Male
    Posts
    82
    Rep Power
    4

    Re: HSC 2012 Chemistry Marathon

    Industrial Chemistry Question ^
    HSC 2012
    Std English l Biology l Chemistry l Mathematics l Mathematics Ext 1 l Italian Beginners

    ATAR : 95.90
    HBHS '12

    UTS 2016

  8. #108
    Retired Nov '14 someth1ng's Avatar
    Join Date
    Sep 2010
    HSC
    2012
    Uni Grad
    2016
    Gender
    Male
    Location
    Sydney, Australia
    Posts
    5,480
    Rep Power
    9

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post

    - Ethene is usually produced from the cracking of large hydrocarbons.
    - The cracking of a large alkane always produces a small alkene, usually ethene and occasionally propene, and a large alkane.
    - The cracking process involves heating the hydrocarbons to 500C with a zeolite catalyst in the absence of oxygen to prevent combustion.
    --> Example: C8H18 --> C2H4 + C6H14
    - The zeolite catalyst adsorb alkanes, weakening their bonds is required because the activation energy of cracking without a catalyst is very high, requiring immensely high temperatures making it uneconomical.
    - Ethene can then be separated from the hydrocarbons by cooling the gas where 5-carbon alkyl chains will condense into liquids.
    - Ethene can be separated from small the other smaller hydrocarbons such as propene by fractional distillation, if necessary.
    Penrith High School '12

    Bachelor of Science (Advanced) (Chemistry, Environmental Studies) '15
    University of Sydney

    Bachelor of Science (Advanced) (Honours) (Chemistry)
    University of Sydney

  9. #109
    Executive Member nightweaver066's Avatar
    Join Date
    Jul 2010
    HSC
    2012
    Gender
    Male
    Posts
    1,590
    Rep Power
    7

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    - Ethene is usually produced from the cracking of large hydrocarbons.
    - The cracking of a large alkane always produces a small alkene, usually ethene and occasionally propene, and a large alkane.
    - The cracking process involves heating the hydrocarbons to 500C with a zeolite catalyst in the absence of oxygen to prevent combustion.
    --> Example: C8H18 --> C2H4 + C6H14
    - The zeolite catalyst adsorb alkanes, weakening their bonds is required because the activation energy of cracking without a catalyst is very high, requiring immensely high temperatures making it uneconomical.
    - Ethene can then be separated from the hydrocarbons by cooling the gas where 5-carbon alkyl chains will condense into liquids.
    - Ethene can be separated from small the other smaller hydrocarbons such as propene by fractional distillation, if necessary.
    Great response

    Been so long i've forgotten about this thread..


  10. #110
    Retired Nov '14 someth1ng's Avatar
    Join Date
    Sep 2010
    HSC
    2012
    Uni Grad
    2016
    Gender
    Male
    Location
    Sydney, Australia
    Posts
    5,480
    Rep Power
    9

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    Great response

    Been so long i've forgotten about this thread..

    - There are many ways a radioisotope can be produced.
    - Two such methods include neutron bombardment and nuclear fission.
    --> Both of these methods are frequent used as induced nuclear transformations.
    - Neutron bombardment usually involves bombarding a certain nuclei with a neutron but does not necessarily involve the product to undergo fission to produce smaller products, as seen in the case of Technetium-99m.
    [Equation] Mo-98+neutron-->Mo-99
    [Equation] Mo-99-->Tc-99m+electron+gamma
    - Nuclear fission often involves the bombardment of a certain nuclei or particle (including neutrons) causing it to spontaneously undergo fission to produce smaller products, as seen in the case of Strontium-90.
    [Equation] U-235+neutron-->Xe-138+Sr-90+8neutrons+gamma
    - Evidently, although both methods are different, they are both used to produce radioisotopes.

    Fairly plain response but I think it'd get 3/4, not exactly a 4/4 response, in my opinion.

    Assess the impact of atomic absorption spectroscopy (AAS) on our understanding of trace elements. (3 marks)
    Penrith High School '12

    Bachelor of Science (Advanced) (Chemistry, Environmental Studies) '15
    University of Sydney

    Bachelor of Science (Advanced) (Honours) (Chemistry)
    University of Sydney

  11. #111
    Executive Member nightweaver066's Avatar
    Join Date
    Jul 2010
    HSC
    2012
    Gender
    Male
    Posts
    1,590
    Rep Power
    7

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    - There are many ways a radioisotope can be produced.
    - Two such methods include neutron bombardment and nuclear fission.
    --> Both of these methods are frequent used as induced nuclear transformations.
    - Neutron bombardment usually involves bombarding a certain nuclei with a neutron but does not necessarily involve the product to undergo fission to produce smaller products, as seen in the case of Technetium-99m.
    [Equation] Mo-98+neutron-->Mo-99
    [Equation] Mo-99-->Tc-99m+electron+gamma
    - Nuclear fission often involves the bombardment of a certain nuclei or particle (including neutrons) causing it to spontaneously undergo fission to produce smaller products, as seen in the case of Strontium-90.
    [Equation] U-235+neutron-->Xe-138+Sr-90+8neutrons+gamma
    - Evidently, although both methods are different, they are both used to produce radioisotopes.

    Fairly plain response but I think it'd get 3/4, not exactly a 4/4 response, in my opinion.
    I think you should include the technology/machinery involved or comparing something else to get 4/4

    Assess the impact of atomic absorption spectroscopy (AAS) on our understanding of trace elements. (3 marks)
    - AAS is a quantitative analysis technique for determining small concentrations of metals in samples.
    - Using AAS, scientists have been able to monitor and understand the effect of certain concentrations of trace elements such as cobalt and copper in agricultural land for optimum crop growth
    - However, AAS has detection limits in determining concentrations (e.g. detection limit of 1ppb for lead in water samples) and so cannot monitor the effects of such small concentrations
    - Overall, AAS has made a profound impact on our understanding of trace elements as farmers are able to optimise plant growth as [Pb] < 1 ppb does not greatly effect plant growth (made this part up, is it fine? lol)


    Question:
    Last edited by nightweaver066; 19 Sep 2012 at 12:09 AM.

  12. #112
    Retired Nov '14 someth1ng's Avatar
    Join Date
    Sep 2010
    HSC
    2012
    Uni Grad
    2016
    Gender
    Male
    Location
    Sydney, Australia
    Posts
    5,480
    Rep Power
    9

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    I think you should include the technology/machinery involved or comparing something else to get 4/4

    - AAS is a quantitative analysis technique for determining small concentrations of metals in samples.
    - Using AAS, scientists have been able to monitor and understand the effect of certain concentrations of trace elements such as cobalt and copper in agricultural land for optimum crop growth
    - However, AAS has detection limits in determining concentrations (e.g. detection limit of 1ppb for lead in water samples) and so cannot monitor the effects of such small concentrations
    - Overall, AAS has made a profound impact on our understanding of trace elements as farmers are able to optimise plant growth as [Pb] < 1 ppb does not greatly effect plant growth (made this part up, is it fine? lol)
    Yeah, I know...I felt that the marking scheme would expect at least two valid comparisons (2 marks, 1 mark for each comparison), identifying two methods (1 mark), identifying two examples (1 mark).

    1. Another comparison could be:
    Neutron bombardment usually does not require acceleration as neutrons hold no electrical charge, as it is not repelled by the positive nuclei by electrostatic repulsion, it won't need to be forces into the nucleus.
    Nuclear fission can often require bombardment of a positively charged nuclei, this means that it must be accelerated to very high speeds to overcome electrostatic repulsion and allowing a new nucleus to be formed which could spontaneously decay into smaller molecules.

    2. How? Give an example such as in South Australia, what appeared to be land very suitable for agriculture did not thrive and it was found that cobalt deficiency did not allow grass to grow for grazing.

    3. Never make information up, you get 0 marks for it. If you said "extremely miniscule amounts of many heavy metals (eg lead) such that it is undetectable by AAS usually does not have a significant adverse effect on plant growth", you could have gotten a good mark for it and being general but "academic" makes your work more favourable.
    Penrith High School '12

    Bachelor of Science (Advanced) (Chemistry, Environmental Studies) '15
    University of Sydney

    Bachelor of Science (Advanced) (Honours) (Chemistry)
    University of Sydney

  13. #113
    Executive Member nightweaver066's Avatar
    Join Date
    Jul 2010
    HSC
    2012
    Gender
    Male
    Posts
    1,590
    Rep Power
    7

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    Yeah, I know...I felt that the marking scheme would expect at least two valid comparisons (2 marks, 1 mark for each comparison), identifying two methods (1 mark), identifying two examples (1 mark).

    1. Another comparison could be:
    Neutron bombardment usually does not require acceleration as neutrons hold no electrical charge, as it is not repelled by the positive nuclei by electrostatic repulsion, it won't need to be forces into the nucleus.
    Nuclear fission can often require bombardment of a positively charged nuclei, this means that it must be accelerated to very high speeds to overcome electrostatic repulsion and allowing a new nucleus to be formed which could spontaneously decay into smaller molecules.

    2. How? Give an example such as in South Australia, what appeared to be land very suitable for agriculture did not thrive and it was found that cobalt deficiency did not allow grass to grow for grazing.

    3. Never make information up, you get 0 marks for it. If you said "extremely miniscule amounts of many heavy metals (eg lead) such that it is undetectable by AAS usually does not have a significant adverse effect on plant growth", you could have gotten a good mark for it and being general but "academic" makes your work more favourable.
    Didn't think i needed to be very specific with the example.

    Thanks for the feedback

  14. #114
    Retired Nov '14 someth1ng's Avatar
    Join Date
    Sep 2010
    HSC
    2012
    Uni Grad
    2016
    Gender
    Male
    Location
    Sydney, Australia
    Posts
    5,480
    Rep Power
    9

    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    Didn't think i needed to be very specific with the example.

    Thanks for the feedback
    I just thought it wasn't detailed enough, how have they understood it? Those sort of questions, in a way, undermine your answer to some extent since it doesn't fully address all aspects of the question. It's probably better to do too much than too little.

    That's my thoughts, at least. But otherwise, you're doing well.
    Penrith High School '12

    Bachelor of Science (Advanced) (Chemistry, Environmental Studies) '15
    University of Sydney

    Bachelor of Science (Advanced) (Honours) (Chemistry)
    University of Sydney

  15. #115
    Executive Member bleakarcher's Avatar
    Join Date
    Jul 2011
    HSC
    2013
    Gender
    Male
    Posts
    1,512
    Rep Power
    6

    HSC Chemistry Marathon

    The HSC Chemistry Marathon is an open chain of questions between students. It works by answering a question then posting another question and allowing the cycle to repeat itself.

    Rules:
    - After answering a question, always provide a new one - this is what keeps the thread alive.
    - Allocate a number of marks for any question that you post.
    - Do not cheat, if you cannot answer a question, do not search how to answer the question but rather, allow other students to answer the question.
    - No copyrighted questions (eg CSSA and Independent) should be posted.

    Tips:
    - It may help to write your answers on paper before typing them on this thread as it will mirror your exam.
    - You may post more than one question.
    - When possible, after questions have been answered, you can peer mark using the marking scheme.
    Last edited by someth1ng; 19 Feb 2013 at 11:13 PM.
    Physics is to mathematics like sex is to masturbation.” —Richard Feynman

  16. #116
    This too shall pass Sy123's Avatar
    Join Date
    Nov 2011
    HSC
    2013
    Gender
    Male
    Posts
    3,725
    Rep Power
    7

    re: HSC Chemistry Marathon Archive





    There is a one to one ratio between HCl and H+

    Hence





    We get 0.105 from the Volume of the soln which is 105 ml
    We now have conecntration of Hydrogen ions, so we take -log of it



    I hope I'm right lol

    =======================

    How is it possible to have NEUTRAL water at ph6?


    (just brief and straight to the point)
    Many a man and dynasty have we seen,
    That all quickly perished and expired;
    Many a mountaintop was surmounted,
    By men, who perished, yet the mountains remain

    - Fakhr al-Din al-Razi

  17. #117
    Executive Member bleakarcher's Avatar
    Join Date
    Jul 2011
    HSC
    2013
    Gender
    Male
    Posts
    1,512
    Rep Power
    6

    re: HSC Chemistry Marathon Archive

    Correct.

    Isn't neutral water defined with pH 7?
    Physics is to mathematics like sex is to masturbation.” —Richard Feynman

  18. #118
    This too shall pass Sy123's Avatar
    Join Date
    Nov 2011
    HSC
    2013
    Gender
    Male
    Posts
    3,725
    Rep Power
    7

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by bleakarcher View Post
    Correct.

    Isn't neutral water defined with pH 7?
    I would tell you why this is not the case, but it would give the answer away haha.

    EDIT: I didn't want to kill the thread this early, here is another question in the mean time while people think about it

    Upon analysis of mass of a hydrocarbon was found to contain 82.6% Carbon and 17.4% Hydrogen. Calculate its empirical formula
    Last edited by Sy123; 29 Dec 2012 at 10:11 PM.
    Many a man and dynasty have we seen,
    That all quickly perished and expired;
    Many a mountaintop was surmounted,
    By men, who perished, yet the mountains remain

    - Fakhr al-Din al-Razi

  19. #119
    #MedLyf Riproot's Avatar
    Join Date
    Nov 2009
    HSC
    2011
    Uni Grad
    2017
    Gender
    Male
    Posts
    8,261
    Rep Power
    11

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Sy123 View Post
    Upon analysis a hydrocarbon was found to contain 82.6% Carbon and 17.4% Hydrogen. Calculate its empirical formula
    What sort of analysis?

    Without knowing the type of analysis you don't know whether it is mol% or mass%

  20. #120
    This too shall pass Sy123's Avatar
    Join Date
    Nov 2011
    HSC
    2013
    Gender
    Male
    Posts
    3,725
    Rep Power
    7

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Riproot View Post
    What sort of analysis?

    Without knowing the type of analysis you don't know whether it is mol% or mass%
    Fixed. But as far as I know it is impossible for there to be those numerical percentages and it meaning mol%, the Carbon - Hydrogen ratio is too high for it to be mol.
    Many a man and dynasty have we seen,
    That all quickly perished and expired;
    Many a mountaintop was surmounted,
    By men, who perished, yet the mountains remain

    - Fakhr al-Din al-Razi

  21. #121
    Executive Member theind1996's Avatar
    Join Date
    Sep 2011
    HSC
    N/A
    Gender
    Undisclosed
    Location
    Menai
    Posts
    1,255
    Rep Power
    5

    re: HSC Chemistry Marathon Archive

    Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?
    Quote Originally Posted by Kiraken View Post
    Lol fak my uncle just told me I have very distant and slight Greek and arab ancestry mixed in with my paki/Indian heritage

    Dammit why am I still such a nigga

  22. #122
    #MedLyf Riproot's Avatar
    Join Date
    Nov 2009
    HSC
    2011
    Uni Grad
    2017
    Gender
    Male
    Posts
    8,261
    Rep Power
    11

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Sy123 View Post
    Fixed. But as far as I know it is impossible for there to be those numerical percentages and it meaning mol%, the Carbon - Hydrogen ratio is too high for it to be mol.
    But still! It's the principle of the thing.

    (It's gravimetric analysis or something, right?)

  23. #123
    #MedLyf Riproot's Avatar
    Join Date
    Nov 2009
    HSC
    2011
    Uni Grad
    2017
    Gender
    Male
    Posts
    8,261
    Rep Power
    11

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by theind1996 View Post
    Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?
    The pH 6 one would be one of the tricky ones but the percentage one is fine. I think we did more of that stuff in year 11 though iirc.

  24. #124
    This too shall pass Sy123's Avatar
    Join Date
    Nov 2011
    HSC
    2013
    Gender
    Male
    Posts
    3,725
    Rep Power
    7

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by theind1996 View Post
    Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?
    They are both within syllabus standards not sure what you mean by HSC level.
    Many a man and dynasty have we seen,
    That all quickly perished and expired;
    Many a mountaintop was surmounted,
    By men, who perished, yet the mountains remain

    - Fakhr al-Din al-Razi

  25. #125
    Executive Member theind1996's Avatar
    Join Date
    Sep 2011
    HSC
    N/A
    Gender
    Undisclosed
    Location
    Menai
    Posts
    1,255
    Rep Power
    5

    re: HSC Chemistry Marathon Archive

    Quote Originally Posted by Riproot View Post
    The pH 6 one would be one of the tricky ones but the percentage one is fine. I think we did more of that stuff in year 11 though iirc.
    Oh yeah shit.

    The empirical formula is from moles shit in Yr 11.

    Post some more Production questions guys? I think most people haven't done Acidic in great depth.
    Quote Originally Posted by Kiraken View Post
    Lol fak my uncle just told me I have very distant and slight Greek and arab ancestry mixed in with my paki/Indian heritage

    Dammit why am I still such a nigga

Page 5 of 81 FirstFirst ... 345671555 ... LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •