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Thread: HSC 2012-2015 Chemistry Marathon (archive)

  1. #51
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by viraj30 View Post
    what is the temperature and pressure in which high density polyethylene is made? (confused bcos in excel it says 'just above 300 celsius' whereas in KISS booklet it says at about 60 celsius..which ones correct..can it b a typo
    60C is correct AFAIK.
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by kingkong123 View Post
    LDPE is conducted in an environment with pressure equivalent to approximately 3000 atmospheres, and with extremely high temperatures. The high pressure atmosphere leads to haphazard branching in the propagation process, leading to the low density. HDPE on the other hand is conducted using the Ziggler-Natta process. Pressure equivalent to only a few atmospheres is required with low temperatures, due to the catalyst present. This low pressure results in a tightly packed, high density polymer.

    Right/Wrong?
    Correct, it's "Ziegler-Natta" by the way. Having poor spelling gives the impression that you don't know which you clearly do.
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by deswa1 View Post
    Evaluate the impact of industrial sources of sulfur dioxide and nitrogen oxides on the environment, making use of appropriate chemical equations. (7)
    These are what I wrote a couple of days ago:
    • Oxides of sulphur and nitrogen are highly acidic and toxic.
    • These oxides cause environmental issues such as acid rain and the release of toxic fumes and the levels of these oxides have been rising since the industrial revolution.
    • Sulphur oxides: Sulphur Dioxide (SO2) and Sulphur Trioxide (SO3)
    • Nitrogen Oxides: General formula of NXOY
    • Sulphur oxides react with water to form corrosive acids:
    H2O(l) + SO2(g) --> H2SO3 (aq) [Sulphurous Acid]
    H2O(l) + SO3(g) --> H2SO4 (aq) [Sulphuric Acid]
    • Sulphuric acid is a strong acid with highly corrosive properties and can quickly damage and even destroy flora and fauna in the environment.
    • Sulphuric acid can also corrode important monuments and stone buildings and statues, especially if they readily react with acids such as limestone.
    • Many Nitrogen Oxides are also highly corrosive, especially Nitric Acid have a potential to pose extreme harm to humans due to its corrosive nature.
    • Some Nitrogen oxides form acids in solution and some are toxic gases:
    H2O(l) + NO2 (g) --> HNO3(aq)+HNO2(aq) [Nitric Acid and Nitrous Acid]
    Dinitrogen Tetroxide: N2O4(g) is a highly toxic gas as it is a powerful oxidiser and inhaling this gas in significant quantities can be fatal.

    I think this is a pretty solid answer.

    Next question:
    Clearly indicate the similarities and differences between the model of acids described by Humphrey Davy and the model developed by Bronsted and Lowry.
    Last edited by someth1ng; 25 Feb 2012 at 3:21 PM.
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    These are what I wrote a couple of days ago:
    • Oxides of sulphur and nitrogen are highly acidic and toxic.
    • These oxides cause environmental issues such as acid rain and the release of toxic fumes and the levels of these oxides have been rising since the industrial revolution.
    • Sulphur oxides: Sulphur Dioxide (SO2) and Sulphur Trioxide (SO3)
    • Nitrogen Oxides: General formula of NXOY
    • Sulphur oxides react with water to form corrosive acids:
    H2O(l) + SO2(g) --> H2SO3 (aq) [Sulphurous Acid]
    H2O(l) + SO3(g) --> H2SO4 (aq) [Sulphuric Acid]
    • Sulphuric acid is a strong acid with highly corrosive properties and can quickly damage and even destroy flora and fauna in the environment.
    • Sulphuric acid can also corrode important monuments and stone buildings and statues, especially if they readily react with acids such as limestone.
    • Many Nitrogen Oxides are also highly corrosive, especially Nitric Acid have a potential to pose extreme harm to humans due to its corrosive nature.
    • Some Nitrogen oxides form acids in solution and some are toxic gases:
    H2O(l) + NO2 (g) --> HNO3(aq)+HNO2(aq) [Nitric Acid and Nitrous Acid]
    Dinitrogen Tetroxide: N2O4(g) is a highly toxic gas as it is a powerful oxidiser and inhaling this gas in significant quantities can be fatal.

    I think this is a pretty solid answer.

    Next question:
    You should talk about acid rain.

    You should include a chemical equation in the chemical corrosion of limestone buildings.

    Your chemical equation for the formation for nitric and nitrous acid is not balanced, it is 2H2O(l).

    How can sulphuric acid destroy fauna? Fauna = animals. Perhaps say something about increasing acidity of inland water bodies such that the pH decreases.
    Aquatic life cannot sustain themselves at pH < 5, and will eventually die if the pH decreases to that level due to acid rain.

    Nitrogen oxides are not harmful to humans due to their corrosive nature, but due to their ability to ionise in to acids if the gases are inhaled. Same applies to sulphur oxides.
    Last edited by nightweaver066; 25 Feb 2012 at 8:11 PM.

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    Identify the standard conditions required to produce a table of reduction potentials based on galvanic cells constructed using a hydrogen electrode.
    An electrochemical cell is produced using two half cells. One cell consists of a solution of Fe2+ and Fe3+ with an inert platinum electrode, the other cell consists of a copper electrode in a solution of Cu2+. Write equations for each half cell and calculate the expected standard cell potential.
    hydrogen half cell*

    Quote Originally Posted by someth1ng View Post
    I will just dot point this:

    - Ethanol is the most used solvent because it has the ability to be a solvent for both polar and non-polar substances.
    - The polar hydroxide functional group gives ethanol the ability to be miscible in polar substances.
    - The non-polar alkyl part allows ethanol to be miscible in non-polar substances.
    - Essentially, having the ability to be miscible in both polar and non-polar substances gives ethanol more effectiveness as a solvent.
    Quote Originally Posted by nightweaver066 View Post
    Good answer. In a test, hopefully you'll draw a nice structural formula of ethanol showing both the hydroxide functional group and the alkyl chain.

    Post a new questions please!
    hydroxy or hydroxyl*

    Quote Originally Posted by kingkong123 View Post
    LDPE is conducted in an environment with pressure equivalent to approximately 3000 atmospheres, and with extremely high temperatures. The high pressure atmosphere leads to haphazard branching in the propagation process, leading to the low density. HDPE on the other hand is conducted using the Ziggler-Natta process. Pressure equivalent to only a few atmospheres is required with low temperatures, due to the catalyst present. This low pressure results in a tightly packed, high density polymer.

    Right/Wrong?
    Quote Originally Posted by someth1ng View Post
    Correct, it's "Ziegler-Natta" by the way. Having poor spelling gives the impression that you don't know which you clearly do.
    Having wrong info is even more serious a problem.
    Low pressure doesn't account for the high density of the final product. It's the catalysis itself.

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    You should talk about acid rain.

    You should include a chemical equation in the chemical corrosion of limestone buildings.

    Your chemical equation for the formation for nitric and nitrous acid is not balanced, it is 2H2O(l).

    How can sulphuric acid destroy fauna? Fauna = animals. Perhaps say something about increasing acidity of inland water bodies such that the pH decreases.
    Aquatic life cannot sustain themselves at pH < 5, and will eventually die if the pH decreases to that level due to acid rain.

    Nitrogen oxides are not harmful to humans due to their corrosive nature, but due to their ability to ionise in to acids if the gases are inhaled. Same applies to sulphur oxides.

    • Oxides of sulfur and nitrogen are highly acidic and toxic.
    • These oxides cause environmental issues such as acid rain and the release of toxic fumes and the levels of these oxides have been rising since the industrial revolution.
    • Sulfuric acid is a strong acid with highly corrosive properties and can quickly damage and even destroy flora and fauna by decreasing the pH of inland water bodies in the environment making the water unsustainable for aquatic life.
    • Sulfur oxides: Sulfur Dioxide (SO2) and Sulfur Trioxide (SO3)
    • Nitrogen oxides: General formula of NXOY
    • Sulfur oxides react with water to form corrosive acids:

    H2O(l) + SO2(g) H2SO3 (aq) [Sulfurous Acid]
    H2O(l) + SO3(g) H2SO4 (aq) [Sulfuric Acid]

    • Sulfuric acid can also corrode important monuments and stone buildings and statues, especially if they readily react with acids such as limestone.
    • H2SO4(aq) + CaCO3 à H2O(l) + CO2(g) + CaSO4(aq)
    • Many nitrogen oxides are also highly corrosive due to their potential to ionise into acids such as nitric acid when inhaled.
    • Some nitrogen oxides form acids in solution and some are toxic gases:

    H2O(l) + 2NO2 (g) HNO3(aq)+HNO2(aq) [Nitric Acid and Nitrous Acid]

    • Dinitrogen Tetroxide: N2O4(g) is a highly toxic gas as it is a powerful oxidiser and inhaling this gas in significant quantities can be fatal.

    There, it's now balanced and I think a lot of your points are now covered.
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by study-freak View Post
    Having wrong info is even more serious a problem.
    Low pressure doesn't account for the high density of the final product. It's the catalysis itself.
    The Ziegler-Natta catalyst allows surface polymerisation to occur which results in a tightly packed polymer, but the low pressure is definitely a contributing factor as well. If you look at LDPE, the extremely high pressure results in the radicals backbiting and joining haphazardly, resulting in the low density - by the same token, in HDPE, despite the presence of the catalyst, the low pressure allows for a more controlled propagation process where the monomers can join closely together.

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by kingkong123 View Post
    The Ziegler-Natta catalyst allows surface polymerisation to occur which results in a tightly packed polymer, but the low pressure is definitely a contributing factor as well. If you look at LDPE, the extremely high pressure results in the radicals backbiting and joining haphazardly, resulting in the low density - by the same token, in HDPE, despite the presence of the catalyst, the low pressure allows for a more controlled propagation process where the monomers can join closely together.
    The linearity of the final product when the Ziegler-Natta catalyst is used is a result of its reaction mechanism (enabled by the catalyst), rather than pressure or temperature.
    Back-biting is characteristic of LDPE radical polymerisation reactions, but this reaction is not that of free radicals.

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    Re: HSC 2012 Chemistry Marathon

    since there are no questions in last posts ill post an easy one!- how much it costs to raise 32 litres of water by 20 degrees if it costs 15cents/kwh...??

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by viraj30 View Post
    since there are no questions in last posts ill post an easy one!- how much it costs to raise 32 litres of water by 20 degrees if it costs 15cents/kwh...??
    This is the weirdest question (for Chemistry) that I've seen to date - like, it's not really HSC but LOL
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    This is the weirdest question (for Chemistry) that I've seen to date - like, it's not really HSC but LOL
    Reminds me of physics; Haven't seen kWh for a while now.. haha

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    This is the weirdest question (for Chemistry) that I've seen to date - like, it's not really HSC but LOL
    why is it weird?? does it need more information??? if not then plz gimme an answer im curious

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by viraj30 View Post
    why is it weird?? does it need more information??? if not then plz gimme an answer im curious
    It's fine, it's just not apart of the HSC syllabus or anything like it.
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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by someth1ng View Post
    It's fine, it's just not apart of the HSC syllabus or anything like it.
    then plz i really need an answer! ohk ill show u my method and yous can tell me if im correct or not!

    Energy required= mass x c x delta t
    = 32 x 4180 x 20
    = 2675200 Joules
    1kwh= 3600000
    therefore 2675200/3600000= 0.74 kwh..therefore total cost= .74*15= 11.15 cents Is my method correct???

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    Re: HSC 2012 Chemistry Marathon

    bump

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    Re: HSC 2012 Chemistry Marathon

    Yeah, looks right to me.
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    Re: HSC 2012 Chemistry Marathon

    I was wondering what the difference was between the dehydration of ethanol to ethylene and the hydration of ethylene to ethanol. Both use H2SO4 and I think dehydration uses conc. H2SO4 whereas hydration uses dilute H2SO4 but are there any other differences in the procedures? Thanks

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by Kimyia View Post
    I was wondering what the difference was between the dehydration of ethanol to ethylene and the hydration of ethylene to ethanol. Both use H2SO4 and I think dehydration uses conc. H2SO4 whereas hydration uses dilute H2SO4 but are there any other differences in the procedures? Thanks
    Dehydration uses slightly higher temperatures (350C) and concentrated sulfuric acid OR porous ceramic crystal OR zeolite catalyst.
    Hydration uses slightly lower temperatures (300C), dilute sulfuric acid OR highly acidic zeolite catalyst and high pressures.

    Even with these differences, the process is rather similar and all you really need to remember is that they both have ~300C temperature and concentrated/dilute sulfuric acid catalysts. Another obvious difference is that one reaction is the reverse of the other.

    Catalyst is needed in both is essentially the typical reason, very slow reaction if no catalyst is present.
    Last edited by someth1ng; 1 Mar 2012 at 7:48 PM.
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    Re: HSC 2012 Chemistry Marathon

    Question:

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    Re: HSC 2012 Chemistry Marathon

    Guys for your trends in the periodic table, i suggest you use equations when stating that the top left forms basic oxides and top right forms acidic
    i.e
    SO2+H20 ---> H2S03 etc etc

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    Re: HSC 2012 Chemistry Marathon


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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by zeebobDD View Post
    Natural systems require buffers in order to perform optimally preventing diseases and problems from arising. A buffer is an equimolar solution of weak acid and it's conjugate base that resists change in pH when small amounts of acid or base are added. A natural system in which buffers exist is human blood.

    An amphiprotic substance is able to act as an acid or base (i.e. a proton donor or acceptor). A specific buffer consisting of an amphiprotic species in human blood is H2CO3/HCO3-. The buffer is vital in our blood as it maintains the pH between 7.35 - 7.45 preventing acidosis or alkylosis.

    There exists a chemical equilibrium of this buffer in our blood:
    H2CO3 -> HCO3- + H+

    When there is excess acid in our blood, i.e. pH < 7.35, the buffer system will favour the reverse reaction in order to decrease the concentration of hydrogen ions, the equilibrium position will shift to the left and hence increase the pH.

    When there is excess base in our blood, i.e. pH > 7.45, it will react with the hydrogen ions forming water:
    H+ + OH- -> H2O

    The system will favour the forward reaction to produce more hydrogen ions, the equilibrium position will shift to the right and hence decrease the pH.

    As H2CO3/HCO3- can act as both an acid or base dependant on the changes in pH of our blood, it is an amphiprotic substance that can act as a buffer in human blood.

    My questions still up there waiting for someone.
    Last edited by nightweaver066; 11 Mar 2012 at 5:57 PM.

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    Re: HSC 2012 Chemistry Marathon

    Does anyone know the dissociation rate of sulphurous acid as a percentage at standard temp and pressure? thanks
    ~

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by nightweaver066 View Post
    Question:
    Sulfuric Acid is a diprotic strong acid. Lavoisier defined acids as a non-metal compound containing oxygen. Since H2S04 contains oxygen and isnt a metal lavoisiers theory of acids clearly accepts H2s04 as an acid. Sir Humphry Davy stated acids as substances that contain replaceable hydrogen atoms, for when they real with metals, the metals appear to replace the hydrogen in the acid causing Hydrogen gas to be evolved. H2S04 + 2Na ----> Na2S04 + H2,

    The Arrhenius theory of acids stated that acids are substances that when they dissovled in water, they release hydrogen ions. When H2S04 is dissovled in H20

    H2S04+ H20 ---> H30+ + HS03- therefore sulfuric acid also statisfies Svante's theory of acid. Lowry-Bronsted theory of acids(current one), states that acids are proton donors ie if a substance has a greater tendency to donate a proton than a particular solvent, then in that solvent it will be an acid. H2S04 also statisfies this given theory, as it will donate a proton when H2S04+ H20 ---> H30+ + HS03-, thus sulfuric acid can be classified as an Acid by all theories.


    guys can you let me know if this will be 6 marks n what i need to do to make it better?
    [/FONT]

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    Re: HSC 2012 Chemistry Marathon

    Quote Originally Posted by zeebobDD View Post
    Sulfuric Acid is a diprotic strong acid. Lavoisier defined acids as a non-metal compound containing oxygen. Since H2S04 contains oxygen and isnt a metal lavoisiers theory of acids clearly accepts H2s04 as an acid. Sir Humphry Davy stated acids as substances that contain replaceable hydrogen atoms, for when they real with metals, the metals appear to replace the hydrogen in the acid causing Hydrogen gas to be evolved. H2S04 + 2Na ----> Na2S04 + H2,

    The Arrhenius theory of acids stated that acids are substances that when they dissovled in water, they release hydrogen ions. When H2S04 is dissovled in H20

    H2S04+ H20 ---> H30+ + HS03- therefore sulfuric acid also statisfies Svante's theory of acid. Lowry-Bronsted theory of acids(current one), states that acids are proton donors ie if a substance has a greater tendency to donate a proton than a particular solvent, then in that solvent it will be an acid. H2S04 also statisfies this given theory, as it will donate a proton when H2S04+ H20 ---> H30+ + HS03-, thus sulfuric acid can be classified as an Acid by all theories.


    guys can you let me know if this will be 6 marks n what i need to do to make it better?
    [/FONT]
    Content sounds pretty good, expression could be better (but this isn't english so i'm not going to criticise that lol).

    Lavoisier defined acids as containing oxygen as he found non-metal oxides which reacted to form acids in water, e.g. sulfuric acid. Then provide the equation of sulfur trioxide reacting with water.

    Stay consistent in your response! Unsure if this is that important but you said acids dissolve to form hydrogen ions, but in your chemical equation, you had sulfuric acid forming hydronium ions.

    The rest looks fine though.

    Comment on my answer whether it's worthy 6 marks or not?

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