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amandali

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Re: Chemistry Question Thread
« Reply #210 on: March 27, 2016, 09:25:17 am »
0
Hi can u check my response?
 - Is qualitative an indirect evidence and quantitative a direct evidence
 - Am i allowed to omit the spectator ions for carbonate, iron reaction (below)
- is it enough to know the effects of acid rain as the only qualitative evidence
-For "discuss" questions  i dont need a concluding statement right ?

There has been an increase in the concentration of the oxides of nitrogen and sulfur in the atmosphere. Assess both the evidence to support this statement and the need to monitor these oxides  8 marks

Oxides of sulfur has increased in concentration from burning sulfide ores to extract metals CuS(s) + O2(g) -->Cu(s) + SO2(g) which releases SO2(g)
Whereas, acidic oxides of Nitrogen has increased mainly due to internal combustion engines and coal burning power stations.
N2(g) + O2(g) -->2NO(g)
2NO(g) + O2(g) -->2NO2(g)

These oxides the react with the water in the atmosphere:
SO2 (g)  + H2O(l) -->H2SO3(aq)
2NO2(g) + H2O (l)-->HNO2(aq)  + HNO3 (aq)
The evidence for the increase in these oxides comes from both direct of measurements of gas concentrations in the atmosphere and indirectly through effect of the increase in acid rain due to these oxides. The quantitative measurements are accurate and reliable due to the development of technologies in recent time. For eg. levels of SO2 and NO2 gases measured by analysing the gases trapped in bubbles of Antarctic ice which is a sample of the atmosphere from the past 200 years.
The indirect evidence comes from the effects of acid rain formed by these oxides. The acids H2SO3(aq) and HNO2(aq)/HNO3(aq) react and dissolves carbonates, which destructs historically important buildings and statues made of limestone and marble thus this becomes a record for the increase in levels of these oxides. 2H+(aq)+CaCO3(s)-->CO2(g) + H2O(l)+ Ca2+(aq) . Steel bridges and other steel structures also show evidence of damage due to acid rain since it reacts iron and dissolves it. 2H+(aq)+ Fe(s)-->H2(g)+Fe2+(aq). However, these evidences are less reliable as they could be resulted due to other oxides or factors.   

It is vital to record the monitor and record increasing levels of pollution so that we will know when to act and reduce the levels of NOx and SO2 as they are respiratory irritants therefore can cause asthma and other respiratory diseases and thus have a devastating impact on population’s health. They also lead to formation of acid rain which will cause cuticle on leaves to strip off leading to degradation of forest.

Overall, the direct and indirect evidence both shows the increase in concentration of these oxides, however, they are not completely reliable as the concentration of oxides changes over time and they are not representative of all parts of the world.

Happy Physics Land

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Re: Chemistry Question Thread
« Reply #211 on: March 27, 2016, 01:05:28 pm »
+3
Hi can u check my response?
 - Is qualitative an indirect evidence and quantitative a direct evidence
 - Am i allowed to omit the spectator ions for carbonate, iron reaction (below)
- is it enough to know the effects of acid rain as the only qualitative evidence
-For "discuss" questions  i dont need a concluding statement right ?

There has been an increase in the concentration of the oxides of nitrogen and sulfur in the atmosphere. Assess both the evidence to support this statement and the need to monitor these oxides  8 marks

Oxides of sulfur has increased in concentration from burning sulfide ores to extract metals CuS(s) + O2(g) -->Cu(s) + SO2(g) which releases SO2(g)
Whereas, acidic oxides of Nitrogen has increased mainly due to internal combustion engines and coal burning power stations.
N2(g) + O2(g) -->2NO(g)
2NO(g) + O2(g) -->2NO2(g)

These oxides the react with the water in the atmosphere:
SO2 (g)  + H2O(l) -->H2SO3(aq)
2NO2(g) + H2O (l)-->HNO2(aq)  + HNO3 (aq)
The evidence for the increase in these oxides comes from both direct of measurements of gas concentrations in the atmosphere and indirectly through effect of the increase in acid rain due to these oxides. The quantitative measurements are accurate and reliable due to the development of technologies in recent time. For eg. levels of SO2 and NO2 gases measured by analysing the gases trapped in bubbles of Antarctic ice which is a sample of the atmosphere from the past 200 years.
The indirect evidence comes from the effects of acid rain formed by these oxides. The acids H2SO3(aq) and HNO2(aq)/HNO3(aq) react and dissolves carbonates, which destructs historically important buildings and statues made of limestone and marble thus this becomes a record for the increase in levels of these oxides. 2H+(aq)+CaCO3(s)-->CO2(g) + H2O(l)+ Ca2+(aq) . Steel bridges and other steel structures also show evidence of damage due to acid rain since it reacts iron and dissolves it. 2H+(aq)+ Fe(s)-->H2(g)+Fe2+(aq). However, these evidences are less reliable as they could be resulted due to other oxides or factors.   

It is vital to record the monitor and record increasing levels of pollution so that we will know when to act and reduce the levels of NOx and SO2 as they are respiratory irritants therefore can cause asthma and other respiratory diseases and thus have a devastating impact on population’s health. They also lead to formation of acid rain which will cause cuticle on leaves to strip off leading to degradation of forest.

Overall, the direct and indirect evidence both shows the increase in concentration of these oxides, however, they are not completely reliable as the concentration of oxides changes over time and they are not representative of all parts of the world.

Hey Amanda!

I will just start off answering your questions first:
1. Both qualitative and quantitative are direct evidences (not necessarily first-hand evidences though!). Qualitative requires you to describe this evidence. So for example in this case if you mentioned photochemical smog, you would need to account for this evidence and explain how this evidence affects monitoring oxide levels in the future. Quantitative evidence requires numbers, either from data that the question perhaps gives you in an exam or from data you've already known beforehand. Just making up some statistics here, for example you can say about 100000 tonnes of nitrogen oxides are contributed by internal combustion engines or 5000 tonnes of nitrogen oxides are measured to be released everyday or something like that.

2. With extended response questions like this, unless they ask you for a net ionic equation, you only need to include a balanced chemical equation. Of course, it is up to you whether you would want to delete spectator ions or not! For me, I usually wouldnt unless the spectator ions really causes confusion.

3. No definitely not! Know at least 3 evidences, because questions like "assess the evidence for nitrogen oxides/sulfur oxides" are extremely common in exams. You would need around 3-4 evidences and account for those evidences and what they suggest about what we should do in the future to produce less of those oxides. Some evidences are NOAA flask and gas chromatograph measurements, increase in coal burning power plants and photochemical smog. There! You already have 3 more evidences besides acid rain!

4. Personally I do, but it doesnt make such a big impact upon your final mark for the response if you dont include a concluding statement. You've gotta present both sides (i.e. positive and negative) of the question and then have one short last sentence that expresses your opinion (e.g. the benefits of _______ outweighs the disadvantages of ________ and hence _________ definitely benefits the society more).

Ok so I've had a look at your response now, and I will just point out some of the good stuff and some of those not-so-good stuff that you can improve on. But look, overall I reckon this would be a response somewhere between band 5 - band 6, and your teacher might choose to give you a high band 5. You have fluently illustrated what the question asks you to do and demonstrated a good understanding of those evidences and their impacts. You have in your establishing sentences accounted for the occurrence of your acidic rain and stated briefly the reason for concentrations of these oxides in atmosphere (to be brief with these things is good because they dont directly answer the question but you are providing examiners with backgrounds). I must also applaud you on your assessment of the evidences which is the question! Many candidates would forget or include very little judgments in their responses. What I often tell people to do is in the end just explicitly state the word judgment and state what your judgment is (i.e.  "Judgment: __________________________"). It sounds a bit clumsy but it tells the teacher you are answering the assess part of the question!

Ok now lets move onto the defects of your response. The biggest defect in your response is that your evidences are limited. You have mentioned two evidences: gas measurement and a whole tonne of info on acidic rain. This imbalance between the amount of explanation you put on gas measurement and the amount of explanation you put on acidic rain makes the examiner feel like "okay so this girl really knows her acidic rain stuff but she's just stating this gas measurement for the sake of stating it". I would recommend to either take out some information about acid rains and put more information into gas measurement. Or you can just simply add more information in gas measurement. To make your response stronger, you should really include another evidence such as photochemical smog.

Another defect is about your monitoring part of the question. You have used cause and effect language to explain the need for monitoring these acidic oxides but like what I said before, you are focusing a little too much on the evidence part and you are not balancing out your monitoring part. You can add one more point about the necessity to monitor these oxides (for example Nitrogen oxide's greenhouse effect is 100 times stronger than carbon dioxides) and you can also relate photochemical smog to your statement of acidic oxides being respiratory irritants.

Ok so out of 8 I would give a 6-7/8, and your teacher would most likely give you a mark like that as well (definitely not anything below 6). Overall its a very good piece of writing, well done! :D

Best Regards
Happy Physics Land
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katherine123

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Re: Chemistry Question Thread
« Reply #212 on: March 27, 2016, 01:32:15 pm »
0
Please check my response thanks
Is initiator and catalyst the same (organic peroxide for the production of LDPE)?


Analyse why ethylene is such as important starting material for the chemical industry, in your answer, include relevant chemical equations, and a description of new materials and fuels that can be prepared from ethylene. 7 marks

Ethene contains a reactive double bond which enables it to react readily with many substances forming polyethylene which is a starting material for plastics, a useful product which is widely used to make lives easier
[CH2CH2]n --> -[CH2-CH2-]-
The 2 types of polyethylene include LDPE and HDPE. HDPE is produced at a low gas pressure and temperature of 60 degrees with a Ziegler Natta catalyst. The catalyst attaches to the monomers which enable monomers to link and form a long chain. Once the activated chains collide, the chain growth stops and polyethylene is formed with an unbranched, crystalline structure which makes it rigid and brittle. Thus, it is used to make garbage bins, toys and garbage bags. LDPE is also produced in a similar way but under high gas pressure and temperature of 300 degrees with organic peroxide initiator. The chains formed are branched thus cannot pack closely together like HDPE which makes it soft and flexible. Hence, it is used to make glab wraps and plastic squeeze bottles.

It can also be converted to ethanol by heating it with steam at 300 degrees and high pressure using phosphoric catalyst as the catalyst. CH2CH2(g) + H20(l) --> CH3CH2OH(aq). Ethanol is a useful solvent for  perfume, cosmetics, and paints. Although the ethanol that is currently used as a fuel blend originates from fermentation of sugary crops, ethanol may be sourced from ethene in the future if a more economic method for its production is developed.

amandali

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Re: Chemistry Question Thread
« Reply #213 on: March 27, 2016, 04:41:17 pm »
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Hey Amanda!

I will just start off answering your questions first:
1. Both qualitative and quantitative are direct evidences (not necessarily first-hand evidences though!). Qualitative requires you to describe this evidence. So for example in this case if you mentioned photochemical smog, you would need to account for this evidence and explain how this evidence affects monitoring oxide levels in the future. Quantitative evidence requires numbers, either from data that the question perhaps gives you in an exam or from data you've already known beforehand. Just making up some statistics here, for example you can say about 100000 tonnes of nitrogen oxides are contributed by internal combustion engines or 5000 tonnes of nitrogen oxides are measured to be released everyday or something like that.

2. With extended response questions like this, unless they ask you for a net ionic equation, you only need to include a balanced chemical equation. Of course, it is up to you whether you would want to delete spectator ions or not! For me, I usually wouldnt unless the spectator ions really causes confusion.

3. No definitely not! Know at least 3 evidences, because questions like "assess the evidence for nitrogen oxides/sulfur oxides" are extremely common in exams. You would need around 3-4 evidences and account for those evidences and what they suggest about what we should do in the future to produce less of those oxides. Some evidences are NOAA flask and gas chromatograph measurements, increase in coal burning power plants and photochemical smog. There! You already have 3 more evidences besides acid rain!

4. Personally I do, but it doesnt make such a big impact upon your final mark for the response if you dont include a concluding statement. You've gotta present both sides (i.e. positive and negative) of the question and then have one short last sentence that expresses your opinion (e.g. the benefits of _______ outweighs the disadvantages of ________ and hence _________ definitely benefits the society more).

Ok so I've had a look at your response now, and I will just point out some of the good stuff and some of those not-so-good stuff that you can improve on. But look, overall I reckon this would be a response somewhere between band 5 - band 6, and your teacher might choose to give you a high band 5. You have fluently illustrated what the question asks you to do and demonstrated a good understanding of those evidences and their impacts. You have in your establishing sentences accounted for the occurrence of your acidic rain and stated briefly the reason for concentrations of these oxides in atmosphere (to be brief with these things is good because they dont directly answer the question but you are providing examiners with backgrounds). I must also applaud you on your assessment of the evidences which is the question! Many candidates would forget or include very little judgments in their responses. What I often tell people to do is in the end just explicitly state the word judgment and state what your judgment is (i.e.  "Judgment: __________________________"). It sounds a bit clumsy but it tells the teacher you are answering the assess part of the question!

Ok now lets move onto the defects of your response. The biggest defect in your response is that your evidences are limited. You have mentioned two evidences: gas measurement and a whole tonne of info on acidic rain. This imbalance between the amount of explanation you put on gas measurement and the amount of explanation you put on acidic rain makes the examiner feel like "okay so this girl really knows her acidic rain stuff but she's just stating this gas measurement for the sake of stating it". I would recommend to either take out some information about acid rains and put more information into gas measurement. Or you can just simply add more information in gas measurement. To make your response stronger, you should really include another evidence such as photochemical smog.

Another defect is about your monitoring part of the question. You have used cause and effect language to explain the need for monitoring these acidic oxides but like what I said before, you are focusing a little too much on the evidence part and you are not balancing out your monitoring part. You can add one more point about the necessity to monitor these oxides (for example Nitrogen oxide's greenhouse effect is 100 times stronger than carbon dioxides) and you can also relate photochemical smog to your statement of acidic oxides being respiratory irritants.

Ok so out of 8 I would give a 6-7/8, and your teacher would most likely give you a mark like that as well (definitely not anything below 6). Overall its a very good piece of writing, well done! :D

Best Regards
Happy Physics Land

Is it sufficient if i add this to the gas measurement
Moreover, direct measurements are made by statutory bodies such as NSW EPA and scientists researching the atmosphere. NOx were found to be part of pollution generated over large cities due to use of internal combustion engines since industrial revolution


NOx produces photochemical smog after reacting in the presence of sunlight which is a toxic pollutant that causes respiratory diseases

jakesilove

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Re: Chemistry Question Thread
« Reply #214 on: March 27, 2016, 05:14:21 pm »
+1
Please check my response thanks
Is initiator and catalyst the same (organic peroxide for the production of LDPE)?


Analyse why ethylene is such as important starting material for the chemical industry, in your answer, include relevant chemical equations, and a description of new materials and fuels that can be prepared from ethylene. 7 marks

Ethene contains a reactive double bond which enables it to react readily with many substances forming polyethylene which is a starting material for plastics, a useful product which is widely used to make lives easier
[CH2CH2]n --> -[CH2-CH2-]-
The 2 types of polyethylene include LDPE and HDPE. HDPE is produced at a low gas pressure and temperature of 60 degrees with a Ziegler Natta catalyst. The catalyst attaches to the monomers which enable monomers to link and form a long chain. Once the activated chains collide, the chain growth stops and polyethylene is formed with an unbranched, crystalline structure which makes it rigid and brittle. Thus, it is used to make garbage bins, toys and garbage bags. LDPE is also produced in a similar way but under high gas pressure and temperature of 300 degrees with organic peroxide initiator. The chains formed are branched thus cannot pack closely together like HDPE which makes it soft and flexible. Hence, it is used to make glab wraps and plastic squeeze bottles.

It can also be converted to ethanol by heating it with steam at 300 degrees and high pressure using phosphoric catalyst as the catalyst. CH2CH2(g) + H20(l) --> CH3CH2OH(aq). Ethanol is a useful solvent for  perfume, cosmetics, and paints. Although the ethanol that is currently used as a fuel blend originates from fermentation of sugary crops, ethanol may be sourced from ethene in the future if a more economic method for its production is developed.

Hey!

Yes, initiator and catalyst can be thought of as the same thing.

I like your answer; I think it goes into sufficient depth for most areas that you discuss. However, I would add something small about the PRODUCTION of ethene: Part of it's significance in the chemical industry is the ease by which it can be produced, particularly through catalytic cracking of fuel fractions. This is a really important reason as to why we love Ethene: not only is it great (as you've described) because of its reactivity, but also because of its potential abundance! Other than that, and perhaps rewording some of your sentences (read it outloud, and see if anything seems a bit rambly) I think you have covered lots of vital areas in answering the question.

Jake
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Happy Physics Land

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Re: Chemistry Question Thread
« Reply #215 on: March 27, 2016, 06:36:15 pm »
+1
Is it sufficient if i add this to the gas measurement
Moreover, direct measurements are made by statutory bodies such as NSW EPA and scientists researching the atmosphere. NOx were found to be part of pollution generated over large cities due to use of internal combustion engines since industrial revolution


NOx produces photochemical smog after reacting in the presence of sunlight which is a toxic pollutant that causes respiratory diseases

Hey Amanda!

Yes if you add these your response would sound way stronger! Because now you are accounting for your evidences more and proposing a bit more new ideas! Well done! To get a full 8/8 I reckon you can just add in a few examples of how to monitor those oxides (e.g. look up if theres a legislation regarding the release of NOx or SOx pollutants, and then you can say "because of these evidences which demonstrate the negative consequences of these oxides, hence these emissions must be monitored. For example, the government body has participated in this monitoring process through this legislation _________, " This just makes the teacher realise that you have a great insight into the question and displays understandings towards those monitoring actions.

Im gonna use an analogy here (hehe :) no hates ). For me, I reckon originally your response was like a finely-made cake with icings sprinkled everywhere. Now after you apply the feedback and added in those stuff your response is like a finely-made cake that is beautifully decorated with a layer of evenly distributed icing. So now what you have to do is to just sprinkle some rainbow coloured sugar thingy on top!

Best Regards
Happy Physics Land
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grace_joseph

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Re: Chemistry Question Thread
« Reply #216 on: March 27, 2016, 06:39:21 pm »
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Hi Jake,

Would you please be able to explain why this is the answer to the 2011 HSC paper q25 (attachment 1 and 2)? I don't really know why you need two equations, or even where the equations came from. I understand buffers but have never seen them proved using water before

Also, would you mind explaining question 15 of this paper to me when you could? (attachment 3) The answer is A :)

Thanks very much Jake :)

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Re: Chemistry Question Thread
« Reply #217 on: March 27, 2016, 07:07:10 pm »
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Hi Jake,

Would you please be able to explain why this is the answer to the 2011 HSC paper q25 (attachment 1 and 2)? I don't really know why you need two equations, or even where the equations came from. I understand buffers but have never seen them proved using water before

Also, would you mind explaining question 15 of this paper to me when you could? (attachment 3) The answer is A :)

Thanks very much Jake :)

Hey Grace!

Great question, as it really does seem like the equations were pulled out of nowhere! However, when you consider what a buffer is actually MEANT to do, the equations start to make sense!

A buffer is something that resists small changes in pH, which is vitally important for things like living organisms and cells. All the equations display are the acidic and basic nature of the buffer: in the first equation, you can clearly is the substance is a proton donor, whilst in the second you can clearly see that the substance is a proton acceptor. As such, the system can be both acidic and basic, and therefore resist small changes in pH! I hope that this makes sense: if you're ever unsure as to how to write out buffer equations, just add water to each part of the buffer and show the acidic and basic properties of the buffer!

As for Question 15, I don't think I can really answer it without the rest of the question. However, I assume that there are equal moles of strong and weak acid? In that case, remember that the important part of neutralisation reactions is the number of MOLES of the acid, as the number of moles of the base will need to equal that (in whatever ratio the chemical equation states) in order for neutralization to occur. For instance, a monoprotic WEAK acid of 0.1mol/L will require the same amount of NaOH to neutralise it as a monoprotic STRONG acid of 0.1mol/L, as the concentration is the important part in this reaction.

I hope this helps! Feel free to ask more questions so I can help clarify your understanding :)

Jake
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Re: Chemistry Question Thread
« Reply #218 on: March 27, 2016, 08:02:29 pm »
0
Hi Jake! Thank you very much for the buffer answer, yes I get it now :)

And sorry I forgot to add the first part of question 15! It's attached now but I still don't understand why a weak acid would require the same amount of base as a strong one, as when we do titrations I thought it was established that one drop of NaOH may overpower acetic acid but not have any effect on HCl?

Sorry! I really appreciate any help you can give, even if I still don't get it :D

Grace

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Re: Chemistry Question Thread
« Reply #219 on: March 27, 2016, 09:07:58 pm »
0
Justify the continued use of Arrhenius definition of acids and bases, despite the development of the more sophisticated Bronsted-Lowry definition 3 marks
how do these 2 definitions describe neutralization differently


Water and ethanol are both used as solvents. Explain the diff and sim. in their solvent behaviour in terms of their molecular structures. Include a diagram 4 marks
I wrote my answer in a table (similarities+differences)
Is there anything else i can add to differences or is that sufficient
Similarities
•   Both water and ethanol are polar molecules
•   Both consists of polar hydroxyl group (-OH) which can attract and dissolve polar substances eg. HCl through dipole-dipole attraction, hydrogen bonding or dispersion forces.

differences
•   Ethanol has a non-polar region ie ethyl group (-CH2CH3) whereas water does not thus only ethanol can dissolve (some) non-polar substances eg. Hexane via dispersion forces. Water does not have non-polar regions therefore is a poor solvent for non-polar substances

Including a diagram of ethanol attract both polar and non-polar sub. and water attracting polar sub.

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Re: Chemistry Question Thread
« Reply #220 on: March 27, 2016, 10:36:47 pm »
0
Hi Jake! Thank you very much for the buffer answer, yes I get it now :)

And sorry I forgot to add the first part of question 15! It's attached now but I still don't understand why a weak acid would require the same amount of base as a strong one, as when we do titrations I thought it was established that one drop of NaOH may overpower acetic acid but not have any effect on HCl?

Sorry! I really appreciate any help you can give, even if I still don't get it :D

Grace

Hey Grace!

When it comes to titrations, it is the Mol/L that is important. Think about it this way: let's pretend I titrate 25mL of monoprotic acid (0.1mol/L) with XmL of monoprotic base (0.1mol/L).

The equation is something like Acid + Base --> Salt + Water, and the ratio of Acid:Base will be 1:1.

Using our formulas, we know that 25mL of 0.1 mol/L acid will contain 0.0025 moles (0.1*0.025). Because it is a 1:1 reaction, we require 0.0025 moles of base, which will require a quantity of 25mL (as expected).

However, nowhere here did we discuss what specific acids or bases we used! The only important thing is the concentration: you can have a really concentrated weak acid, and a very dilute strong acid! It would be EASIER to have a strong, concentrated acid, but definitely not necessary. When it comes to Titrations, only the numbers matter.

Jake
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Re: Chemistry Question Thread
« Reply #221 on: March 27, 2016, 10:46:05 pm »
+3
Hey!

Yes, initiator and catalyst can be thought of as the same thing.

I like your answer; I think it goes into sufficient depth for most areas that you discuss. However, I would add something small about the PRODUCTION of ethene: Part of it's significance in the chemical industry is the ease by which it can be produced, particularly through catalytic cracking of fuel fractions. This is a really important reason as to why we love Ethene: not only is it great (as you've described) because of its reactivity, but also because of its potential abundance! Other than that, and perhaps rewording some of your sentences (read it outloud, and see if anything seems a bit rambly) I think you have covered lots of vital areas in answering the question.

Jake

Just popping in some chat Jake...

I didn't even realise that the peroxide initiator in LDPE and catalyst in HDPE worked the same way until AFTER the HSC!!

amandali

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Re: Chemistry Question Thread
« Reply #222 on: March 28, 2016, 01:40:52 am »
0
Please check my response thanks
Evaluate the success of the current usage of ethanol as an alternative car fuel obtained from sugar cane 4 marks

Currently, ethanol is used directly as a fuel in Brazil as there is enough arable land to grow sugary crops from which ethanol is derived. The advantage of ethanol is that it is renewable and abundant as it is produced from the fermentation of crops such as sugar cane, corn, wheats, C6H12O6 (aq) --> 2CH3CH2OH(aq) + 2CO2 (g)  , as opposed to the hydrocarbon fuels like octane which is produced from non-renewable fossil fuels.  Hence, ethanol has an unlimited use while hydrocarbon fuels are limited and are predicted to deplete within the next few decades. Moreover, ethanol combusts cleanly due to presence of oxygen in its molecule which enables a more complete combustion. This mean that less harmful respiratory irritants like C(s) and CO(g) that causes respiratory diseases are produced.
 CH3CH2OH(l) + 3O2 (g) --> 2CO2 (g) + 3H2O(l) .

Meanwhile, it is not widely used countries like Australia as it lacks arable land to grow sugary crops and it is not economical to produce ethanol. The disadvantage of ethanol is that its production requires cultivating and clearing vast areas of arable land hence this will affect food production and give rise to environmental effects such as land erosion and destruction of animal habitats. An immense amount of energy is also required to manufacture fertilisers, plant and harvest the crop and distil ethanol thus it is not economically viable to do so.

Weighing the pros and cons, it is unlikely that ethanol will not be used as an alternative fuel unless an economic viable method for converting cellulose to glucose is discovered.

jakesilove

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Re: Chemistry Question Thread
« Reply #223 on: March 28, 2016, 11:18:40 am »
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Please check my response thanks
Evaluate the success of the current usage of ethanol as an alternative car fuel obtained from sugar cane 4 marks

Currently, ethanol is used directly as a fuel in Brazil as there is enough arable land to grow sugary crops from which ethanol is derived. The advantage of ethanol is that it is renewable and abundant as it is produced from the fermentation of crops such as sugar cane, corn, wheats, C6H12O6 (aq) --> 2CH3CH2OH(aq) + 2CO2 (g)  , as opposed to the hydrocarbon fuels like octane which is produced from non-renewable fossil fuels.  Hence, ethanol has an unlimited use while hydrocarbon fuels are limited and are predicted to deplete within the next few decades. Moreover, ethanol combusts cleanly due to presence of oxygen in its molecule which enables a more complete combustion. This mean that less harmful respiratory irritants like C(s) and CO(g) that causes respiratory diseases are produced.
 CH3CH2OH(l) + 3O2 (g) --> 2CO2 (g) + 3H2O(l) .

Meanwhile, it is not widely used countries like Australia as it lacks arable land to grow sugary crops and it is not economical to produce ethanol. The disadvantage of ethanol is that its production requires cultivating and clearing vast areas of arable land hence this will affect food production and give rise to environmental effects such as land erosion and destruction of animal habitats. An immense amount of energy is also required to manufacture fertilisers, plant and harvest the crop and distil ethanol thus it is not economically viable to do so.

Weighing the pros and cons, it is unlikely that ethanol will not be used as an alternative fuel unless an economic viable method for converting cellulose to glucose is discovered.

Hey Amanda,

I would add in some more aspects of ethanol as an ALTERNATIVE CAR FUEL, specifically things like the erosion of engines, specific heat capacity etc. that effects its current usage in Australia (limiting it to E10 etc.). Other than that, a really good response.

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Re: Chemistry Question Thread
« Reply #224 on: March 28, 2016, 12:50:39 pm »
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how do you know that there is change in pressure?  i know that change in concentration is indicated by sharp drop or increase

at 10min can it be increase in temperature as well (endothermic)  although its due to increase in CO concentration as indicated by the sharp increase