Help with monitoring combustion reactions (1 Viewer)

[bs101]

This was a question from the 2014 HSC chem paper:

Under conditions of low oxygen levels, octane can undergo incomplete combustion according to the following chemical equation:

2C8H18(l) + 17O2(g) --> 6C(s) + 4CO(g) + 6CO2(g) + 18H2O(l)

a) explain the need to monitor this process

This is what i wrote as my answer: It is essential to monitor the combustion of octane as incomplete combustion can result in:
- the release of CO (carbon monoxide), which is an air pollutant and can cause respiratory irritation
- C (carbon soot) is produced, which is also an air pollutant
- incomplete combustion releases less energy per mole of fuel burnt
Thus, due to the production of C, CO and less release of energy, combustion reactions need to be monitored

I got 0/2 for that question - was this mark justified? or what did i do wrong/how could i have improved my answer?

Any help would be greatly appreciated!

 

[Librah]

This was a question from the 2014 HSC chem paper:

Under conditions of low oxygen levels, octane can undergo incomplete combustion according to the following chemical equation:

2C8H18(l) + 17O2(g) --> 6C(s) + 4CO(g) + 6CO2(g) + 18H2O(l)

a) explain the need to monitor this process

This is what i wrote as my answer: It is essential to monitor the combustion of octane as incomplete combustion can result in:
- the release of CO (carbon monoxide), which is an air pollutant and can cause respiratory irritation
- C (carbon soot) is produced, which is also an air pollutant
- incomplete combustion releases less energy per mole of fuel burnt
Thus, due to the production of C, CO and less release of energy, combustion reactions need to be monitored

I got 0/2 for that question - was this mark justified? or what did i do wrong/how could i have improved my answer?

Any help would be greatly appreciated!

Is that your exact response? Need the original to actually judge on this, word for word. I got 2/2 for this btw.

 

[bs101]

Word for word it's:

It is essential to monitor the combustion of octane as if incomplete combustion occurs:
- CO (carbon monoxide) is produced, which is an air pollutant and can cause respiratory irritation
- C (carbon soot) is produced, which is also an air pollutant
- incomplete combustion releases less energy per mole of fuel burnt
Thus, due to the production of C, CO and less release of energy, combustion reactions need to be monitored

 

[Librah]

Word for word it's:

It is essential to monitor the combustion of octane as if incomplete combustion occurs:
- CO (carbon monoxide) is produced, which is an air pollutant and can cause respiratory irritation
- C (carbon soot) is produced, which is also an air pollutant
- incomplete combustion releases less energy per mole of fuel burnt
Thus, due to the production of C, CO and less release of energy, combustion reactions need to be monitored

Your not answering the question initially... It's already given that it's incomplete combustion, there was no real point in identifying what the products were, you just had to give a reason why it was explain why it had to be monitored. Also during incomplete combustion it is not guranteed that carbon will be released.

 

[faisalabdul16]

I think you didn't explain enough.

The products of incomplete combustion need to be carefully monitored because of the harmful and unwanted products produced, carbon monoxide and carbon. Carbon monoxide has the ability to alter blood pH and reduces oxygen carrying capacity of haemoglobin molecules. Carbon is a carcinogen which can cause detrimental cancers. Thus, it is essential to monitor the products of incomplete combustion reactions as they have detrimental impacts upon society.

 

[bs101]

I put in carbon because in the equation given carbon was produced (and the question asked for this process so i thought i would be referencing the eqn). Also, i just restated if incomplete combustion occurs...*list reasons* - isn't that what the question is asking given that it is incomplete and that's why you need to monitor it? Not sure if any of the information was irrelevant or contradicted each other but should i really get 0 for it? (btw thanks for the fast response )

edit: well i'm looking online now and it does say that black carbon belongs to a class of air pollutants called particulate matter (like you said) - but it is still an air pollutant? maybe i should have explained it further like faisalabdul16 said or just touched on the risks. Either way, i don't know if that should have cost me 2 marks

 

[faisalabdul16]

I don't think HSC markers will actually expect you to rote that much information lol. Also carbon (soot) as a pollutant isn't really valid, as it is as much pollutant as any other particulate matter or even carbon dioxide, the only difference is the quantity released. It's like saying noise is a pollutant during the Solvay or Haber process that annoys birds and wildlife.

it's not rote, just a combination of biology and chemistry but i guess it may come off as rote...

Why wouldn't carbon be valid? It is carcinogenic...

 

[Librah]

I put in carbon because in the equation given carbon was produced (and the question asked for this process so i thought i would be referencing the eqn). Also, i just restated if incomplete combustion occurs...*list reasons* - isn't that what the question is asking given that it is incomplete and that's why you need to monitor it? Not sure if any of the information was irrelevant or contradicted each other but should i really get 0 for it? (btw thanks for the fast response )

It was a very sketchy response, you kind of waffled a little bit and looked like you were trying to fill in some space. But the point i was making here, was that the way you worded it was as if you were saying Carbon (soot) is ALWAYS produced. Have to watch out the way you word your response or it may be a bit ambiguous.

 

[Librah]

it's not rote, just a combination of biology and chemistry but i guess it may come off as rote...

Why wouldn't carbon be valid? It is carcinogenic...

There are many other things that can be carcinogenic, listing one among a million isn't really a good thing to do, but Hsc will probably accept it since it's the main carcinogenic source when referring to society.

 

[Kaido]

->justification as to why it's a pollutant
->back up reason for incomplete combustion (show that insufficient oxygen on the left side etc.)
->explanation as to how to monitor energy,oxygen,environmental impacts etc.
->costs and how it affects society if not monitored

(3 of these should do for 2 marks)

isn't ur hsc over lol

 

[Kaido]

lol, you dont 'lose' marks for putting irrelevant info. you only score marks... (or so i'm told)

the lesson is: pour everything you know onto that piece of paper, ggwp (too late now, haha)

 

[InteGrand]

lol, you dont 'lose' marks for putting irrelevant info. you only score marks... (or so i'm told)

the lesson is: pour everything you know onto that piece of paper, ggwp (too late now, haha)

lol look at the marking criteria for 2013 HSC Chemistry long responses: http://www.boardofstudies.nsw.edu.au/hsc_exams/2013/pdf_doc/2013-marking-guide-chemistry.pdf

This was required to get 7/7 in any of the Option 7-markers: "Coherent, concise response with no irrelevant extraneous information"

Also, they usually want logical and coherent responses for long responses. This was required for a 6-marker in that 2013 paper: "Response should demonstrate coherency and present information in a logical way".

So if a response is too long, it gives them an excuse to take off a mark if they want.

The problem is, we don't know the marking criteria beforehand, so we don't know what info they want, causing us to put in as much info as possible.

 

[Kaido]

Yer nah you do lose marks lol. Waffling is something HSC markers really discourage, note my physics extended response, if they actually gave marks for putting irrelevant info, i'd be getting full marks all around. But 2/5 3/5 4/6 3/6. I think that's one of the reasons so many people expect a higher mark than they thought they got for chemistry, content dumping on paper won't give you much(sometimes instant 0, or if they spot a key word 1 mark/7)

no, i think u misinterpreted. you dont score marks for irrelevant info, nor do you lose marks (but integrand says otherwise for long responses). you score marks if you meet the marking criteria

but then again, i'm just a noob at these hsc thingys

 

[Librah]

no, i think u misinterpreted. you dont score marks for irrelevant info, nor do you lose marks (but integrand says otherwise for long responses). you score marks if you meet the marking criteria

but then again, i'm just a noob at these hsc thingys

Not entirely sure, but you don't lose marks for adding extra info that is actually answering the question e.g if you include relevant chemical equations when they don't ask for it, since it's expected you do as it's a chemistry course.

 

[Kaido]

Alright, i'll note that down
Thanks Yun
(and integrand)

 

[someth1ng]

Not gonna lie, YunLi has given has poor advice here.

I don't think HSC markers will actually expect you to rote that much information lol. Also carbon (soot) as a pollutant isn't really valid, as it is as much pollutant as any other particulate matter or even carbon dioxide, the only difference is the quantity released. It's like saying noise is a pollutant during the Solvay or Haber process that annoys birds and wildlife.

Pretty standard for HSC chemistry and soot is definitely valid given the context because we're talking about combustion so significant amounts of soot can be released in a fair small area so it must be monitored.

Yer nah you do lose marks lol. Waffling is something HSC markers really discourage, note my physics extended response, if they actually gave marks for putting irrelevant info, i'd be getting full marks all around. But 2/5 3/5 4/6 3/6. I think that's one of the reasons so many people expect a higher mark than they thought they got for chemistry, content dumping on paper won't give you much(sometimes instant 0, or if they spot a key word 1 mark/7)

You lose marks by not satisfying the marking criteria - if you look at how the criteria works, missing 1 piece of information can drop you down to 1/6 because they set a minimum for each grade you can get. You don't lose more than 1-2 marks for not being coherent and concise.

It is essential to monitor the combustion of octane as incomplete combustion can result in:
- the release of CO (carbon monoxide), which is an air pollutant and can cause respiratory irritation
- C (carbon soot) is produced, which is also an air pollutant
- incomplete combustion releases less energy per mole of fuel burnt
Thus, due to the production of C, CO and less release of energy, combustion reactions need to be monitored

You have a really crap reason for CO - the main reason why you need to monitor CO is because it's very toxic at fairly low concentrations (about 1% is enough to kill you) and when having a process that occurs on a large scale, these low concentrations are relatively easy to achieve. Soot is a problem because it's a respiratory irritant, especially when there's significant amounts of it - think of the exhaust of a truck, doesn't really smell nice, makes it hard to breathe, is carcinogenic, and causes cardiovascular problems. For the last point, you need to remember that the question says "need" - you don't really "need" more energy released, that's more of a desire but if you go down that path, you'll need to say less than what - less energy is released than what? So yeah, 0/2 is the correct amount of marks given.

 

[Kaido]

Will listen to chuck norris

 

[Librah]

Not gonna lie, YunLi has given has poor advice here.


Pretty standard for HSC chemistry and soot is definitely valid given the context because we're talking about combustion so significant amounts of soot can be released in a fair small area so it must be monitored. Missing specific criteria does lose marks, so have to agree on that but I didn't mention that in the context of this thread. However I just gave the fastest response I could and I admit I couldve analyzed it a bit better.

Should probably listen to norris on this one.


You lose marks by not satisfying the marking criteria - if you look at how the criteria works, missing 1 piece of information can drop you down to 1/6 because they set a minimum for each grade you can get. You don't lose more than 1-2 marks for not being coherent and concise.


You have a really crap reason for CO - the main reason why you need to monitor CO is because it's very toxic at fairly low concentrations (about 1% is enough to kill you) and when having a process that occurs on a large scale, these low concentrations are relatively easy to achieve. Soot is a problem because it's a respiratory irritant, especially when there's significant amounts of it - think of the exhaust of a truck, doesn't really smell nice, makes it hard to breathe, is carcinogenic, and causes cardiovascular problems. For the last point, you need to remember that the question says "need" - you don't really "need" more energy released, that's more of a desire but if you go down that path, you'll need to say less than what - less energy is released than what? So yeah, 0/2 is the correct amount of marks given.

Should have probably put a footnote here, but these are simply just things ive come to conclude from questions some others and I have lost marks for. Also for the soot part, I corrected myself in response to faisal about the context. Admittedly i did rush some of these responses since i was juggling from this thread to non-school section, so i'll fix/delete some misleading posts. P.S: some of my posts may have been a bit exaggerated.

In the end, i'd trust someone more experienced to give advice, so i'd follow Norris here. Given that i just completed my HSC this year.

 

[someth1ng]

Should have probably put a footnote here, but these are simply just things ive come to conclude from questions some others and I have lost marks for. Also for the soot part, I corrected myself in response to faisal about the context. Admittedly i did rush some of these responses since i was juggling from this thread to non-school section, so i'll fix/delete some misleading posts. P.S: some of my posts may have been a bit exaggerated.

In the end, i'd trust someone more experienced to give advice, so i'd follow Norris here. Given that i just completed my HSC this year.

That's fair enough, it does happen that our explanations can go a bit off when we try to push some point. Anyway, I would never require you to trust me simply because I am more experienced, it's definitely more important to be able to read someone else's response(s) and determine whether it's something worth learning from or not.