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Edexcel - Chemistry Unit 2 - 4 June 2013

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Original post by James A
You need to refer specifically that the C=O pattern is seen in the product but not present in the alcohol. Then you could also add that the OH broad peak is not present in the product but only present in the alcohol, just to secure your marks.


C=O stretching in ketones*

A lack of O-H peak for alcohols will surely suffice
Reply 1721
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SKK94
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Original post by ALevel96
C=O stretching in ketones*

A lack of O-H peak for alcohols will surely suffice


In this question, I accidentally said 'absorption spectra' instead of 'infrared spectra'
Could I lose a mark for that ? :frown:
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Original post by shan94
Hi I put redox but I was unsure between nucleophilic sub and redox :s-smilie:
What did u put? :smile:


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i put nuc sub?:frown: confused:frown:
Clearly was nucleophillic substitution. (see where I've highlighted)

Phew! 1 mark saved there!

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1370611718079.jpg35.7KB
Original post by geor
Do you mean 19?
It doesn't matter how much energy is released per tonne of biofuel as this has no correlation with CO2 emissions. However, it does matter how much energy we USE to make the biofuel, as that energy has probably come from fossil fuels which release CO2 when they are burned. Biofuels require pesticides and fertilisers to be grown, which require energy to make and hence CO2 will be produced. Therefore it is not B.

The fact about pesticides/fertilisers making biofuels not carbon neutral is in a past mark scheme I think. I am sure this answer is C.



Hi, I am sure the answer is B. A definition of carbon neutral is that the amount of CO2 produced in it manufacture, combustion, transport etc, taken away from the growth of the plant is 0. So using fertilizers to grow the crops is not part of that, so thane answer is B.
Original post by Hi, How are you ?
Hi, I am sure the answer is B. A definition of carbon neutral is that the amount of CO2 produced in it manufacture, combustion, transport etc, taken away from the growth of the plant is 0. So using fertilizers to grow the crops is not part of that, so thane answer is B.


Using fertilisers IS part of the definition of Carbon Neutral, because CO2 must have been used for the production of the fertilizers!

Answer is C.
Original post by Hi, How are you ?
Hi, I am sure the answer is B. A definition of carbon neutral is that the amount of CO2 produced in it manufacture, combustion, transport etc, taken away from the growth of the plant is 0. So using fertilizers to grow the crops is not part of that, so thane answer is B.


Some fertilizers have a carbon footprint that has not being considered. So this is also added! My teacher said so....


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Original post by Hi, How are you ?
Hi, I am sure the answer is B. A definition of carbon neutral is that the amount of CO2 produced in it manufacture, combustion, transport etc, taken away from the growth of the plant is 0. So using fertilizers to grow the crops is not part of that, so thane answer is B.


It's C I'm afraid; the amount of energy released has nothing to do with the carbon footpront, however fertiliser production does. Think of the Haber process (making ammonia, which is then used for fertiliser production); although no carbon-containing molecules are used in the actual formation of the ammonia, the combustion of methane is often used to provide the H2, but also releases CO2.
Reply 1728
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ayat94
who ever is doing unit 4 chemistry can someone please help me with these two questions please ?

2. Consider the following equation:
2SO2 + O2 arrow 2SO3
2.0 moles of SO2 and 1.0 mole of O2 were allowed to react in a vessel of volume 60 dm3.
At equilibrium 1.8 moles of SO3 had formed and the pressure in the flask was 2 atm.


(ii) Calculate the value of Kc, with units.

4. This question concerns the equilibrium
2NO(g)arrow N2(g) + O2(g) DH = –180 kJ mol–1

(ii) At 1600 °C and 1.5 atm pressure NO is 99 % dissociated at equilibrium. Calculate the value of Kp under these conditions.
(edited 10 years ago)
Original post by geor
It's definitely C. If you don't trust me then look at the old mark schemes, in one paper there's a question where you have to state why biofuels aren't carbon neutral, and the use of fertilisers and pesticides are both an answer.


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Doesn't burning biofuel produce CO2? :confused:
I marked C though. Since you're saying it's correct, I guess I got 1 marked saved there which means I will get 19/20 in Section A. :cool:
Original post by airheadbuster
Doesn't burning biofuel produce CO2? :confused:
I marked C though. Since you're saying it's correct, I guess I got 1 marked saved there which means I will get 19/20 in Section A. :cool:


This has nothing to do with the definition of 'carbon neutral'.
Reply 1731
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Original post by ALevel96
You're just stating functional groups instead of specifically stating the absorption spectrum that would occur


Yes, that was implied by the question and so none of the marks would be allocated for repeating it? evidently I wrote that the way you identify if those groups are present is by looking for the absorption patterns for each bond in the IR absorption spectra for both the product and molecule... The marks will be for mentioning the groups specific to each molecule and how therefore you can use the analysis to distinguish if the alcohol had been oxidised
This was a retake for me but the exam was okay. Lost about 5 marks. Still not too sure about the colour change in the titration :s-smilie:
Original post by geor
Energy released has nothing to do with CO2 released. And snap :smile:


Pg 238. Chemistry AS textbook. Please read the section "Carbon Neutrality".
Original post by geor
Me neither, what did you put? I put brown to colourless but now I realise it's probably pale yellow and I can see my answer in the reject column...


Yellow to colorless or red brown to colorless. Either will be accepted.
Original post by airheadbuster
Pg 238. Chemistry AS textbook. Please read the section "Carbon Neutrality".


Energy released is not considered when calculating carbon footprint. And yes, you are right that burning bioethanol does release CO2, this is counterbalanced by the fact that all the CO2 that is released had been absorbed by the plants and stored.
Reply 1736
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misty00
WHY would you stress yourselves out like this :/

Might aswell join in...

I think I messed up in the calculation page cos I used the molar mass of sn02 great :/

Also how did everyone find it generally? does anyone know what the grade boundries are or might be...they might be high cos everyone seems to have found it okay. The people I did it with really didn't like it
Don't have a camera in front of me now. So, I will quote the first paragraph only:

"A fuel is carbon neutral if the amount of carbon dioxide absorbed when the raw material grown, or the fuel is formed, equals the amount of carbon dioxide is produced when it is manufactured and then burned. For example, when a tree grows it absorbs carbon dioxide from the atmosphere. When the tree is burned it releases the same amount of carbon dioxide as it absorbed. So this process is carbon neutral. They do act as carbon reservoirs and if all the carbon stored in fossil fuels is released through burning it will have a major impact on the environment."
Reply 1738
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HKhan12
wat do we think the grade boundaries are going to be like?
Original post by geor
That doesn't prove your point haha! Energy released is not the same thing as amount of fuel burned AT ALL.


How exactly do you calculate energy released then? :confused:

Delta H = (Energy released when bonds are made) - (Energy required to break bonds)

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