The Student Room Group

AQA CHEM 2 UNOFFICIAL Mark Scheme

I said I would give this ago. I by no means got all the questions right, I will check some things in textbooks but I can only guess at some of the answers, please let me know if you disagree with anything that I put.

Scroll to see replies

I've scanned the paper, the file was to large to attach but you can view it on my skydrive :smile:
https://skydrive.live.com/?cid=518dbdd4f043877a#cid=518DBDD4F043877A&id=518DBDD4F043877A%21187
(edited 12 years ago)
Answers

Question 1

a) (i) SiO2 + 2C + 2Cl2 > SiCl4 + 2CO
a) (ii) Distilled
b) (i) SiCl4 + 2H2 > Si 4HCL
b) (ii) Reducing agent
b) (iii) Explosion as hydrogen gas is flammable
c) 2MgO + Si > 2Mg + SiO2

Question 2

a) The forwards reaction is equal to the backwards/reverse reaction
Macroscopic properties do not change with time (i.e concentration of substances/colour/pressure)

b) A catalyst lowers the activation energy of a reaction by providing an alternative pathway, therefore it effects the forwards and reverse reaction equally, but has no effect on the position of equilibrium.

c) (i) Increases
Equilibrium has been disturbed and will move in a direction to oppose the disturbance. The equilibrium will shift left (to the side with the fewest moles of gas)

(ii) Decreases
Equilibrium has been disturbed and will move in a direction to oppose the disturbance. The reaction is exothermic and the position of equilibrium will shift left.

d) (i) A higher temperature increases the rate of the reaction
(ii) It is too expensive to maintain a high pressure.

Question 3

a) The fraction of particles with Energy, E
b) No effect
c) X
d) The two different particles must collide and must do so with sufficient energy (Energy greater than or equal to activation energy)
e) The particles have more kinetic energy, they move around faster and are more likely to collide and result in a reaction.

Question 4

a) (i) Reduction
(ii) Fe3+ +3e- > Fe3
b) (i) The reactants have an enthalpy value of zero
(ii) The enthalpy change of a reaction is the same regardless of the route taken from the reactants tot he products
(iii) The enthalpy change when one mole of compound is burnt completely in excess oxygen, under standard conditions. With all reactants and products in their standard states.
c) +1KJmol-1
d) (i) C(s,graphite) + 2O2 > CO2
(ii) Both form carbon dioxide.

Question 5

a) (i) 0
(ii) +5
b) IO3- + 5I- +6H+ > 3H2O +3I2
iodine?
c) (i) I2
(ii) (SO4)2- + 6e- + 8H+ > S + 4H2O
d) Hydrogen Sulphide
e) (i) I- + Ag+ > AgI
(ii) Nothing
(iii) To remove ions that would interfere with the test
f) (i) An electron donor
(ii) Cl2 + 2e- > 2Cl-
(iii) Iodide is a larger ion, it's outer shell of electrons is further from the nucleus therefore not as effected by the positive charge of the nucleus. Therefore it loses it's outer electrons more easily, making it a stronger reducing agent.

Question 6
a) Compounds 1 and 3 have the exact same elements, even when measuring to five decimal places their Mr will be exactly the same. The Mr of compounds 1 and 2 to five decimal places would be different as compound one contains an oxygen molecule and compound 2 does not.
b)
Fehling's
Compound 1: Brick red precipitate
Compound 2: No reaction
or
Tollens'
Compound 1: Silver mirror forms
Compound 2: No reaction

Question 7

a) (i) Increases
(ii) Decreases
(iii) Increases
b) The 'sea' of delocalised electrons gets further away from the nucleus as you go down the group, therefore the metallic bond becomes weaker and the melting points decrease slightly down the group.
c) (i) Sulphuric acid contains sulphate ions which would always produce a positive result.
(ii) BrCl+ + (SO4)2- > BaSO4 + Cl+

Question 8

a) Positional isomerism
b)
c)

Question 9

a) C6H12O6 > 2C2H5OH + 2CO2
Fermentation
C2H5OH + 3O2 > 2CO2 + 3H2O
For a process to be deemed carbon-netural the net production of carbon dioxide must be zero. Fermentation is carbon natural as the the carbon diode released is balanced by that as robed from the plant. The combustion of ethanol is not carbon neutral as carbon dioxide is relaxed in to the atmosphere.
b) Nucleophilic Substitution

Potassium hydroxide is used as a reagent and if this contaminates the alcohol and it consumed it would cause ill health.
c) Phosphoric acid
Hydration
High pressure
Low temperature

Question 10
a) CADB
b) The addition of bromine water, which is a brown/orange colour. When added to a carbon-carbon double it decolourises. Therefore when added to cyclohexane there would be no change and when added to cyclohexene it would decolourise.
c) Acidified dicrhomate
Oxidation
Secondary
d) Free-radical substation
Initiation: Br-Br > 2Br.
Propagation: Br. + CH4 > CH3. + HBr
CH3. + HBr > Br. + CH4
Termination: CH3. + HBr. > CH3Br
Ultra-violet radiation
(edited 12 years ago)
Reply 3
Pretty good overall, although I think some of the answers are a little too specific. Could you send me the paper please? :smile: Would really appreciate it :h:
If the equilibriums are moving to the left, surely the yield is decreasing?
Reply 5
Original post by byebyebadman
If the equilibriums are moving to the left, surely the yield is decreasing?


You're right!
Reply 6
Thank you so much for this, it must have taken you some time, with exams to revise for!!!

Thanks again :smile:, is it possible to maybe take screenshots of the paper and upload it here, so that we can see how many marks we have lost, pleasssssse? :smile: :smile:
Reply 7
Thanks for putting this up. Have you got the paper then?
I try and upload the paper tomorrow :smile:

I do have the paper 1Platinum, I took a copy at the end of the exam.
Reply 9
Original post by Picture~Perfect
I try and upload the paper tomorrow :smile:

I do have the paper 1Platinum, I took a copy at the end of the exam.


Thanks mate! :smile: :colondollar:

Do you by anychance have a webcam, maybe you can take screenshots?
Original post by casio1
Thanks mate! :smile: :colondollar:

Do you by anychance have a webcam, maybe you can take screenshots?


I have a scanner so I'm hoping to scan it and upload it that way *fingers crossed* I figured I would write out the questions, so people can see them if I can't upload the paper.
Reply 11
Thanks for this :smile:
It would be good if you upload the paper :biggrin:
Reply 12
Original post by Picture~Perfect
I have a scanner so I'm hoping to scan it and upload it that way *fingers crossed* I figured I would write out the questions, so people can see them if I can't upload the paper.


No worries man :smile: thank you
Original post by Picture~Perfect
I try and upload the paper tomorrow :smile:

I do have the paper 1Platinum, I took a copy at the end of the exam.


Cheers, I didn't know you were allowed to take a copy.
Reply 14
thanks so much for this! +rep :smile:

also.. 4a)i) doesn't iron oxide undergo reduction?


Original post by 1platinum
Cheers, I didn't know you were allowed to take a copy.


I think it just depends on the school/college. some people get hold of it through their teachers etc.
Original post by Sheo
thanks so much for this! +rep :smile:

also.. 4a)i) doesn't iron oxide undergo reduction?


I put reduction when I did the exam, but it uses a reducing agent so doesn't that make it oxidation? I'm abit iffy on redox.
Reply 16
Original post by Picture~Perfect
I put reduction when I did the exam, but it uses a reducing agent so doesn't that make it oxidation? I'm abit iffy on redox.


but you've gotta remember it's reduction of iron oxide using carbon.
yeah carbon is a reducing agent so therefore an electron donor, it gives electrons to iron.

Fe3+ +3e- > Fe3

Iron gains 3e- therefore it has to be a reduction :smile:

also will you be posting up the next part? :smile: thanks again!
Original post by Sheo
but you've gotta remember it's reduction of iron oxide using carbon.
yeah carbon is a reducing agent so therefore an electron donor, it gives electrons to iron.

Fe3+ +3e- > Fe3

Iron gains 3e- therefore it has to be a reduction :smile:

also will you be posting up the next part? :smile: thanks again!

That does make sense.
I will probably do the rest tomorrow now, I had a 2hr Physics exam this morning, I'm feeling pretty exhausted.
Original post by Picture~Perfect
That does make sense.
I will probably do the rest tomorrow now, I had a 2hr Physics exam this morning, I'm feeling pretty exhausted.


Wow, great guy/girl. I'm pretty sure it was Increased then Reduced for question 2 though.
Reply 19
upload the paper please.

Quick Reply

Latest