Edexcel Chemistry Unit 2 - 4 June 2013 Unofficial Mark scheme & paper
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Original post by geor
I think this is actually,
PCl5 + C4H9OH ===> C4H9Cl + HCl + POCL3 [2] (no state symbols required)
Also just a small reminder to people to take these mark scheme lightheartedly, it's stupid to calculate your exact mark because no one knows what is going to be in the mark scheme (we could be all wrong!) and sometimes they are stupidly picky.
PCl5 + C4H9OH ===> C4H9Cl + HCl + POCL3 [2] (no state symbols required)
Also just a small reminder to people to take these mark scheme lightheartedly, it's stupid to calculate your exact mark because no one knows what is going to be in the mark scheme (we could be all wrong!) and sometimes they are stupidly picky.
yeah thats right. There are a few other mistakes too but its nice to have something to compare with
but definitely the ''markscheme'' part needs a large pinch of salt
Original post by Al_Chemist
iii) Stretches bonds. [1]
iii) Stretches bonds. [1]
I think for this one, you should have said; 'There is a change in dipole moment' . This is the classic answer but that might also get it.
Original post by Al_Chemist
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region. [2]
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region. [2]
I disagree with this one.
As H+ ions are added to the equilibrium, the concentration on the right hand side increases. Therefore, equilibrium shifts to the left, thus increasing the concentration of bromine. But I am not 100% sure anyway...
Original post by Priya08
God hope their a few marks lower !! Think I got about 54/80
Messed up..made so many silly mistakes
Messed up..made so many silly mistakes
That will be a definite C
My predictions:
A-63
B-58
C-53
120 UMS 73/80
Original post by thephysicsguy
I disagree with this one.
As H+ ions are added to the equilibrium, the concentration on the right hand side increases. Therefore, equilibrium shifts to the left, thus increasing the concentration of bromine. But I am not 100% sure anyway...
As H+ ions are added to the equilibrium, the concentration on the right hand side increases. Therefore, equilibrium shifts to the left, thus increasing the concentration of bromine. But I am not 100% sure anyway...
Why would they increase on the right hand side?
Original post by Al_Chemist
Why would they increase on the right hand side?
Well you're adding acid which is a solution and there will be H+ (more truly hydronium) ions around. So these H+ can join the equilibrium hence increasing the concentration in RHS.
Original post by Al_Chemist
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region. [2]
This is wrong, the HCl dissociating into H+ and Cl- means the H+ conc. increases, shifting the equilibrium to the left to counter the change.
Original post by Al_Chemist
iii) Stretches bonds. [1]
This is right, but I think "change in polarity" will also be accepted.
Original post by Al_Chemist
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region.
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region.
Are you sure this was right? i thought that we needed to talk about equilibria since adding HCL pushes the equilibrium to the Br2 and H2O side so less bromine is hydrolyzed do you think they'll accept that as an answer?
Original post by mar junior
Are you sure this was right? i thought that we needed to talk about equilibria since adding HCL pushes the equilibrium to the Br2 and H2O side so less bromine is hydrolyzed do you think they'll accept that as an answer?
Original post by Maybenexttime
This is wrong, the HCl dissociating into H+ and Cl- means the H+ conc. increases, shifting the equilibrium to the left to counter the change.
So far myself, mar junior and Maybenexttime thinks that the hydrolisis equation question is to do with the H+ conc. increasing in RHS hence shifting equilibrium to left. So it has hopefully been approved.Btw guys don't comment on a thread before having a look at what has been written :P
Original post by Al_Chemist
Paper attached ; Credit to HarryMWilliams
1. D
2. B
3. C
4. A
5. C
6. A
7. C
8. A
9. B
10. D
11. D
12. B
13. B
14. C
15. A
16. B
17. D
18. A
19. C
20. C
Section A = 20
21.
a) i) Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g) [2]
ii) (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2) [2]
b) White solid – as BaSO4 is insoluble. [2]
c) Ba(OH)2 + 2HCl ===> BaCl2 + 2H2O [1] (no state symbols required)
d) i) MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
MgCO3(s)===>MgO(s) + CO2(g) (or equation for decomposition of BaCO3 : BaCO3===>BaO(s) + CO2(g) ) [2]
ii) Flame Test;
MgCO3 – no flame colour
BaCO3 – Apple-Green/Green flame colour [2]
22.
a) i) NaOH/Sodium hydroxide dissolved in ethanol. [1]
ii) Elimination [1]
iii)Aqueous NaOH/Sodium hydroxide [1]
iv) Suitable mechanism (Secondary alcohols usually undergo SN1 mechanism, but SN2, may also be accepted) [2]
b) Misty fumes (released)
PCl5 + C4H9OH ===> C4H9Cl + HCl + POCL3 [2] (no state symbols required)c) i) Orange to Green with Butan-2-ol, and no (colour) change with A. [2]
ii) CH3C(=O)CH2CH3 [1]
iii) Lack of absorption of -OH.[1]
23.
a) London Forces/any correct name eg Dispersion forces etc. [1]
b) 18 (electrons) [1]
c) CH3F has permanent dipoles (F2 does not) - permanent dipoles are stronger.[1]
d) HF can form hydrogen bonds (others in series cannot), Hydrogen bonds are the strongest (intermolecular) force, so requires more energy to separate HF molecules. [2]
e) Cl atom too large/Not electronegative enough, to form Hydrogen bonds. [1]
24.
a) i) 0.00116 [1]
ii) 0.00058 [1]
iii)0.0125[1]
iv) 0.01192[1]
v) 13.8% (3s.f.)[2]
b) i) Separate solutions to obtain more results. [1]
ii) Percentage error = 0.86% [1]
iii) Reducing thiosulfate concentration, thus increasing titration reading, hence percentage error decreases.[1]
c) Pale Yellow to colourless [1]
Section B = 38 marks
25.
a) i) 2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm [1]
ii) Cl2(g) + 2Br-(aq) ===> 2Cl-(aq) + Br2(g) [2]
iii) Brown colour [1]
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region. [2]
v) Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases. [2]
vi) More molecules have energy equal to or greater than the activation energy (so more successful collisions). [1]
vii) Br simultaneously reduced from 0 to -1 and oxidised from 0 to +1. [2]
b) i) Forward reaction=Backward reaction
No change in concentration [2]
ii)More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced. [2]
iii) Stretches bonds. [1]
iv) The molecules absorb IR re-re-radiating from Earth. [2]
v) Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide concentrations in the atmosphere more than water vapour. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increasing, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be caused by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations. [4]
Section C = 22 marks
Total marks [80]
I'd like to ask whoever negged me, to make a better mark scheme, if they dare.
1. D
2. B
3. C
4. A
5. C
6. A
7. C
8. A
9. B
10. D
11. D
12. B
13. B
14. C
15. A
16. B
17. D
18. A
19. C
20. C
Section A = 20
21.
a) i) Ba(s) + 2H2O(l) ==> Ba(OH)2(aq) +H2(g) [2]
ii) (Redox reaction) Ba increases in oxidation number from 0 to +2 and H changed from +1 to 0 (in H2) [2]
b) White solid – as BaSO4 is insoluble. [2]
c) Ba(OH)2 + 2HCl ===> BaCl2 + 2H2O [1] (no state symbols required)
d) i) MgCO3 decomposes more quickly than BaCO3, shown by limewater turning cloudy more quickly or gas produced more quickly
MgCO3(s)===>MgO(s) + CO2(g) (or equation for decomposition of BaCO3 : BaCO3===>BaO(s) + CO2(g) ) [2]
ii) Flame Test;
MgCO3 – no flame colour
BaCO3 – Apple-Green/Green flame colour [2]
22.
a) i) NaOH/Sodium hydroxide dissolved in ethanol. [1]
ii) Elimination [1]
iii)Aqueous NaOH/Sodium hydroxide [1]
iv) Suitable mechanism (Secondary alcohols usually undergo SN1 mechanism, but SN2, may also be accepted) [2]
b) Misty fumes (released)
PCl5 + C4H9OH ===> C4H9Cl + HCl + POCL3 [2] (no state symbols required)c) i) Orange to Green with Butan-2-ol, and no (colour) change with A. [2]
ii) CH3C(=O)CH2CH3 [1]
iii) Lack of absorption of -OH.[1]
23.
a) London Forces/any correct name eg Dispersion forces etc. [1]
b) 18 (electrons) [1]
c) CH3F has permanent dipoles (F2 does not) - permanent dipoles are stronger.[1]
d) HF can form hydrogen bonds (others in series cannot), Hydrogen bonds are the strongest (intermolecular) force, so requires more energy to separate HF molecules. [2]
e) Cl atom too large/Not electronegative enough, to form Hydrogen bonds. [1]
24.
a) i) 0.00116 [1]
ii) 0.00058 [1]
iii)0.0125[1]
iv) 0.01192[1]
v) 13.8% (3s.f.)[2]
b) i) Separate solutions to obtain more results. [1]
ii) Percentage error = 0.86% [1]
iii) Reducing thiosulfate concentration, thus increasing titration reading, hence percentage error decreases.[1]
c) Pale Yellow to colourless [1]
Section B = 38 marks
25.
a) i) 2,200ppm>60ppm, thus 2.2g dm^-3 is greater than 60ppm [1]
ii) Cl2(g) + 2Br-(aq) ===> 2Cl-(aq) + Br2(g) [2]
iii) Brown colour [1]
iv) HCl dissociates into H+ and Cl-, H+ reacts with OH- to form water, so nucleophile unable to attack electron deficient region. [2]
v) Increase in temperature favours the forward reaction (as endothermic), thus equilibrium position moves to the right, thus rate of hydrolysis increases. [2]
vi) More molecules have energy equal to or greater than the activation energy (so more successful collisions). [1]
vii) Br simultaneously reduced from 0 to -1 and oxidised from 0 to +1. [2]
b) i) Forward reaction=Backward reaction
No change in concentration [2]
ii)More carbonate ions, equilibrium position moves to the right to remove extra carbonate ions, thus less CO2 produced. [2]
iii) Stretches bonds. [1]
iv) The molecules absorb IR re-re-radiating from Earth. [2]
v) Scientists are more worried about Carbon Dioxide than water vapour as Carbon Dioxide concentrations in the atmosphere more than water vapour. Anthropogenic climate change is due to human activities eg burning of fossil fuels. Burning of fossil fuels is increasing, so levels of carbon dioxide in the atmosphere is likely to continue increasing. Natural climate change may be caused by natural processes such as the formation of carbonates in rocks that remove CO2 in longer durations. [4]
Section C = 22 marks
Total marks [80]
I'd like to ask whoever negged me, to make a better mark scheme, if they dare.
Surely Q6 is B? I've looked this up and it seems to be B but I would understand why it's A (a lot of the sources I found mentioned both points A and B as to why they didn't dissolve in petrol)
for question dii. would you still get marks if you talk about the solubility of the two different compounds rather than flame tests. I was thinking of putting a flame test but it said other than heating so I decided to go for solubility instead 
(edited 10 years ago)
Original post by ATemple96
Surely Q6 is B? I've looked this up and it seems to be B but I would understand why it's A (a lot of the sources I found mentioned both points A and B as to why they didn't dissolve in petrol)
It is B. This mark scheme has quite a few mistakes on it
Original post by Goods
It is B. This mark scheme has quite a few mistakes on it
Haha I hope so...I was completely stuck on that question so I just put the one I thought looked best ://
Original post by Maybenexttime
This is wrong, the HCl dissociating into H+ and Cl- means the H+ conc. increases, shifting the equilibrium to the left to counter the change.
This is right, but I think "change in polarity" will also be accepted.
This is right, but I think "change in polarity" will also be accepted.
Original post by ALevel96
That will be a definite C
My predictions:
A-63
B-58
C-53
120 UMS 73/80
My predictions:
A-63
B-58
C-53
120 UMS 73/80
Original post by Al_Chemist
Why would they increase on the right hand side?
I WROTE BONDS VIBRATE ..... can it be accepted??
Original post by Goods
yeah thats right. There are a few other mistakes too but its nice to have something to compare with but definitely the ''markscheme'' part needs a large pinch of salt
but definitely the ''markscheme'' part needs a large pinch of saltPlease can you check my answer in the previous post?
Original post by Daniel Atieh
Please can you check my answer in the previous post?
the bonds vibrate would get the marks if you mentioned that they were also polar i think, but on its own i doubt it..
The point is that as the bonds vibrate they cause a shift in the dipole and then IR radiation can then be absorbed by the bonds as the vibrate.
Original post by Goods
the bonds vibrate would get the marks if you mentioned that they were also polar i think, but on its own i doubt it..
The point is that as the bonds vibrate they cause a shift in the dipole and then IR radiation can then be absorbed by the bonds as the vibrate.
The point is that as the bonds vibrate they cause a shift in the dipole and then IR radiation can then be absorbed by the bonds as the vibrate.
yea, so theres a chance right?
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