Edexcel A2 Chemistry: CH04 (09/06/14) and CH05 (17/06/14) Watch

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LeaX
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Thought I would make a thread for all of us sitting these exams in June.

Specification: http://www.edexcel.com/migrationdocu...em_Issue_5.pdf

Link to past papers, mark schemes and examiner reports: http://www.edexcel.com/quals/gce/gce...s/default.aspx

Data booklet: here

Sample Paper and mark scheme: here

Practice paper: Edexcel-Chemistry-Practice-Test-Unit4 Mark scheme, starts on page 62

CH04 Notes by Peteyology: found here

Revision guide posted by mariagoretti : here
How's everyone's revision going?
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Peteyology
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anybody know how to do arrenhius plot? I've seen multiple exam questions worth a lot of marks for it!
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LeaX
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(Original post by Peteyology)
anybody know how to do arrenhius plot? I've seen multiple exam questions worth a lot of marks for it!
Are you referring to plotting lnk against 1/T to calculate the activation energy using the Arrhenius equation?
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Peteyology
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(Original post by LeaX)
Are you referring to plotting lnk against 1/T to calculate the activation energy using the Arrhenius equation?
yep, any ideas :confused:
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LeaX
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(Original post by Peteyology)
yep, any ideas :confused:
Well you'll always be given Arrhenius' equation as well as the value for R (8.31) so don't worry about that.
From what I've seen if it comes up (which I doubt it will as it came up June 2013), we'll be given data for k and T and potentially lnK and 1/T but we may have to work these out ourselves. Then you need to plot lnk against 1/T onto a graph using an appropriate scale (the graph has to cover at least half of the paper).

Once your points are drawn you need to calculate a line of best fit and then calculate the gradient. To calculate the gradient it's change in the y axis (which will be lnk) over change in the x axis (1/T).

The gradient = lnk/(1/T)
If we rearrange Arrhenius equation: lnk = -Ea/R x 1/T + constant
lnk/(1/T) = -Ea/R
Therefore lnk/(1/T) x R = -Ea
So our gradient x R = -Ea
gradient x 8.31 = -activation energy

Does this help? If so please let me know which aspect you're having trouble with and I'll try and explain it clearer or find some good resources.
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Peteyology
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(Original post by LeaX)
Well you'll always be given Arrhenius' equation as well as the value for R (8.31) so don't worry about that.
From what I've seen if it comes up (which I doubt it will as it came up June 2013), we'll be given data for k and T and potentially lnK and 1/T but we may have to work these out ourselves. Then you need to plot lnk against 1/T onto a graph using an appropriate scale (the graph has to cover at least half of the paper).

Once your points are drawn you need to calculate a line of best fit and then calculate the gradient. To calculate the gradient it's change in the y axis (which will be lnk) over change in the x axis (1/T).

The gradient = lnk/(1/T)
If we rearrange Arrhenius equation: lnk = -Ea/R x 1/T + constant
lnk/(1/T) = -Ea/R
Therefore lnk/(1/T) x R = -Ea
So our gradient x R = -Ea
gradient x 8.31 = -activation energy

Does this help? If so please let me know which aspect you're having trouble with and I'll try and explain it clearer or find some good resources.
No that helped a lot, I am just bad at rearranging the equations. To work out 1/T and lnK we will be given T and K etc. in a table though?

Thanks!
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LeaX
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(Original post by Peteyology)
No that helped a lot, I am just bad at rearranging the equations. To work out 1/T and lnK we will be given T and K etc. in a table though?

Thanks!
From what I've seen of previous questions, yep we'll be given T and k.
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saifulahmed
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1.Apply a knowledge of the rate equations for the hydrolysis of
halogenoalkanes to deduce the mechanisms for primary and
tertiary halogenoalkane hydrolysis and to deduce the mechanism
for the reaction between propanone and iodine

2. Demonstrate that the mechanisms proposed for the hydrolysis
of halogenoalkanes are consistent with the experimentally
determined orders of reactions, and that a proposed mechanism
for the reaction between propanone and iodine is consistent with
the data from the experiment in 4.3e.

can someone help me on these four topics?i cant find or understand anything on these!:/
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LeaX
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(Original post by saifulahmed)
1.Apply a knowledge of the rate equations for the hydrolysis of
halogenoalkanes to deduce the mechanisms for primary and
tertiary halogenoalkane hydrolysis and to deduce the mechanism
for the reaction between propanone and iodine

2. Demonstrate that the mechanisms proposed for the hydrolysis
of halogenoalkanes are consistent with the experimentally
determined orders of reactions, and that a proposed mechanism
for the reaction between propanone and iodine is consistent with
the data from the experiment in 4.3e.

can someone help me on these four topics?i cant find or understand anything on these!:/
1. Does it give you the rate equations? Tertiary halogenoalkanes always undergo SN1 because of steric hinderance. SN1 means there's only one reactant in the rate-determining step so we can deduce the mechanism from this. The C-Hal bond will break (which is the slow/rate-determining step), forming a carbocation intermediate. Then the second step (which is fast so it doesn't determine the rate of reaction) occurs where the OH- nucleophile attacks the C+.
Primary halogenoalkanes, however, undergo SN2. Because they're less bulky they can form a transition state where a Carbon temporarily has five bonds. The first step involves both the halogenoalkane and the OH- nucleophile.

To summarise:
- Primary halogenoalkanes: SN2, so both reactants in the rate-determining step and therefore in the rate equation.
- Tertiary: SN1. Only the halogenoalkane is in the rate-determing step and rate equation.

I recommend reading this page: here

Let me know if you're still confused and I'll try and explain it clearer.
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saifulahmed
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Is there any thread for unit 5?
if there is not one can someone please explain me this-
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why Eo cell is not 1.33-0.41?
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LeaX
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(Original post by saifulahmed)
Is there any thread for unit 5?
if there is not one can someone please explain me this-
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Size:  23.2 KB
why Eo cell is not 1.33-0.41?
I don't think there is a unit 5 thread. I haven't done unit 5 since last year so excuse me if I'm bad at explaining.

Because in the full equation you're going from Cr3+ to Cr2O72- you need to reverse the equation (and hence the Ecell value) for Cr3+. So +1.33 becomes -1.33.
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saifulahmed
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(Original post by LeaX)
I don't think there is a unit 5 thread. I haven't done unit 5 since last year so excuse me if I'm bad at explaining.

Because in the full equation you're going from Cr3+ to Cr2O72- you need to reverse the equation (and hence the Ecell value) for Cr3+. So +1.33 becomes -1.33.
yah i got it!!i wrote the reverse eqn and wrote +1.33 V but it is supposed to be -1.33V! thanx!and aren't you sitting for any exam this june?
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LeaX
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(Original post by saifulahmed)
yah i got it!!i wrote the reverse eqn and wrote +1.33 V but it is supposed to be -1.33V! thanx!and aren't you sitting for any exam this june?
and I'm just sitting CH04 as a resit.
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Peteyology
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I've managed to compile every single question paper and make notes on everything that has come up since 2009; arranged into topics this should be easy to study from and get an idea of where you are/aren't picking up marks on each question.

There seems to be a repeat of most questions on every paper. Entropy and acid (buffer or titrations) calculations have come up on every single paper. Also the HCN mechanisms are used a lot for rate along with the iodine titration.

I will do the same for Unit 5 soon:cool:
Attached files
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LeaX
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(Original post by Peteyology)
I've managed to compile every single question paper and make notes on everything that has come up since 2009; arranged into topics this should be easy to study from and get an idea of where you are/aren't picking up marks on each question.

There seems to be a repeat of most questions on every paper. Entropy and acid (buffer or titrations) calculations have come up on every single paper. Also the HCN mechanisms are used a lot for rate along with the iodine titration.

I will do the same for Unit 5 soon:cool:
Wow this is amazing! Thank you for posting.
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Peteyology
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(Original post by LeaX)
Wow this is amazing! Thank you for posting.
No problem, makes the exam look easy now! :rolleyes:
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mariagoretti
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(Original post by Peteyology)
I've managed to compile every single question paper and make notes on everything that has come up since 2009; arranged into topics this should be easy to study from and get an idea of where you are/aren't picking up marks on each question.

There seems to be a repeat of most questions on every paper. Entropy and acid (buffer or titrations) calculations have come up on every single paper. Also the HCN mechanisms are used a lot for rate along with the iodine titration.

I will do the same for Unit 5 soon:cool:
You're a lifesaver!

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Peteyology
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Forgot to mention I did not include organic reactions, like the questions that ask for what is the product or what reactants/conditions are used. These are easily learnt and better learnt using a flow diagram type of thing
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LeaX
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I found these practice questions online and they're pretty helpful. The questions are a little more challenging than the real exam paper (in my opinion anyway) so they're good practice.

Edexcel-Chemistry-Practice-Test-Unit4
Mark scheme, starts on page 62
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Peteyology
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How's study going? Not many people seem to be doing edexcel o.o maybe they haven't realised the exams soon!! Does someone want to create a unit 5 thread that will keep an eye on it; I will be done with unit 5 notes this week comming if anybody wants them!
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