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# Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch

1. (Original post by Vidja)
I got the third half life value as 215. The way I was taught maths, 210 is greater than 190, and 215 is greater than 200 so I figured it was increasing.

From the sounds of things though, the third value was closer to 200 than 210. I'm just venting at the amount of application marks, really.
The third value was 200
I went and talked to my chemistry teacher afterwards who is an examiner for OCR chemistry and he said that cause it was 190, 210, 200 then it would average as 200 so therefore be first order and a constant half life
2. (Original post by CoventryCity)
This is what I done

Lattice enthalpy was around -2700 wasn't it and the enthalpy of solution around -300?
-2700 - 300 + 750 = Hydration enthalpy
I can remember the exact values obviously but I think it was -1941, we shall see when someone uploads the paper
3. Sorry to do this, but can anyone please let me know what result they got for the copper percentage in brass?
4. (Original post by Rachel-92)
The third value was 200
I went and talked to my chemistry teacher afterwards who is an examiner for OCR chemistry and he said that cause it was 190, 210, 200 then it would average as 200 so therefore be first order and a constant half life
If they want to show an constant half life why not do it PROPERLY instead of doing averages!!!? goshh! so annoying....because most people would think that would be a second order no?
5. i thought it was typical of ocr to bring out a paper like this...they have been trying to move down the knowledge application route rather than just content learning for a while now...anyways the exam style suits some more than others.

did anyone use ethanoic acid in the buffer question btw and what was the ratio?
6. (Original post by OscarK123)
Sorry to do this, but can anyone please let me know what result they got for the copper percentage in brass?
67.6%
7. (Original post by Rickesh)
If they want to show an constant half life why not do it PROPERLY instead of doing averages!!!? goshh! so annoying....because most people would think that would be a second order no?
As I said earlier, I think the half-life would've increased significantly more than 10s.
8. (Original post by OscarK123)
Sorry to do this, but can anyone please let me know what result they got for the copper percentage in brass?
I got 33.8% but I think that's wrong
9. (Original post by sportycricketer)
67.8%
Wow, so I acutally got a mark in the whole paper!

Thanks
10. (Original post by Dpax2max)
Hi everyone as soon as this paper ended my chem teacher took us up to the comp lab- and we all wrote letter of complaint. I know you all think it doesnt work but it does ! I know and the OCR people even told us this year that they you like feeback it is hard for us to know how student found the examm- because they could have really studied hard but not achieved the grades, how much effort a student puts in cant really be determined by their grade" We appreciate any feedback as it could alter grade boundaries-

seriously. I'm not being a brat- I'm a regular B student and I needed a B in this

send to
[email protected] k
I agree, we shouldn't allow them to continue producing these sorts of ridiculous exams - they're often choked with unnecessary description about random events or fictitious people and the many of the actual questions are ambiguously worded - even if the process of solving them is not particularly complex. Hopefully enough people will complain and they'll recognise that they need to change the papers. It just seems illogical to set these fiendishly difficult exams with low grade boundaries - why not do normal papers with the good old 80% for an A rule?
11. (Original post by Vidja)
From the textbook:
"A first order reaction can easily be identified from a concentration time graph. a first order reaction has a constant half life"

The half lives were 190 then 210.

Nowhere in the specification does it say "Half life is constant except sometimes when it's almost constant. It's still first order then."

The half life was increasing. If the mark scheme only gives a mark for first order then that is ridiculous.
I put order 1 just because it was only a line of best fit, many points were not on the line
12. Are OCR trying to kill us ?!!?
13. So much harder than january, I ran out of time so didn't even get on to the last question. I think I got about 80 raw, is there an chance of that being an A*?
14. (Original post by Sternumator)
So much harder than january, I ran out of time so didn't even get on to the last question. I think I got about 80 raw, is there an chance of that being an A*?
Yes going on January paper that would be full UMS
15. does anyone know where we can get the paper from??
16. (Original post by Rickesh)
If they want to show an constant half life why not do it PROPERLY instead of doing averages!!!? goshh! so annoying....because most people would think that would be a second order no?
It's irritating, but I guess I should have drawn the third line correctly.

I hate questions that are designed in such a way that they're expecting people to get them wrong. It just doesn't seem fair.
17. (Original post by sportycricketer)
10^-pKa = Ka

Ka x HA = [H+]^2
Get the value of [H+]
Sub it into the pH formula and I'm almost sure that it said 2 dp for this qs

I think i completely ignored the ka/pKa part, and took the conc. to mean a strong acid and that it fully dissociates and then worked out the pH, if that makes sense .
18. (Original post by lenalouiseh)
I agree, we shouldn't allow them to continue producing these sorts of ridiculous exams - they're often choked with unnecessary description about random events or fictitious people and the many of the actual questions are ambiguously worded - even if the process of solving them is not particularly complex. Hopefully enough people will complain and they'll recognise that they need to change the papers. It just seems illogical to set these fiendishly difficult exams with low grade boundaries - why not do normal papers with the good old 80% for an A rule?
When you start decreasing the difficulty of the papers and increasing the grade boundaries you can get situations where a few silly, generally unavoidable mistakes can cost you a grade. I'm of the opinion that exams should challenge on content rather than grade boundaries. That being said, the current curriculum isn't very good at preparing people for this sort of challenging stuff.

That being said, all the rubbish about the 'magic tang' as well as the hydrogen economy and other things like that, they all need to go.
19. Is It me or was that F325 exam harder than what anyone expected?? :s
20. (Original post by OscarK123)
Sorry to do this, but can anyone please let me know what result they got for the copper percentage in brass?
67-ish or something...I have to confess, the molar ratio they didn't give you I just guessed, since 1:1 gave you 130-something %, and 67% sounds roughly right for the percentage of copper in brass - also, given the equation it just seemed unlikely to be 1:3, so that's what I went for in the end! I have to say, at my (super-selective, science specialist, grammar) school people REALLY struggled with this paper - especially the tangy sweets question which was just ridiculous - and our head of chemistry is going to formally complain that it was just so ridiculously hard. The problem is, if the grade boundaries are reduced by a lot, then it makes all the grades quite close together, which means that the difference between a B and an A could just be the random stuff you scribbled down whilst trying to work out a question - which obviously isn't fair, as it doesn't mean you understood it any more than someone who didn't scribble something down.

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