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

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Original post by wilsea05
2.8g of brass, all the stuff before step 4 was irrelevant tbh.
the equation for copper and KI is
2Cu2+ 4I- -> 2CuI + I2

then that was titrated against sodium thiosulphate with the eqation
2S2O32- + I2 -> S4O62- + 2I-

so 2 moles of thiosulphate = 2 moles of copper
0.0298x0.1= moles of thiosulphate = moles of Cu2+
=0.0029x10 = moles in the 250cm3, x 63.5 = 1.8923g/2.8x100 = 67.58...%
answer asked for one decimal place so its 67.6%


You just made everything make more sense and explained why my answer was two times too small :smile:

Nonetheless, should we have been able to figure out the equation for Cu and KI, or was it a synoptic thing?
Reply 3101
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bino756
Original post by 93M


the 9 markers weren't too bad. (I forgot to x10 on the last calculation so did it for the 25cm instead of 250cm) It was the buffers question that threw me. Overall, I thought it was a pretty good paper as it covered the spec thoroughly and had good distribution of hard and easier marks. I don't know if that will translate into my marks or not as it was quite difficult but I am not at all annoyed about this paper. Bio and D1 maths are a different story for me though.
Reply 3102
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bino756
Original post by Ja-m-ie
You just made everything make more sense and explained why my answer was two times too small :smile:

Nonetheless, should we have been able to figure out the equation for Cu and KI, or was it a synoptic thing?


It was in the book
Anything above 105ums will do me nicely! God why did they have to make this paper on OUR year?
ok i need some reassurance here....my f***ing teacher told me today that he thinks the grade boundaries are gonna be 80 raw for 120 ums....please say this is completely wrong...tbf he said jans f324 was easy (and it wasnt) :frown::frown::frown:
Original post by bambinooo
ok i need some reassurance here....my f***ing teacher told me today that he thinks the grade boundaries are gonna be 80 raw for 120 ums....please say this is completely wrong...tbf he said jans f324 was easy (and it wasnt) :frown::frown::frown:


I'd be gob smacked if the grade boundaries were that high after all the hype.
Reply 3106
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gradu
8
I found the Jan 2011 easy.

This was rock hard.
Reply 3107
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Nbear
5
Original post by bambinooo
ok i need some reassurance here....my f***ing teacher told me today that he thinks the grade boundaries are gonna be 80 raw for 120 ums....please say this is completely wrong...tbf he said jans f324 was easy (and it wasnt) :frown::frown::frown:


he is definitely wrong, the paper we did was similar to the jan 11 paper, so the grade boundaries should be similar ...

also someone earlier in the thread said that their teacher used to be an ocr examiner, and they said that the paper was hard, so tbh id be more inclined to believe them than any other teacher
emailed ofqual...turd response...some regulators they are.....'oh we need the response from you teacher or your examining body'



yeah right, like OCR are going to email them admitting they fooked up!!!
(edited 12 years ago)
Reply 3109
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93M
10
Original post by viksta1000
emailed ofqual...turd response...some regulators they are.....'oh we need the response from you teacher or your examining body'



yeah right, like OCR are going to email them admitting they fooked up!!!


"fooked up" ? oh yeah, apart from the longer 9 markers and the time limit, it was an alright exam, everything was on the spec. it's your own fault if you didn't learn it properly or didn't do enough past paper questions
Original post by 93M
"fooked up" ? oh yeah, apart from the longer 9 markers and the time limit, it was an alright exam, everything was on the spec. it's your own fault if you didn't learn it properly or didn't do enough past paper questions


Ok, tbf i actually agree with u with the fact it covered most topics

But where on the syllabus does it teach you to apply chemistry in the way they applied it in the exam paper?

E.g negative enthalpy change of solution? Recharging cells? Buffer ratios?

Theres not a single question, spread, paragraph or even a sentence that teaches you to apply these topics in the way they asked in the exam

Its not long before you add up the marks for these sort of question and find youve lost 20+ marks
(edited 12 years ago)
Original post by viksta1000
Ok, tbf i actually agree with u with the fact it covered most topics

But where on the syllabus does it teach you to apply chemistry in the way they applied it in the exam paper?

E.g negative enthalpy change of solution? Recharging cells? Buffer ratios?

Theres not a single question, spread, paragraph or even a sentence that teaches you to apply these topics in the way they asked in the exam

Its not long before you add up the marks for these sort of question and find youve lost 20+ marks


Negative enthalpy change of solution was in my textbook, so was the cell recharge thing. But not the buffer ratios.

Tbh looking back at the paper, it wasn't bad overall, it was just those fat ass questions. The magic tang one and the one at the end were uncalled for, as well as the polymer of the complex ion. But other than that it wasn't too bad, and those bad questions take up only about 15-20marks.

Grade boundary in Jan was 59 for an A wasn't it. So even if you didn't answer those horrid questions, you could still be well in for an A, according to Januarys boundaries.
Original post by BackDoorEntry
Negative enthalpy change of solution was in my textbook, so was the cell recharge thing. But not the buffer ratios.

Tbh looking back at the paper, it wasn't bad overall, it was just those fat ass questions. The magic tang one and the one at the end were uncalled for, as well as the polymer of the complex ion. But other than that it wasn't too bad, and those bad questions take up only about 15-20marks.

Grade boundary in Jan was 59 for an A wasn't it. So even if you didn't answer those horrid questions, you could still be well in for an A, according to Januarys boundaries.


well looking at the OCR book I can't see negative enthalpy change of solution, it just says it can be exothermic or endothermic....but there's no application of an exothermic enthalpy change of solution...unless you can direct me to a page?

yes, the magic tang, the ionic equation ones were the ones that stumped me, although I did attempt them....got 33% for the ionic one which was half of the answer, so should hopefully get some method marks

I think if grade boundaries are similar to that of Jan 11 (65) then it wasn't too bad...although I don't see OCR lowering them more than that even though Jan 11 was IMO easier than June 11
Original post by viksta1000
well looking at the OCR book I can't see negative enthalpy change of solution, it just says it can be exothermic or endothermic....but there's no application of an exothermic enthalpy change of solution...unless you can direct me to a page?

yes, the magic tang, the ionic equation ones were the ones that stumped me, although I did attempt them....got 33% for the ionic one which was half of the answer, so should hopefully get some method marks

I think if grade boundaries are similar to that of Jan 11 (65) then it wasn't too bad...although I don't see OCR lowering them more than that even though Jan 11 was IMO easier than June 11


Which OCR book do you have?

I got 3.3% (doh) :frown: I knew it was wrong but didn't have any time to correct it!

Yeah that gives a huge 35 mark cushion before you drop down below 120UMS, which is actually quite generous. The only problem is a good percentage of people will have lost around 20 marks straight off!

But yeah which OCR book do you have?
Original post by BackDoorEntry
Which OCR book do you have?

I got 3.3% (doh) :frown: I knew it was wrong but didn't have any time to correct it!

Yeah that gives a huge 35 mark cushion before you drop down below 120UMS, which is actually quite generous. The only problem is a good percentage of people will have lost around 20 marks straight off!

But yeah which OCR book do you have?


The OCR Heinemman with the blueish blackish cover with 'Chemistry' written in Orange and its got a picture of some sort of cell dividing :confused:
Reply 3115
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93M
10
Original post by viksta1000
Ok, tbf i actually agree with u with the fact it covered most topics

But where on the syllabus does it teach you to apply chemistry in the way they applied it in the exam paper?

E.g negative enthalpy change of solution? Recharging cells? Buffer ratios?

Theres not a single question, spread, paragraph or even a sentence that teaches you to apply these topics in the way they asked in the exam

Its not long before you add up the marks for these sort of question and find youve lost 20+ marks


Fair point, but on the specification it does say "Candidates are expected to apply knowledge, understanding and other skills gained in this unit to
new situations and/or to solve related problems" for both AS and A2 and it also mentions "AO2 Application of Knowledge and Understanding" which includes "apply scientific knowledge and processes to unfamiliar situations"

http://www.ocr.org.uk/download/kd/ocr_9910_kd_gce_spec.pdf

I agree that application of knowledge to unfamiliar situations shouldn't make up a large part of the paper (as it did on this one unfortunately) but it is there in the specification.

The textbook should definitely include more examples of application of knowledge though.
Original post by viksta1000
The OCR Heinemman with the blueish blackish cover with 'Chemistry' written in Orange and its got a picture of some sort of cell dividing :confused:


pg174.

Underneath the title 'Breakdown of the ionic lattice'
Original post by 93M
Fair point, but on the specification it does say "Candidates are expected to apply knowledge, understanding and other skills gained in this unit to
new situations and/or to solve related problems" for both AS and A2 and it also mentions "AO2 Application of Knowledge and Understanding" which includes "apply scientific knowledge and processes to unfamiliar situations"

http://www.ocr.org.uk/download/kd/ocr_9910_kd_gce_spec.pdf

I agree that application of knowledge to unfamiliar situations shouldn't make up a large part of the paper (as it did on this one unfortunately) but it is there in the specification.

The textbook should definitely include more examples of application of knowledge though.


true, but even if they threw just one example in the book, just to give me a heads up, then I wouldn't be bothered

my main concern was that the paper was predominantly application/stretch and challenge, rather than just a couple of questions

we'll have to wait until august I guess...hopefully OCR haven't sabotaged my university chances
Original post by BackDoorEntry
pg174.

Underneath the title 'Breakdown of the ionic lattice'


that's just breaking an ionic lattice...that's going to be endo as it involves bond breaking

nothing about enthalpy change of solution :confused:

the only examples I can see are the ones on page 174-176 in which the enthalpy change of solution are endothermic
Original post by viksta1000
that's just breaking an ionic lattice...that's going to be endo as it involves bond breaking

nothing about enthalpy change of solution :confused:

the only examples I can see are the ones on page 174-176 in which the enthalpy change of solution are endothermic


In the exam it asked us for something, and all the arrows were pointing downwards. So you had to reverse the enthalpy change of solution so its arrow was pointing upwards I think, I can't remember the paper.

But yeah everything below 'Breakdown of the ionic lattice' and the next page kinda suggests the relationship between all three enthalpy changes, so in the exam they were asking you to apply this.

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