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# ocr a f325 revision thread watch

1. (Original post by Better)
Hahah glad someone gets the reference!!! We have someone who lifts on this Forum!
Just out of curiosity have you tried any of the questions yet? Sorry about my annotations on the questions as that helps me break it down into the trivial steps

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2. I've just marked Q5a(ii) from jan 2012 paper and thought it to be straightforward but i have got my sign for Ni electrode wrong way round and don't understand why. I assumed that in Cell A the more positive electrode is the iron system so that gets reduced and will have negative sign so nickel will have positive.

(Sorry I haven't got electronic copy because I'm on phone!)

Thanks!
3. (Original post by Myda)
I've just marked Q5a(ii) from jan 2012 paper and thought it to be straightforward but i have got my sign for Ni electrode wrong way round and don't understand why. I assumed that in Cell A the more positive electrode is the iron system so that gets reduced and will have negative sign so nickel will have positive.

(Sorry I haven't got electronic copy because I'm on phone!)

Thanks!
for Q5a) ii.. Cell A is based on redox system 1 and 2.. in order to determine the sign of the Ni electrode, u have to look at the electrode potentials.. Ni is -0.25 and Fe is 0.77.. so, the more negative electrode is oxidised, so, Ni has to be negative because it loses electrons.. Fe3+ is reduced as it gains the electrons.. simple mark.. just think about it.. it is pretty straightforward
4. (Original post by MedMed12)
anyone know what the highest an A has been and an A*?
84% = A* jan 12
5. (Original post by MathsNerd1)
Here are the questions, I hope they are big enough to read.

Attachment 222661 Attachment 222662 Attachment 222663 Attachment 222664 Attachment 222665

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Do you have answers to them?
6. (Original post by Dr00n)
Do you have answers to them?
Oh yeah, I forgot to post them, sorry.

Here they are
Spoiler:
Show

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7. (Original post by MedMed12)
I've just posted the answers to those questions I posted earlier

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8. are we supposed to know that HNO3 is an oxidising agent, because it makes sense but knowledge of it is news to me and we're a weekish away from the exam
9. (Original post by Dr00n)
are we supposed to know that HNO3 is an oxidising agent, because it makes sense but knowledge of it is news to me and we're a weekish away from the exam
Don't think so!
10. Hi guys, I was wondering if someone could help me work out how to label conjugate acid-base pairs? I can't tell how you work out which one is A1 or B1 and why it matters the order of B1 and B2 etc. Hope that question made sense thank you!
11. (Original post by MathsNerd1)
Yeah, I'll post them when I get home tonight

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thank you
(Original post by master y)
84% = A* jan 12

Thanks just hoping its not like the Jan paper tbh although overall it wasnt that bad, just nothing like before.

(Original post by gingerninja22)
Hi guys, I was wondering if someone could help me work out how to label conjugate acid-base pairs? I can't tell how you work out which one is A1 or B1 and why it matters the order of B1 and B2 etc. Hope that question made sense thank you!

you can label the pairs either way round-doesn't matter which one is A or B but to work out what pairs with what, look at what is happening for example

CH3C00H +H20 ---> CH3COO- and H30+

CH3COOH has lost a proton -so it is a acid (acids are proton donors) and CH3COO- must therefore be a base- you can label that pair 1
H20 ---> gains a proton so is an acceptor (bases are proton acceptors) so is a base making H30+ an acid

hope this helps
12. (Original post by Dr00n)
are we supposed to know that HNO3 is an oxidising agent, because it makes sense but knowledge of it is news to me and we're a weekish away from the exam
im sure they'd give it on context where you could work it out?
13. (Original post by zef1995)
I agree, it was a challenging paper! You're welcome, I'm glad that I can help!
I'm guessing you've just done Jan 13 as a mock? You may have done better than you think! At least we have a difficult paper as a mock, it means we can see the type of stretch and challenge questions they can ask and learn how to tackle them
I hope your revision is going well!
I agree

(Original post by Better)
Just marked my Paper, here is my score Breakdown:

Total Score 77/100
Q1: 11/13
Two Elements that have atoms with two unpaired d electrons - Not so sure

Q2 - 10/11

Q3 - 15/16 - small error

Q4 5/10

Not sure about How to determine the initial rate?
I think I understand part c now.

Q5 - 7/10

ARGH, I tried to jump steps on the Equilibrium question, probably best to write things down explicitly

Q6 - 14/14

Q7 - 13/16
- Not sure about the full Ionic equation of Q7bii - Ca(HS03)2 OXIDISES Magnesium.. I think because there were two metals I was confused, could anyone explain this part?
- Got the Reaction of the Base wrong too.
- Question 7cii - Possible Equation - Got that wong apparently it was Benzoic Acid
- The last bit - I thought the rate of dissociation would be too slow so it would make a difference which apparently was wrong.

Q8- 2/10 :O :O :O
NOT sure whats going on :/ :/

If that was the Jan paper then well done you!!
14. (Original post by MedMed12)

you can label the pairs either way round-doesn't matter which one is A or B but to work out what pairs with what, look at what is happening for example

CH3C00H +H20 ---> CH3COO- and H30+

CH3COOH has lost a proton -so it is a acid (acids are proton donors) and CH3COO- must therefore be a base- you can label that pair 1
H20 ---> gains a proton so is an acceptor (bases are proton acceptors) so is a base making H30+ an acid

hope this helps
Thank you so much, yes it did!
15. (Original post by Better)
Just marked my Paper, here is my score Breakdown:

Total Score 77/100
Q1: 11/13
Two Elements that have atoms with two unpaired d electrons - Not so sure

It wants just two unpaired d electrons. Electron configurations work by having orbitals in pairs, but first each energy level is filled with one electron. So, as the EC of a transition metal is always (first row ones!) [Ar]4s2 (or 1 if copper/chromium) then look for the two with 2 orbitals with 1 electrons. This will be
Spoiler:
Show
Nickel [Ar]4s23d8 and Titanium [Ar]4s23d2. Although Nickel has 8 electrons in it's d-subshell, this means that 3 orbitals are completely filled, and so the other two must only be half filled - or unpaired
. Hope that makes sense

Q2 - 10/11

Q3 - 15/16 - small error

Q4 5/10

Not sure about How to determine the initial rate?
I think I understand part c now.

Clock reactions etc, so a sudden change. You would add a
Spoiler:
Show
starch solution to the solution forming Iodine as it then goes a dark blue colour. You can then do the disappearing cross experiment, measure the time, and then do 1/t to get the rate. So, the time take, is the rate, which you can assume to be the initial rate. You should then vary the [I-] and [S2O8(?)-] whilst keeping the other constant. Then by doing say 5 of these clock reactions for each, you'd have enough results to plot an initial rate/conc graph. A straight, linear line (y=x) through the origin, will show that the reactant is first order. Do for both, and you have your answer

Q5 - 7/10

ARGH, I tried to jump steps on the Equilibrium question, probably best to write things down explicitly

Q6 - 14/14

Q7 - 13/16
- Not sure about the full Ionic equation of Q7bii - Ca(HS03)2 OXIDISES Magnesium.. I think because there were two metals I was confused, could anyone explain this part?
- Got the Reaction of the Base wrong too.
- Question 7cii - Possible Equation - Got that wong apparently it was Benzoic Acid
- The last bit - I thought the rate of dissociation would be too slow so it would make a difference which apparently was wrong.

Q8- 2/10 :O :O :O
NOT sure whats going on :/ :/

I could put my answer for this on a photocopy up, but I'm not sure where it is?
Spoiler:
Show
find the molar quantities of both in the titration, find the molar ratio, find the number of electrons the MnO4- will give up, you can use this to find the number of electrons the VO3- (or V5+) will accept (it's 15 if I remember rightly, or maybe that was a different similar one I've done) and so as there a 5 of the V5+ and 15 electrons are being accepted, then 5V5+=15e- and so each V5+ accepts 3 electrons, 5-3=2, the oxidation state is V2+
Put what I've answered above, italicised the questions I have. All of these are done from memory, so there may be some errors.
16. (Original post by Funtry)
Put what I've answered above, italicised the questions I have. All of these are done from memory, so there may be some errors.
Hi, how are you preparing for this exam?
Have you done all the papers? What else are you doing....need to know how future imperial chemists work
17. After quite a lot of revision I am just getting into the A boundary in the past papers. I have a week to make this a definite comfortable A. This paper is going to be the death of me.
18. (Original post by Funtry)
Put what I've answered above, italicised the questions I have. All of these are done from memory, so there may be some errors.
Thanks Funtry! Yes I went over Question 8 with my Teacher, in some ways it was actually easier than the Previous years, because you only really had to create 1 Equation, and then just do Maths rather than create like 3-4 equations.

If you have any tips on those Equations I got wrong though please advise..

My Teacher said this: "the mistakes you made are only mistakes that aren't really on the syllabus, even if you had another 3 months we wouldn't cover this, a lot of it, is really just working through it like a puzzle from fundamentals"

Can you explain your type of mindset when your doing the Chem Questions? Think this is what I really must nail then in the next few days to be at a Peak and have what the Examiners reports described as a "Chemical Flair"
19. (Original post by MathsNerd1)
Just out of curiosity have you tried any of the questions yet? Sorry about my annotations on the questions as that helps me break it down into the trivial steps

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Apologies MathsNerd not yet!

Today is my Maths and Physics day; tomorrow is Chemistry and Maths so I will be BLITZING the Chemistry questions! I'll do

1. The Questions you put up
2. Specimen Paper or June 2011

then Chem 4 stuff...The Boundaries are so tight there is pretty much no room for Error in Chem 4 :/
20. (Original post by MathsNerd1)
Yeah, I'll post them when I get home tonight

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Now that biology is done and over yaya! Lets get serious with chemistry

Which questions did you post can I do them please

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