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ocr a f325 revision thread

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Reply 840
Avatar for Aliceo
Aliceo
2
Original post by MathsNerd1
Okay I've just had a look at the book and it looks like they're both used, the PEM is an acidic one whereas the book is an alkaline one, which if you think about it makes some sense as the OH- ions are passing through instead of the H+ ions that pass through in the acidic one to react with the H+ ions formed at the negative terminal.

Also I always remember in aq things are represented as ions which then can cancel off if they're spectator ions and solids can't be split into their ions :smile:


Thank you! :smile: So it's pretty much the same, but instead of H+ crossing the membrane to get to the cathode, OH- crosses the membrane to get to the anode where the H+ is?

So, at the anode: H2 + 2OH- --> 2H2O + 2e-
And at the cathode: 1/2O2 + H2O + 2e- --> 2OH-

I think I'm beginning to understand... Hopefully! :tongue:
Original post by Aliceo
Thank you! :smile: So it's pretty much the same, but instead of H+ crossing the membrane to get to the cathode, OH- crosses the membrane to get to the anode where the H+ is?

So, at the anode: H2 + 2OH- --> 2H2O + 2e-
And at the cathode: 1/2O2 + H2O + 2e- --> 2OH-

I think I'm beginning to understand... Hopefully! :tongue:


Yeah that sounds right to me although I never know which one is the cathode and anode, I just write the positive terminal and negative terminal :tongue:

I'll probably just "wing" this part of the syllabus as it shouldn't be too hard to remember, I hope! :biggrin:
Reply 842
Avatar for D4rth
D4rth
9
Original post by MathsNerd1
Yeah that sounds right to me although I never know which one is the cathode and anode, I just write the positive terminal and negative terminal :tongue:

I'll probably just "wing" this part of the syllabus as it shouldn't be too hard to remember, I hope! :biggrin:


aNode - Negative

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Original post by D4rth
aNode - Negative

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Of course because an anode produces the negative ions whereas the cathode produces the positive ions, thanks :biggrin:
Reply 844
Avatar for Funtry
Funtry
15
Just did my first PP, June 2010, and got 90/100 (A=71, A*=~79, more likely 82) :smile: missed one mark for changing my Kc equation from having a squared on top to having no power, but that was ECF of 3 marks out of four, which was lucky!! Also there was a horrible buffer solutions question, and a question on fuel cells :frown: otherwise the missed marks were stupid reading errors or putting equilibrium signs instead of fully forward arrows. All in all I'm pleased with that result, as the UMS works out to roughly full UMS and I only need 90!!
Original post by Funtry
Just did my first PP, June 2010, and got 90/100 (A=71, A*=~79, more likely 82) :smile: missed one mark for changing my Kc equation from having a squared on top to having no power, but that was ECF of 3 marks out of four, which was lucky!! Also there was a horrible buffer solutions question, and a question on fuel cells :frown: otherwise the missed marks were stupid reading errors or putting equilibrium signs instead of fully forward arrows. All in all I'm pleased with that result, as the UMS works out to roughly full UMS and I only need 90!!


Can you provide me with your great ability for Chemistry, I could use it for these 3 exams! :tongue:


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Reply 846
Avatar for Funtry
Funtry
15
Original post by MathsNerd1
Can you provide me with your great ability for Chemistry, I could use it for these 3 exams! :tongue:




Good job I'm not doing ChemU1 for the fourth time this Thursday :tongue: It's not real chemistry!! I've loved this year though. You want any help in U2/4/5? :smile:
Reply 847
Avatar for Better
Better
8
Original post by Funtry
Just did my first PP, June 2010, and got 90/100 (A=71, A*=~79, more likely 82) :smile: missed one mark for changing my Kc equation from having a squared on top to having no power, but that was ECF of 3 marks out of four, which was lucky!! Also there was a horrible buffer solutions question, and a question on fuel cells :frown: otherwise the missed marks were stupid reading errors or putting equilibrium signs instead of fully forward arrows. All in all I'm pleased with that result, as the UMS works out to roughly full UMS and I only need 90!!


Lol Read Imperial. Read you rejected UCL and Kings. Was thinking this guy is a beast.

Then read Malia 2013....Haha priceless. Lad points obtained, but intellectual points go down hill.
Reply 848
Avatar for Funtry
Funtry
15
Original post by Better
Lol Read Imperial. Read you rejected UCL and Kings. Was thinking this guy is a beast.

Then read Malia 2013....Haha priceless. Lad points obtained, but intellectual points go down hill.


Haha, I like drinking, what can I say? ;D

Plus who says I'm not going out there to visit the ruins? :pierre: (I'm not but still.)
Original post by Funtry
Good job I'm not doing ChemU1 for the fourth time this Thursday :tongue: It's not real chemistry!! I've loved this year though. You want any help in U2/4/5? :smile:


Yeah it's all just regurgitation of the facts, incredibly boring! And well would you be able to be show how we can prove the oxidation states of a compound change by using the concentrations and volumes? I feel that could possibly be a question that'll confuse me a lot :-/


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Reply 850
Avatar for Better
Better
8
Original post by Funtry
Haha, I like drinking, what can I say? ;D

Plus who says I'm not going out there to visit the ruins? :pierre: (I'm not but still.)


Imagine haha! Brilliant. So annoyed I didn't get into Imperial. Oh well.... I will have better girls at UCL bro!!! So :banana:
Reply 851
Avatar for Better
Better
8
Original post by Funtry
Good job I'm not doing ChemU1 for the fourth time this Thursday :tongue: It's not real chemistry!! I've loved this year though. You want any help in U2/4/5? :smile:


Funtry if you are good at Unit 4 that would help. I only got 49/60.

So frustrating. I need at least 6 more marks. If you have any tips that would be decent.
Original post by MathsNerd1
Hmm, if its in the textbook I'll say that there's a possibility of it appearing in the exam :-/


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Name the catalyst used in the contact process and how do catalysts work (3)
Original post by otrivine
Name the catalyst used in the contact process and how do catalysts work (3)


Do we actually need to know how the catalyst will work in each reaction and isn't it something like V2O5? Vanadium (V) oxide ?
Original post by MathsNerd1
Do we actually need to know how the catalyst will work in each reaction and isn't it something like V2O5? Vanadium (V) oxide ?


Yes thats the correct catalyst :smile:


Better to know it as they could potentially ask that as an application question.

ask me one :smile:
Reply 855
Avatar for Better
Better
8
Original post by MathsNerd1
Do we actually need to know how the catalyst will work in each reaction and isn't it something like V2O5? Vanadium (V) oxide ?


Yes they work in two ways.

1. As absorbants - they provide a surface for the reactants to react, and then release them once the reaction as has occured. Example Fe catalyst in Haber Process for Ammonia.

2. Due to variable oxidation states, they can accept electrons and form intermediates. Thus providing an alternate path with an lower activation energy. Example Fe(Iron) Catalyst in Organic Chemistry in the Monohalogenation of Benzene.
Original post by Better
Yes they work in two ways.

1. As absorbants - they provide a surface for the reactants to react, and then release them once the reaction as has occured. Example Fe catalyst in Haber Process for Ammonia.

2. Due to variable oxidation states, they can accept electrons and form intermediates. Thus providing an alternate path with an lower activation energy. Example Fe(Iron) Catalyst in Organic Chemistry in the Monohalogenation of Benzene.


I see, that makes sense just didn't know that could be asked in the exam, thanks :smile:
Original post by otrivine
Yes thats the correct catalyst :smile:


Better to know it as they could potentially ask that as an application question.

ask me one :smile:


Thanks and fair enough, I'll touch up on them then and I would normally but I'm just too tired right now so I think I'll pass this time.
Original post by MathsNerd1
Thanks and fair enough, I'll touch up on them then and I would normally but I'm just too tired right now so I think I'll pass this time.


Tomorrow>!?
Original post by otrivine
Tomorrow>!?


Maybe? I've got unit 1 coming up on Thursday so that'll be my priority right now as well as getting through all the Maths I was set this week and some STEP questions too.

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