Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed)

Original post by posthumus

Thanks guys :biggrin:

& Hopefully I've got it :tongue:

Thanks again :smile:

Well it's a redox equation. Something get's oxidised and something gets reduced, depending on the reduction potential will depend which equation is Red or which is Ox.
I think your E will always be based on the reduction reaction as the forward/reversed cells are based on reduction potentials, but I'm not 100% on that as I don't fully understand your question. The words are all jumpy after a while for me :tongue:

I think you've got it nailed though, that last description looks right to me!

Reply 522

Original post by Mollymod

I think you've got it nailed though, that last description looks right to me!

ahaha I know, I realized at the end I might just be getting too excited and not making much sense :biggrin:

Well is electrode potential of a reduction half-equation ALWAYS greater than the oxidation half-equation ?

If that's the case then it would always be reduction, I think :smile:

But yh in general I think I'm good to move on :biggrin:

& when I do practice questions I should get the hang of it anyway :smile:

(which half-equations to switch).

Reply 523

Original post by posthumus

ahaha I know, I realized at the end I might just be getting too excited and not making much sense :biggrin:

Well is electrode potential of a reduction half-equation ALWAYS greater than the oxidation half-equation ? [QUOTE] Yes. Definitely, it'll always be the more positive one. It means the equation really does want to go that way (more than the other equation)

Original post by posthumus

But yh in general I think I'm good to move on :biggrin:

& when I do practice questions I should get the hang of it anyway :smile:

(which half-equations to switch).

Practice questions really is the way forward.

Guys, how likely is it that they'll ask some Acid/Base titrationy things.
I've been getting a little bit worried about the whole synoptic thing. I feel like my brain will explode with all this information it has to carry for the exam. And this is just Chemistry... :s-smilie:

I realise I've forgotten how to calculate Kb and things, or my calculator is heavily glitching on me.

I tried calculating the pH of a strong base and let's say..
0.1mol dm-3 of NaOH.
I did 0.1/1x10-14 = 1x10-13 and then -log(1x10-13)
is my working right or have I heavily messed up? Because my calculator
then gave me pH -13 o.O

and long equilibrium calculations; I'm paranoid of not knowing absolutely everything, and I have to ace this; I've grown to love Chem too much so I kind of want to do well :redface:

(edited 11 years ago)

Reply 524

GeorgeL3

[QUOTE="Mollymod;42076362"]Well is electrode potential of a reduction half-equation ALWAYS greater than the oxidation half-equation ?

Yes. Definitely, it'll always be the more positive one. It means the equation really does want to go that way (more than the other equation)

Practice questions really is the way forward.

Guys, how likely is it that they'll ask some Acid/Base titrationy things.
I've been getting a little bit worried about the whole synoptic thing. I feel like my brain will explode with all this information it has to carry for the exam. And this is just Chemistry... :s-smilie:

To find the pH of a strong base I think there were two different ways:
1. Work out pOH and do 14 - pOH to get pH.
This just involves using pH = -log[H+] and replacing pH with pOH and H+ with OH-
so pOH = -log0.1 = 1
pH = 14 - 1 = 13
2. Say [OH-][H+]=1x10^-14 and then rearrange it.
[H+] = 1x10^-14 / 0.1 = 1x10^-13
pH = -log1x10^-13 = 13 <- Yeah I guess your calculator must have messed up, have you tried turning it off and on again? haha

Also I would just make sure you know how the sodium thiosulphate titration works with Iodine and also the potassium manganate one with iron since I think they mention them in the specification.

(edited 11 years ago)

Reply 525

Original post by GeorgeL3

Well is electrode potential of a reduction half-equation ALWAYS greater than the oxidation half-equation ?
To find the pH of a strong base I think there were two different ways:
1. Work out pOH and do 14 - pOH to get pH.
This just involves using pH = -log[H+] and replacing pH with pOH and H+ with OH-
so pOH = -log0.1 = 1
pH = 14 - 1 = 13
2. Say [OH-][H+]=1x10^-14 and then rearrange it.
[H+] = 1x10^-14 / 0.1 = 1x10^-13
pH = -log1x10^-13 = 13 <- Yeah I guess your calculator must have messed up, have you tried turning it off and on again? haha

Also I would just make sure you know how the sodium thiosulphate titration works with Iodine and also the potassium manganate one with iron since I think they mention them in the specification.

Yeah, I wont be using my dodgy calculator for the exam. It's so old and rusty and all the numbers have disappeared. I'll post a picture later :P Thanks for that, yeah I've got it right. I'll practice those briefly before the exam but I'll try not to stress too much :smile:

Aha yeah, alright. So back-titration things/Redox Titrations and the 1:5 Fe/MnO4 ratio :smile:

(edited 11 years ago)

Reply 526

Original post by Mollymod

I need BCC :smile:

Almost sure that the B will be Chemistry.
And yeah, it's a lot of memorisation but I like memorising things, it's almost fun when I test myself, although it's not really proving if I'm good at Chemistry or not, it's just a memory game really :P

Yeah, TM's are a bit iffy but thankfully it should be easy to sort out once I fully understand the theory. We've got quite a while left which is good :smile:

I've just started looking at a couple of Unit 1 things for my retake which is 23rd of May. What grades do you need?

I need 3As. I think I am sorted with redox now phew!

Reply 527

Original post by AS01

I need 3As. I think I am sorted with redox now phew!

Ooh that's high :P
What university is this for?

Awesomeness. I'm spending today drawing out all unit 1 mechanisms, and looking at Parts Per Million :smile:

I'm going to power through Mass Spec and Calorimetry this evening. Tomorrow will be Unit 5 day where I'll transition-metal and probably Redox things up :smile:

Reply 528

If anyone is retaking Unit 2, I've made a thread here : http://www.thestudentroom.co.uk/showthread.php?t=2310012 :smile:

Reply 529

Original post by Mollymod

Ooh that's high :P
What university is this for?

Awesomeness. I'm spending today drawing out all unit 1 mechanisms, and looking at Parts Per Million :smile:

I'm going to power through Mass Spec and Calorimetry this evening. Tomorrow will be Unit 5 day where I'll transition-metal and probably Redox things up :smile:

its for medicine so most unis want 3As :tongue:

Hmm that's good! I think I should do the same for mechanisms

Reply 530

Original post by AS01

its for medicine so most unis want 3As :tongue:

Hmm that's good! I think I should do the same for mechanisms

Oh in that case, well done for getting into Medicine! :smile:

So many mechanisms, it's mad!

Reply 531

Original post by Mollymod

Oh in that case, well done for getting into Medicine! :smile:

So many mechanisms, it's mad!

I am not that lucky. I didnt get any offer. I am taking gap year but that's the grade I have to aim for :smile:

Reply 532

David Tennant

Original post by AS01

I am not that lucky. I didnt get any offer. I am taking gap year but that's the grade I have to aim for :smile:

I'm sorry you didn't get in, do you mind me asking where you applied at?

Reply 533

David Tennant

Original post by posthumus

If anyone is retaking Unit 2, I've made a thread here : http://www.thestudentroom.co.uk/showthread.php?t=2310012 :smile:

Thanks posthumous, I can link your forum to my Op if you'd like :smile:

Reply 534

Original post by David Tennant

Thanks posthumous, I can link your forum to my Op if you'd like :smile:

Yh that would be great, thanks :biggrin:

However by the looks of it... not many people are retaking unit 2 ! :tongue:

Reply 535

Original post by posthumus

Yh that would be great, thanks :biggrin:

However by the looks of it... not many people are retaking unit 2 ! :tongue:

or the year 12s haven't woken up yet :P

Original post by AS01

I am not that lucky. I didnt get any offer. I am taking gap year but that's the grade I have to aim for :smile:

Well at least you can get your As at the end of this year and get yourself sorted early. Better luck in a year, you deserve it! :biggrin:

It's good that you're still going for the dream though. Props!

Reply 536

Original post by Mollymod

or the year 12s haven't woken up yet :P

Ahaha yh I was thinking ! :biggrin:

Last year I would start studying for my exams like 1 or 2 weeks before them.... boy did I learn by lesson :tongue:

Reply 537

Original post by posthumus

Ahaha yh I was thinking ! :biggrin:

Last year I would start studying for my exams like 1 or 2 weeks before them.... boy did I learn by lesson :tongue:

at least you learned before it was too late :P
And you had the chance for January exams; for some, January just isn't an option. It's either June or nothing.

I revised last year, but I revised and didn't make sure that I had properly understood things. It's all well and good knowing what to say, but it's about knowing when, how and why to say it. My teacher famously says 'skip out all the bs of a question' when it's full of words that you don't really need to do the calculation, but I took it too far and stopped reading questions altogether; and really, that's how I lose my marks which accounts for MCQ being my worst section :P

(edited 11 years ago)

Reply 538

blossomx

Does anyone know if we need to know the names and structures of different amino acids? Such as glycine, alanine, cysteine, phenylalanine, and aspartic acid. Thank you in advance. :smile:

Reply 539