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ocr a f325 revision thread

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Original post by DudeBoy
Yeah I am feeling pretty confident for f325 tbh need 118 ums for an A and I am resitting F324, just praying that I don't make so many stupid mistakes like I did in the mock :smile:


Yeah, let's just go in and smash it!!! :biggrin:
Reply 1641
Avatar for Better
Better
8
Original post by MathsNerd1
Yeah, let's just go in and smash it!!! :biggrin:


MathsNerd I've seen you on this and the C3/C4 Thread for the last 4 weeks.

2 more weeks left brah!! Let's do this!!!!
Original post by Better
MathsNerd I've seen you on this and the C3/C4 Thread for the last 4 weeks.

2 more weeks left brah!! Let's do this!!!!


Yeah I'm on them all and I've got 3 more weeks left! :tongue: Let C4 be a right curveball as it'll be fun and enjoyable, plus make the grade boundaries a lot easier too :tongue:
just did the jan 2012 paper and got 50 which is not even an E :/ need a B in this module for uni. I'm finding it really difficult and there's not long to go now, I even managed a C in the mock! any tips?
Original post by MathsNerd1
Yeah, let's just go in and smash it!!! :biggrin:


Can I join? I need to get an A* in this :P
I hope my practical mark doesn't get moderated though
Original post by chignesh10
Can I join? I need to get an A* in this :P
I hope my practical mark doesn't get moderated though


I suppose so :wink: Aha, nah its fine we're all going to smash it! As there really isn't much content to learn since I printed out the spec today and realised its pretty simple really, I know mine will be as there are only 2 in my group, so it'll definitely all go :-/
Original post by MathsNerd1
I suppose so :wink: Aha, nah its fine we're all going to smash it! As there really isn't much content to learn since I printed out the spec today and realised its pretty simple really, I know mine will be as there are only 2 in my group, so it'll definitely all go :-/


I really like your motivation to succeed, really well done :smile:
Original post by otrivine
I really like your motivation to succeed, really well done :smile:


Thanks, I don't see the point in not being motivated in the exams you plan to sit as you're clearly not going to succeed with that mind-set, always thinking positive! :biggrin:
Reply 1648
Avatar for Namod
Namod
10
Original post by bluedate
C = 1.17x24 = 28.08 which is N2

mr of H2O2 is 34
so n x mr
:smile:


What formula is this?
Reply 1649
Avatar for Namod
Namod
10
Original post by DudeBoy
Jan 13
Q1a.v. Mass of atom x avagadros no.
(8.64x10^-23)x(6.02x10^23)=52.01
Q7b. This is just using prior knowledge of reactions.
cii. This is from knowing that H2SO4<-->HSO4(-)<-->SO4-2
8cii. Look at stage 3. You are given a conc and volume, so you can work out moles with CV/1000.
Look at stage 1. You are given a mass, and you can find the mr. Use m/mr to find n(V).
Divide by 5 because 10cm3 of the original solution was titrated so you have 1/5 of the number of moles in that solution.
Ratio is worked out by divided both sets of moles.
From this formulate the equation, knowing that 5V and 3MnO4 are reacted.


Q1a.v. Mass of atom x avagadros no.
(8.64x10^-23)x(6.02x10^23)=52.01

What formula is this?
Reply 1650
Avatar for Namod
Namod
10
3 Questions:
June 2012
3(c)(ii) - How to do that?

Jan 2011:
7(a)(i) - How to get moles of O2

June 2010:
7(b) - Why in the mark schemes they times the concentration of H2O2 by 34
(edited 10 years ago)
Original post by Namod

What formula is this?


I'm assuming Mr/Avagadros=Mass of a single atom
Reply 1652
Avatar for Namod
Namod
10
Original post by DudeBoy
I'm assuming Mr/Avagadros=Mass of a single atom



Yep thanks just derived it.
Original post by Namod
3 Questions:
June 2012
3(c)(ii) - How to do that?

Jan 2011:
7(a)(i) - How to get moles of O2

June 2010:
7(b) - Why in the mark schemes they times the concentration of H2O2 by 34

June 12
3cii. Ka=[H+][CH3CH2CH2COO-]/[CH3CH2CH2COOH]
Ka x ([CH3CH2CH2COOH]/CH3CH2CH2COO-])=[H+] (Work this out by rearranging)

Now you need the concentration of both Butanioc acid and Butanoate,
CH3CH2CH2COOH+NaOH-->CH3CH2CH2COO-(Na+) + H2O
Moles of CH2CH2COO- = 50 x 0.05/1000 = 2.5x10^-3
Moles of CH2CH2COOH =0.0125
Now you have to minus the Butanoate as well because that is formed from Butanoic acid.
So 0.0125-2.5x10^-3=0.0100
Now to get concentration do molesx1000/volume (VOLUME IS 100 NOT 50)
You get 0.1 and 0.025.
Plug them into the rearranged Ka equation to get [H+] and then do -log[H+] to get pH.
Reply 1654
Avatar for Namod
Namod
10
Original post by DudeBoy
June 12
3cii. Ka=[H+][CH3CH2CH2COO-]/[CH3CH2CH2COOH]
Ka x ([CH3CH2CH2COOH]/CH3CH2CH2COO-])=[H+] (Work this out by rearranging)

Now you need the concentration of both Butanioc acid and Butanoate,
CH3CH2CH2COOH+NaOH-->CH3CH2CH2COO-(Na+) + H2O
Moles of CH2CH2COO- = 50 x 0.05/1000 = 2.5x10^-3
Moles of CH2CH2COOH =0.0125
Now you have to minus the Butanoate as well because that is formed from Butanoic acid.
So 0.0125-2.5x10^-3=0.0100
Now to get concentration do molesx1000/volume (VOLUME IS 100 NOT 50)
You get 0.1 and 0.025.
Plug them into the rearranged Ka equation to get [H+] and then do -log[H+] to get pH.


Didnt get why you minus
(edited 10 years ago)
Original post by Namod
3 Questions:
June 2012
3(c)(ii) - How to do that?

Jan 2011:
7(a)(i) - How to get moles of O2

June 2010:
7(b) - Why in the mark schemes they times the concentration of H2O2 by 34


Jan 2011
7ai. Use CV/1000 to get S2O3(2-) used.
=2.46x10^-5

Look at the equations, 2 moles of S2O3 form 2 moles of I(-)
So I(-) = 2.46x10^-5
2 mole of I(-) reacts 2 moles of Mn(OH)3 so =2.46x10^-5.
4 moles of Mn(OH)3 is formed by 1 mole of O2, so O2 moles = mole of O2 = 2.46x10^-5/4.
=6.15x10^-6
Use CV/100 to get conc of O2.
Original post by Namod
Didnt get why you minus


You minus it because some CH3CH2CH2COOH is used to make CH3CH2CH2COO-
Reply 1657
Avatar for Namod
Namod
10
Original post by DudeBoy
You minus it because some CH3CH2CH2COOH is used to make CH3CH2CH2COO-


ok thanks one last one to answer.
you are awesome
Original post by Namod
3 Questions:
June 2012
3(c)(ii) - How to do that?

Jan 2011:
7(a)(i) - How to get moles of O2

June 2010:
7(b) - Why in the mark schemes they times the concentration of H2O2 by 34


June 2010
7b.
You times by 34 as that is the Ar of H2O2
2(1)+2(16)
Reply 1659
Avatar for drplease
drplease
Do we have to know the indicators?? It says on the spec guess I will have to cram it...

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