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# ocr a f325 revision thread watch

1. (Original post by louci)
Guyyyyyss
does anyone have the jan 13 ms ???
Attached.
Attached Images
2. F325_MS_Jan13.pdf (561.5 KB, 44 views)
3. (Original post by sidmanny)
I worked out how to do it, using kw again but I got the right answer this time. I dunno how I didn't get this answer first time, must have forgotten to log it or something.
So you're finding pH, [H+]= kw/[OH-]
[OH-]=100x[H+], kw=1.00x10^-14
so [H+]=1.00x10^-14/100[H+]
[H+]^2= 1.00x10^-14/100
[H+]= square root of 1.00x10^-14/100
Then you minus log the [H+], -log10(1x10-8
which gives 8
what question is this the answer to?
4. (Original post by DudeBoy)
Using quadratic equation to find pH

Ka=[H+][A-]/[AH]
Ka=[H+]^2/[AH-H+]
Ka[AH-H+]=[H+]^2
[H+]^2-Ka[-H+]-Ka[AH]
I doubt it will come up but you never know
You can't seperate the Ka[AH-H+] to Ka[-H+]-Ka[AH], or if you can how do you know. lol
5. (Original post by Funtry)
Good, thanks I was getting worried. Also they put [H+] as 1.99x10^-9, yet I got 1.95x10^-5, same error?
Yes, I got that too. I think the specimen paper is pretty poor. A lot of the questions seemed as though they belonged to F324 with all those benzene rings.
6. ok so if anyone could help me with this I'd be grateful... I find it difficult to rearrange formulas, but I find it easy when they are put into the triangle formula format...how do I put the Gibbs Free energy equation into a triangle equation format? and what would ds be equal to ? thx in advance..

I am mainly referring to question 5d on the june 2011 paper..
7. (Original post by icebergs)
Can someone explain buffers for me? i get really confused
so lets take the buffer for blood- which has to remain at the pH of 7.45
So its carbonic acid, H2CO3 dissociating into HCO3- and H+
H2 CO3 ⇄ HCO3- + H+

Definition for buffer solution: a solution (made from a weak acid and its conjugate base) that can minimise the change in pH when small amounts of alkali(OH-) and acid (H+) is added

so when OH- added this reacts with the H+ in the blood it makes H2O. The equilibrium shifts to the right to make more H+'s, cos some have been lost.

when H+ is added, it reacts with HCO3- and makes more H2CO3. This shifts the equilibrium to the left. So all this ultimately controls the pH.

Hoped that all helped
8. with complex ions like [Ni (Cl)4] what is the bond angle and shape?

In my revision guide it says tetrahedral with angle of 109.5 degrees
but in my notes from class they say square planar with angle of 90.

Which is right?

9. (Original post by icebergs)
Can someone explain buffers for me? i get really confused
o lets take the buffer for blood- which has to remain at the pH of 7.45
So its carbonic acid, H2CO3 dissociating into HCO3- and H+
H2 CO3 ⇄ HCO3- + H+

Definition for buffer solution: a solution (made from a weak acid and its conjugate base) that can minimise the change in pH when small amounts of alkali(OH-) and acid (H+) is added

so when OH- added this reacts with the H+ in the blood it makes H2O. The equilibrium shifts to the right to make more H+'s, cos some have been lost.

when H+ is added, it reacts with HCO3- and makes more H2CO3. This shifts the equilibrium to the left. So all this ultimately controls the pH.

Hoped that all helped
10. it's square planar and has 90 degrees angles. http://img3.imageshack.us/img3/1020/picture35s.png
11. (Original post by earthtokaz)
with complex ions like [Ni (Cl)4] what is the bond angle and shape?

In my revision guide it says tetrahedral with angle of 109.5 degrees
but in my notes from class they say square planar with angle of 90.

Which is right?

It's tetrahedral.
12. (Original post by Nuna)
ok so if anyone could help me with this I'd be grateful... I find it difficult to rearrange formulas, but I find it easy when they are put into the triangle formula format...how do I put the Gibbs Free energy equation into a triangle equation format? and what would ds be equal to ? thx in advance..

I am mainly referring to question 5d on the june 2011 paper..
anyone ??
13. (Original post by Nuna)
anyone ??
What triangle equation.
14. (Original post by treebarky)
o lets take the buffer for blood- which has to remain at the pH of 7.45
So its carbonic acid, H2CO3 dissociating into HCO3- and H+
H2 CO3 ⇄ HCO3- + H+

Definition for buffer solution: a solution (made from a weak acid and its conjugate base) that can minimise the change in pH when small amounts of alkali(OH-) and acid (H+) is added

so when OH- added this reacts with the H+ in the blood it makes H2O. The equilibrium shifts to the right to make more H+'s, cos some have been lost.

when H+ is added, it reacts with HCO3- and makes more H2CO3. This shifts the equilibrium to the left. So all this ultimately controls the pH.

Hoped that all helped

Hi,

in titration curves how do we work out the equivalence point
15. (Original post by Namod)
What triangle equation.
I mean you know how n=m/mr is represented in a triangle in the text book, how do I do that for the gibbs free energy equation?
16. (Original post by Funtry)
http://www.ocr.org.uk/Images/81033-u...s-specimen.pdf

On question 2d, does anybody else get 0.013, instead of 0.13?
Can you (or anyone) explain question 1 a iii to me please?
17. (Original post by Pride)
Write an equation and you'll be able to see it. Every mole of H2SO4 reacts with a monobasic base to form 2 moles of water, so twice the enthalpy change. The salt ions are just spectator ions.

well yes, read the definition of standard enthalpy change of neutralisation. It's all about the one mole of H2O, so you have to divide by how many moles of water you've formed.
Where would the extra oxygen come from? Unless one mole of di basic acid reacts with two moles of monobasic base?
18. So for a reaction to be feasible ^G<0
When is it spontaneous?
19. (Original post by eggfriedrice)
It's tetrahedral.
From my notes it tends to be only Ni/Pt metal ion complexes which take the square planar shape with 90 degree bond angles. The rest such as Co or Cu as central metal ion use tetrahedral with 109.5 bond angles.
20. (Original post by Nuna)
I mean you know how n=m/mr is represented in a triangle in the text book, how do I do that for the gibbs free energy equation?
Free gibbs isn't triangle because these a minus sign

G=H-TS
G+TS=H
(G-H)/-T=S
(G-H)/-S=T

21. (Original post by H0ls)
From my notes it tends to be only Ni/Pt metal ion complexes which take the square planar shape with 90 degree bond angles. The rest such as Co or Cu as central metal ion use tetrahedral with 109.5 bond angles.

So NiF4, is it square planar then?

in titration right, do you add water +alkali + acid into conical flask or is it only alkali and acid?

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