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# Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch

1. Could they ask us to name a side effect of platin as a quick 1 mark question?
2. (Original post by CoventryCity)
0.167/ 55.5 = 3.009x10-3 moles of iron
0.487/ 324.6 =1.5x10-3 moles of X

Molar ration of Fe:X is 2:1

2Fe + ?Cl2 -----> X
So the compound X has Fe2 in it 324.6 - (55.5 x2)= 213.6
213.6 / 35.5 = 6.02 approx 6
So it is Fe2Cl6
Awesome thanks man, I calculated moles and then started going down the empirical formula route for some reason, thanks
3. (Original post by BA1)
I haven't done any of the old-spec papers this time. I did a lot of them for F324 and it didn't help to be honest, the old-spec papers are a different style and a lot more simple.

We only have two F325 papers (and a specimen) to work from, so I've been looking at all the stretch/challenge boxes in the Heinemann textbook and doing a few unstructured exercises from university textbooks. That will surely be a bigger help for me.
Yeah exactly, is it possible for you to scan some of those questions and email them?
4. (Original post by raj16)
wenever i ave a titration question i got through the same stages
1. MOLES
look for wen they give u a conc and a volume, so in this qu they give u 0.02moldm3 of KMnO4 and the volume 23.45cm3.
Use n=cv and u shuld get 4.69x10-4 mols of KMn04

2.Ratios
By using the equation given u can compare the number of moles. So Mn04 2:5 H2O2.
so divide the answer we got above by 2, thats so u get 1 mole and then times by 5. 1.1725x10-3

1 thing to look out for in the volumes, the answer we've worked out is in 25cm3, so in 250cm3 its 10X as more, 1.1725x10-2. This is the moles of H2O2 in 250cm3.

3.Units
Now they want the answer in g/dm3. So i think about this in terms of units now. Where can i get grams from? mols=mass/Mr

So 1.1725x10-2 /34= 0.39865g
Right at the beginnin of the qu they tell u that u diluted the soultion in 25cm3.
So we ave grams and cm3, divide cm3 by 1000 u get answer in dm3.
25/1000=0.025DM3
Using the units again g/dm3, i see the / meanin divide.
FINALLY!!

0.39865/ 0.025= 15.97g/dm3

Really hope i didnt confuse u further
cheers
5. in the equilibrium amount questions where the equilibriums concentrations are in tables

how do you find the amount formed from the amount reacted

do you just add them? but then if its a 1:1 ratio is doesn't work?...so do you just multiply them by the ratios?
6. (Original post by CoventryCity)
0.167/ 55.5 = 3.009x10-3 moles of iron
0.487/ 324.6 =1.5x10-3 moles of X

Molar ration of Fe:X is 2:1

2Fe + ?Cl2 -----&gt; X
So the compound X has Fe2 in it 324.6 - (55.5 x2)= 213.6
213.6 / 35.5 = 6.02 approx 6
So it is Fe2Cl6
You can also work out the mols of cl2 as its mass will be 487-167=320
7. whats a really hard born haber question? give me an example plzz
8. in buffers calculations does the conc of salt=conc of conjgate base?
9. (Original post by haydyb123)
I'm just assuming 250cm is volume of entire buffer mixture?

0.25 mol dm3 of ethanoate
and 0.125 mol dm-3 ethanoic acid

[H+] = 1.7x10-5 x 0.125 = 0.0000085 -log = 5.07
0.25
I don't understand this?

I would have done 0.125 / (250/1000)= 0.5 moldm-3 enthanoate
Then the concentration of the acid is given as 1.0 moldm-3 acid

[H+] = 1.7x10-5 x ( 1/0.50) = 3.4x10-5
-log[3.4x10-5] = 4.5
10. (Original post by raj16)
wenever i ave a titration question i got through the same stages
1. MOLES
look for wen they give u a conc and a volume, so in this qu they give u 0.02moldm3 of KMnO4 and the volume 23.45cm3.
Use n=cv and u shuld get 4.69x10-4 mols of KMn04

2.Ratios
By using the equation given u can compare the number of moles. So Mn04 2:5 H2O2.
so divide the answer we got above by 2, thats so u get 1 mole and then times by 5. 1.1725x10-3

1 thing to look out for in the volumes, the answer we've worked out is in 25cm3, so in 250cm3 its 10X as more, 1.1725x10-2. This is the moles of H2O2 in 250cm3.

3.Units
Now they want the answer in g/dm3. So i think about this in terms of units now. Where can i get grams from? mols=mass/Mr

So 1.1725x10-2 /34= 0.39865g
Right at the beginnin of the qu they tell u that u diluted the soultion in 25cm3.
So we ave grams and cm3, divide cm3 by 1000 u get answer in dm3.
25/1000=0.025DM3
Using the units again g/dm3, i see the / meanin divide.
FINALLY!!

0.39865/ 0.025= 15.97g/dm3

Really hope i didnt confuse u further
hey thnx!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!
but can u explain what g/dm3 means?!
11. (Original post by raj16)
in buffers calculations does the conc of salt=conc of conjgate base?
Yes I think so as the salt completely dissociates
12. (Original post by 786girl)
hey thnx!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!
but can u explain what g/dm3 means?!
grams per dm3
It is the units of density I think
13. (Original post by raj16)
in buffers calculations does the conc of salt=conc of conjgate base?
yes
14. (Original post by hellosarah)
OGHHH, YES, SAME!!! And now i am freaking out over this. I don't think i will ever get over yesterday. Never.
HaHa same here, hope tomorrow is better. F215 was horrific
15. (Original post by BA1)
Ahh yes, I forgot that. I probably did get over 48, but I'm not resitting F324 so can't get the A*. Doesn't matter, I only need an A!
What if you got 46 or 47? surely then it is still possible?

BA1 you have not looked at the old papers?

I am doing the Stretch and Challenge questions in the PhilipAllan book written by the examiners. Those questions really do challenge onself! ahh

Are you doing C3 on Thurs as well?
16. (Original post by 786girl)
hey thnx!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!
but can u explain what g/dm3 means?!
Grams per dm3, so theres that many grams in 1 dm3
17. Can someone explain enthalpy change of solution to me? I don't understand why they put enthalpy change of solution with enthalpy change of hydration on the same side in that cycle in the book, page 175.
18. Can someone please tell me an easy way to convert gdm-3 into moldm-3? And is it the same for liquids and gases?
19. Has anyone got any useful tips or revision notes? I would be very grateful
Good luck to everyone re-taking this module! I Don't actually need a better mark in this exam, I got a C last time around, if I get at least a C in F324 then I get my B grade in Chemistry A-level. Wish I knew this sooner other than re-taking this one!
20. hey guys, you see in the June 2010 paper? The very last question, number 7(b), I have no idea why the moles of H2O2 in 250cm^3 are multiplied by 40?

Hope someone can help me

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