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

1. (Original post by haydyb123)
I'm getting 42.9%, what is the answer?
21.6 or 21.7 %

My guess would be that they assume 2 moles of that na2feo4 produced
Think about it fe2 in the LHS
But then that would have needed the whole equation
2. (Original post by Hydro.ZX)
Small post so will probably get ignored, so i'm quoting it.
I know that all the papers are really incredibly similar, lots of borne harber cycles, pH calculations, and gibbs free energy equations- but are there not a few areas you could look at which you find slightly more tricky. Do a few more worksheets on calculations or make sure you can answer long answer questions e.g. of buffers.

Good luck Wed; sounds like your confident
3. (Original post by arvin_infinity)
1. Artists between the 13th and the 19th Centuries used a green pigment called verdigris. The artists made the pigment by hanging copper foil over boiling vinegar.
A sample of verdigris has the formula [(CH3COO)2Cu]2.Cu(OH)2.xH2O.?Analysis of the sample shows that it contains 16.3% water by mass.?Calculate the value of x in the formula.

answer is 5
Didnt know how to do it! Someone explain plss
Hope we get easier q than this!
I might be talking gibberish but this is how I worked it out:

I found the mr of anhydrous verdigris first which was 460.5

because 16.3% of the the mass was water then 460.5 is 83.7% (100-16.3)of the molecules mass. This means the total mass is 460.5/0.837= 550.18 g/mol

550.18*0.163 = 89.67 g/mol

89.67/18 = 5 H20 molecules/mol
4. (Original post by arvin_infinity)
21.6 or 21.7 %

My guess would be that they assume 2 moles of that na2feo4 produced
Think about it fe2 in the LHS
But then that would have needed the whole equation
very good point, I see it now, bit naughty to not have an equation though!
5. (Original post by Diddy91)
Can someone please explain this question to me of the january 2011 exam (2C).
6FeSO4 + 7H2SO4 + Na2Cr2O7 --> 3Fe2(SO4)3 + Cr2(SO4)3 + Na2SO4 + 7H2O and question is show that oxidation and reduction have both taken part in this redoz reaction? Now I understand you are targeting Cr and Fe as these are transition elements. But I am not getting the correct values. My oxidation states are coming in at like +10 and +15!!
Cr has been reduced from +6 to +3

Fe has been oxidised from +2 to +3

In these molecules I think Sulphur is in the +6 oxidation state is the key to working it out
6. (Original post by haydyb123)
If you have a specific question I'll help you out, as those topics are pretty large to go over completely!
LOL. ITS rate determining step! cant do it, i always seem to get different compounds....is there some sort of rule??

thank u! x
7. How would you guys answer the question "State how the student would identify the end point of an iodine/thiosulphate titration?"

Im pretty sure its add starch and it'll go from blue-black to colourless, but the mark scheme i has says blue-black to white do NOT allow colourless... It has me a bit confused.
8. (Original post by *QueenBeee)
LOL. ITS rate determining step! cant do it, i always seem to get different compounds....is there some sort of rule??

thank u! x
There is no rules, just make it up. Make sure all your molecules balance up as you do it and make sure your 2 step reaction cancels down to give the overall reaction.
Your molecules from the rate equation are involved in the step 1 (the slowest step), so any molecules that are not involved in step 1 but are in the overall reaction will come in step 2

Also there is more than one possible answer for these sort of Q so just because yours is not the same as the mark scheme doesn't mean it is incorrect.
9. (Original post by jontylol)
How would you guys answer the question "State how the student would identify the end point of an iodine/thiosulphate titration?"

Im pretty sure its add starch and it'll go from blue-black to colourless, but the mark scheme i has says blue-black to white do NOT allow colourless... It has me a bit confused.
No idea

Is the step before is when you react Cu2+ with I-. This forms I2 and CuI(white precipitate)
Maybe this is an explanation
I would have thought they would allow it goes to colourless though?
10. (Original post by CoventryCity)
No idea

Is the step before is when you react Cu2+ with I-. This forms I2 and CuI(white precipitate)
Maybe this is an explanation
I would have thought they would allow it goes to colourless though?
Hmm yeah it is... It says the iodine formed was titrated so i don't know whether that means taken out and titrated or what. Oh well im just gonna go with badly worded question hah :P
11. Could someone explain to me the changes that take place at each electrode in a hydrogen-oxygen fuel cell? I really can't get my head around it for some reason. Thank you
12. Someone make an epic list of all ligands shapes and their angle

to start off
1. Octahedral e.g. [Fe(OH)6]2+ 90 degress
13. [CuCl4]2- Tetrahedral bond angles 109.5
14. Does anyone else have a source of questions other than legacy papers?
15. (Original post by haydyb123)
Does anyone else have a source of questions other than legacy papers?
Im working my way through the pack of past paper questions posted on page 1. (lol alliteration) Theres about 140 questions in there.
16. do we need to know and use the term mole fraction?
17. (Original post by jontylol)
Im working my way through the pack of past paper questions posted on page 1. (lol alliteration) Theres about 140 questions in there.
thanks man, I'll check it out!
18. (Original post by katie_3000)
really appreciate thos papers! thanks!
how do you get to the revision questions?
19. does anyone know what the grade boundary was for jan 2011?
20. (Original post by tallysingh)
does anyone know what the grade boundary was for jan 2011?
65 - A

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