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

1. can someone help me please?

on page 153 of the text book, the worked example, says that there is about 20 times more hydrogen carbonate ions in the blood than there is carbonic acid. but then the ratio at the bottom says 10.8/1 ?
?
surely that would mean there was only TEN times as much?

Help appreciated!
2. (Original post by student777)
But surely you can just get that from oxidation numbers? Eg if it's Cl- it has oxisation state -1

BrO3- + ....Br- + ....H+ --> ....Br2 + ....H2O

There aren't any charges on the RHS?
Agreed so you must make the charge on the LHS 0 as well

on page 153 of the text book, the worked example, says that there is about 20 times more hydrogen carbonate ions in the blood than there is carbonic acid. but then the ratio at the bottom says 10.8/1 ?
?
surely that would mean there was only TEN times as much?

Help appreciated!
I asked this earlier, I have no idea
4. Thanks i thought that but i just wanted to make sure, sorry about all the questions...can someone explain enthalpy change of solution and its relationship with lattice enthalpy and hydration enthalpy please ??
5. (Original post by CoventryCity)
I asked this earlier, I have no idea
maybe its a mistake? or im hoping so....id rather think the textbook is wrong than i dont understand stuff the day before the exam
6. do we have to know the manganate + iron, cu+I equations? also wen ur asked to draw a half cell wen do use a Pt electrode instead?

Thanks
7. (Original post by student777)
But surely you can just get that from oxidation numbers? Eg if it's Cl- it has oxisation state -1

BrO3- + ....Br- + ....H+ --> ....Br2 + ....H2O

There aren't any charges on the RHS?
That's where your cheeky H+ come in handy

So you know from oxidation numbers Br is +5 and is going to gain 5 electron as it is being reduced to form Br2

So therefore you need 5 electrons provided by Br- so

BrO3^- + 5Br^- + 6H^+ -> 3Br2 + 3 H2O

Charges balances because charges on the left cancel out
do you see now?
maybe its a mistake? or im hoping so....id rather think the textbook is wrong than i dont understand stuff the day before the exam
Yes, it's a mistake and the ratio is approximately 10. There are LOADS of mistakes in the textbook unfortunately.

Good luck to everyone anyway! I need 79/150 UMS for a grade A, which should equate to approx. 45-55 raw marks. I'm still revising a lot though, you never know what OCR will throw at us (especially after January's F324 paper...)
9. (Original post by M_I)
Which one is it?

How do you figure it out?
the colour change is from purple ((MnO4)--charge -1) to yollow (Fe3+), the very pale pink of the Mn2+ does not show

edit: -ve??? what did i do wrong???
10. (Original post by cws121)
Thanks i thought that but i just wanted to make sure, sorry about all the questions...can someone explain enthalpy change of solution and its relationship with lattice enthalpy and hydration enthalpy please ??
Enthalpy change of solution is the enthalpy change when 1 mole of a compound dissolves in water

This is done by breaking the ionic compound into its gaseous ion, this is the opposite of lattice enthalpy so has the same magnitude just a different sign

The the gaseous ions are dissolved into water so become aqueous ions in water (this is hydration)

Enthalpy change of solutions can be worked out using born haber cycles if you have the values for Lattice enthalpy and hydration
11. (Original post by BA1)
Yes, it's a mistake and the ratio is approximately 10. There are LOADS of mistakes in the textbook unfortunately.

Good luck to everyone anyway! I need 79/150 UMS for a grade A, which should equate to approx. 45-55 raw marks. I'm still revising a lot though, you never know what OCR will throw at us (especially after January's F324 paper...)
that my friend, is AWESOME! you going for A* then? I wish you luck! Not that you need it of course, because you have brains.
12. (Original post by raj16)
do we have to know the manganate + iron, cu+I equations? also wen ur asked to draw a half cell wen do use a Pt electrode instead?

Thanks
Yeaaaah you do need to know those equations and i think you use a platinum electrode when you involve ions or non-metals. But when you have to investigate a solid, you use those rod things. I think?
13. Platinum electrodes are used when you have a mixture of two ions like Fe2+/Fe3+. Or when we are using non metals like hydrogen
14. (Original post by BA1)
Good luck to everyone anyway! I need 79/150 UMS for a grade A, which should equate to approx. 45-55 raw marks. I'm still revising a lot though, you never know what OCR will throw at us (especially after January's F324 paper...)
What are you doing to revise?? I've done all old past papers and the new ones as well read through my notes a couple of times as well
15. I don't understand how to work out the question at the end of the OCR unit 5 exam June 2010. 7b can someone please help?
16. (Original post by hellosarah)
Yeaaaah you do need to know those equations and i think you use a platinum electrode when you involve ions or non-metals. But when you have to investigate a solid, you use those rod things. I think?
surely all the half cells involve ions?
what about the Iodine + thiosulphate, and manganate + hydrogen peroixde??
17. Hey I have a question but don't have the mark scheme for it I have the correct answer but I have no idea how to get there using maths rather than just working it out trial and error:

a 167 mg sample of iron reacts with a stream of dry chlorine to form 487mg of solid X the molar mass of Solid X was determned to be 324.6 g mol-1

Calculate the molecular formula of X
that my friend, is AWESOME! you going for A* then? I wish you luck! Not that you need it of course, because you have brains.
I can't get an A*, I had 78/90 in F324 (which is just under 90%) and I'm not bothering to resit it as it clashes with my holiday dates end of next week :P I also did badly on the A2 practicals so had less than 90% in total for them. I just need a grade A for university so I'm not bothering to try and get the A*.

PS: That's why you should try and do well in the AS modules, to take the pressure off A2! I'm walking into an A2 maths exam next week needing 23/100 raw marks for a grade A, or 90/100 for an A* lmao!
19. How many raw marks would I need for 131 UMS going off past papers?
20. Do you think an essay question could be explain CO2 during ligand sub.?

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