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!
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Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch
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KnuckleheadNinja
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- 1101
- 14-06-2011 16:38
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CoventryCity
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- 14-06-2011 16:39
(Original post by student777)
But surely you can just get that from oxidation numbers? Eg if it's Cl- it has oxisation state -1
And what about this question, from june 2010 question 2:
BrO3- + ....Br- + ....H+ --> ....Br2 + ....H2O
There aren't any charges on the RHS? -
CoventryCity
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- 14-06-2011 16:39
(Original post by KnuckleheadNinja)
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!
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- 1104
- 14-06-2011 16:40
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 ??
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KnuckleheadNinja
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- 1105
- 14-06-2011 16:41
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- 1106
- 14-06-2011 16:41
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 -
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- 1107
- 14-06-2011 16:45
(Original post by student777)
But surely you can just get that from oxidation numbers? Eg if it's Cl- it has oxisation state -1
And what about this question, from june 2010 question 2:
BrO3- + ....Br- + ....H+ --> ....Br2 + ....H2O
There aren't any charges on the RHS?
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? -
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- 1108
- 14-06-2011 16:46
(Original post by KnuckleheadNinja)
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
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...) -
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- 14-06-2011 16:47
edit: -ve??? what did i do wrong???Last edited by monkeyDace; 14-06-2011 at 21:24. -
CoventryCity
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- 14-06-2011 16:48
(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 ??
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 -
KnuckleheadNinja
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- 1111
- 14-06-2011 16:48
(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...) -
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- 1112
- 14-06-2011 16:49
(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?
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CoventryCity
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- 1113
- 14-06-2011 16:51
Platinum electrodes are used when you have a mixture of two ions like Fe2+/Fe3+. Or when we are using non metals like hydrogen
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sportycricketer
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- 1114
- 14-06-2011 16:53
(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...)read through my notes a couple of times as well
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Medifield
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- 1115
- 14-06-2011 16:53
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?
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- 1116
- 14-06-2011 16:55
(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?
what about the Iodine + thiosulphate, and manganate + hydrogen peroixde?? -
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- 1117
- 14-06-2011 16:58
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 -
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- 1118
- 14-06-2011 16:58
(Original post by KnuckleheadNinja)
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.
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!Last edited by BA1; 14-06-2011 at 16:59. -
CoventryCity
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- 14-06-2011 16:58
How many raw marks would I need for 131 UMS going off past papers?
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CoffeeStinks
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- 14-06-2011 16:58
Do you think an essay question could be explain CO2 during ligand sub.?
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