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AQA CHEM5 A2 Chemistry - 19th June 2013

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Original post by Anshul91
Al(H2O)6 3+ in excess OH is it Al(OH)4 - OR Al(OH)6 3- ???? THANKS


[Al(OH)4(h20)2]-


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Original post by RoaringLion
[Al(OH)4(h20)2]-


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PI thought the same but one markscheme says aloh6 3-
pthough accept both
Reply 2282
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popnit
14
Original post by Anshul91
Al(H2O)6 3+ in excess OH is it Al(OH)4 - OR Al(OH)6 3- ???? THANKS


I've got [Al(OH)4]- colourless solution for xs OH

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Wats the full equation for mno4- and c2o42-

i got the half equations
Reply 2284
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Anshul91
Original post by popnit
I've got [Al(OH)4]- colourless solution for xs OH

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ah so whats the overall equation for excess naoh with aq aluminium please??
Reply 2285
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lmon
5
I can't sleep :frown:
Original post by Anshul91
ah so whats the overall equation for excess naoh with aq aluminium please??


Al(h20)6 3+ + 4OH- = al(oh)4- + 6h20
Do you only need to put state symbols when it asks for them ??
Reply 2288
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Anshul91
what times the exam?
Reply 2289
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indyb16
5
Original post by SexyAndIKnowIt.
Do you only need to put state symbols when it asks for them ??


yeah if you put them and they're wrong and they didn't ask you get penalised


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Good luck!! :smile:
Original post by A sheesh
Lets just hope it's not a bull paper like June 12...
that paper annoyed me so much, no matter what I did I got 0.1 for the gradient!



also how is the ratio 3:5 can someone explain?


well the deltaG scale was in kJmol^-1, if you converted it into Jmol^-1 you would get the gradient of 98-100 although they accepted 0.1 providing you put kJ K^-1 Mol^-1.

The ratio one was where you had to recognise the FeC2O4 had two seperate partial equations that made up their half equation. Fe2+ --> Fe3+ + e- and C2042- --> 2CO2 + 2e- which combine to form the half equation Fe2+ + C2O42- --> Fe3+ + 2CO2 + 3e- (or FeC2O4 --> Fe3+ + 2CO2 + 3e-)

the MnO4- was MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O

so when you combine the equations it becomes 3x the MnO4 reduction half equation and 5x the FeC2O4 oxidation half equation:

3MnO4- + 24H+ + 5FeC2O4 --> 5Fe3+ + 10CO2 + 3Mn2+ 12H2O
(edited 10 years ago)
Reply 2292
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wadz
2
Morning exam so 9am.

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Original post by Anshul91
what times the exam?


Morning = 9am :cool:
Original post by A sheesh
Wats the full equation for mno4- and c2o42-

i got the half equations


2MnO4- + 16H+ + 5C2O42- --> 2Mn2+ + 8H2O + 10CO2
Reply 2295
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hilo36
Good luck everyone!!! xxx
Reply 2296
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Anjna
9
why do transition metals show colour?
Original post by Anjna
why do transition metals show colour?


partially full d orbitals.
Original post by Anjna
why do transition metals show colour?


The exam is in an hour and a half. I know I'll get negged for this but how do you not know that?

It's because the d orbital splits so light is absorbed when electrons are excited to the higher level
Well, here goes nothing :frown:


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