Unit5/unit 4 chemistry - EDEXCEL June 2012
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012thanks so much(Original post by iesians)
didnt you guys learn this stuff ..?!?!
well, left half cell has ZnSO4 so the elctrode has to be of Zn of course (def of a half cell is an electrode dissolved in the solution of its own ions) !!
in the right half cell we have a mixture of ions Fe2+ and Fe3+ so we WONT use Fe electrode we will use a platinum electrode
REMEMBER THIS IN MIND whenever there's a mixture of ions we will always use PLATINUM electrode !
and if there is only one ion then we wil use the electrode of its element !
Can you explain to me the amphoteric behaviour of oxides please? -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012there are only two oxides (hydroxides) which posess amphoteric nature(Original post by aqua05)
thanks so much
Can you explain to me the amphoteric behaviour of oxides please?
Cr(OH)3 and Zn(OH)2
theyll react with bases (NaOH) to form Cr(OH)6^-3 and Zn(OH)4^-2 respectively
and theyll also react wiht acids (HCl) to form the aqeous ion again :-
Cr(H2O)6^3+ and Zn(H2O)4^2+ !! -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012thanks so much(Original post by iesians)
there are only two oxides (hydroxides) which posess amphoteric nature
Cr(OH)3 and Zn(OH)2
theyll react with bases (NaOH) to form Cr(OH)6^-3 and Zn(OH)4^-2 respectively
and theyll also react wiht acids (HCl) to form the aqeous ion again :-
Cr(H2O)6^3+ and Zn(H2O)4^2+ !!
And what about errors? -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012AAAAAAAAAAAAAAAAAA OMFGEEEEEE how are yaa ! i missed ya like helllllll !!!!!!!!!!!!!!!!!!!! (sobs) ! anyway yeah ikr im so happy too cuz of that lol(Original post by totally lost)
Any predictions guys? Thnk gosh tmrws paper is in the afternoon got the morning to revise! 
im thinking iodometry titration will come cuz it didnt come in jan ! -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012Hahah i misssed u toooooo!(Original post by iesians)
AAAAAAAAAAAAAAAAAA OMFGEEEEEE how are yaa ! i missed ya like helllllll !!!!!!!!!!!!!!!!!!!! (sobs) ! anyway yeah ikr im so happy too cuz of that lol
im thinking iodometry titration will come cuz it didnt come in jan ! i left u a message have u seen it? Serious idometric? I gotta revise that 0.0 ..! 
Last edited by totally lost; 18-06-2012 at 22:05. -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012Multiply by 2 when you are taking 2 readings...(Original post by aqua05)
hey guys
can someone go over errors with me? when are we suppose to multiply by 2?
Errors for volume, temperature, and mass? pleasee!
in a burete you take initial reading then end reading
however in a pipette you take one reading, which the initial one -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012Best one to use for this is thin layer chromatography (TLC)(Original post by nazeeb)
can someone please give me the answer for the question no.23 (b) of jan 12 unit 5 chem!!! please please please!! i really need it as i barely understand the chromatography part of unit 5
-Dissolve the amino acids in a suitable solvent, and place a spot of them on a plastic plate covered in silica gel (stationary phase). Also put spots of known amino acids on there aswell
-Dip plate in the eluent (mobile phase) and it will move up the plate by capillary action. How far they go up depends on the relationship between the amino acid, and the mobile and stationary phase
- spray the plate with ninhydrin and heat. The amino acids will turn a dark purple colour
-then you can compare your amino acids with the known samples that you put on the plate
Im sure theres some mistakes there but thats the best i can do! -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012You're right it should be Zn(H2O)4(OH)2, i think a couple of books made a mistake with this.(Original post by im so fresh)
Really quick question
For: [Zn(H2O)6]2+ ~with OH-/NH3 it goes to Zn(H2O)3(OH)3 (s)
i thought because it was initially a 2+ charge it would go to Zn(H2O)4(OH)2 (s)???? -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012thx(Original post by oHellno)
You're right it should be Zn(H2O)4(OH)2, i think a couple of books made a mistake with this.
Good luck! -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012haha sounds good...(Original post by James A)
yo dude, forgot to ask about how your unit 4 exam for chem went?
Mine went superbly !!
estimated around 79-78/90 marks so I should need roughly a B on unit 5 for my A overall.
Hows your revision for chem 5 going?
honestly - i have no idea hahaha
probably did badly know me
lol
=/ -
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Re: Unit5/unit 4 chemistry - EDEXCEL June 2012at last a mind which thinks alike(Original post by im so fresh)
oh i'm going to miss chemistry :/ as annoying as chem was, it sill was a lot of fun
Last edited by King_Arthur; 21-06-2012 at 05:45.
that's how it's shown in the George Facer book.
