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Aqa chem 4/ chem 5 june 2016 thread

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What colour is
[Cr(NH3)6]3+


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why topics from AS are you guys looking back at?
Original post by Kikstar
Thank you so much! I can now sleep in peace haha. Best of luck in your exams :smile:


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No worries! Good luck to you too :smile:
Original post by Bloom77
What colour is
[Cr(NH3)6]3+


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Purple
Cobalt with excess OH-: [Co(H2O)6)2+ + 2OH- --> Co(H2O)4(OH)2 + 2H20
Reply 2185
how do you suss out which species to use as the salt bridge of a cell
Original post by Boundless_x
What about if they ask for [Al(H20)6]2+ with excess OH?


[Al(H2O)6]3+ + 6OH- ===> [Al(OH)6]3- + 6H2O
Original post by SirRaza97
[Al(H2O)6]3++ 4OH- ===> [Al(OH)4] - + 6H2O

it's aliminium 3+ not 2+


Thanks :smile:
Ahh yeah it is...I'm so tired that I've forgotten how to distinguish between different numbers :s-smilie:
Can always use KNO3 in the salt bridge?
Original post by GO97
how do you suss out which species to use as the salt bridge of a cell


I usually go for KNO3 but just make sure that the salt bridge won't react with the reagents on either side.
Original post by Hopefulmedic15
[Al(H2O)6]3+ + 6OH- ===> [Al(OH)6]3- + 6H2O


I've seen this one in pastpapers
Original post by SirRaza97
[Al(H2O)6]3++ 4OH- ===> [Al(OH)4] - + 6H2O

it's aliminium 3+ not 2+


This one is in my notes...

Which one are we supposed to use?
Original post by Boundless_x
Thanks :smile:
Ahh yeah it is...I'm so tired that I've forgotten how to distinguish between different numbers :s-smilie:


It won't only be 4OH- if it's in excess!

EDIT scratch that the book says it would be 4OH-

2nd edit, I also thought I saw it with 6 in past papers, so I don't know tbh

3rd edit, just found this on the AQA chem 5 page for wiki books and it says it goes to [Al(OH)6]3- in excess OH- but tbh, both would form a colourless solution
(edited 7 years ago)
Original post by study2016
Guys - if you would recommend I do any 3 CHEM5 papers, which ones would they be? Very short for time - hectic exam timetable :s-smilie:


I found June 2012 pretty hard
Best of luck for tomorrow everyone!! lets smash this exam! ( to make up for chem 4 haha!)
Original post by ChlorophyllA
Cobalt with excess OH-: [Co(H2O)6)2+ + 2OH- --> Co(H2O)4(OH)2 + 2H20


isnt this also the equation with little hydroxide
Does anyone know the general method of calculation when you have to use the specific heat capacity of water and the mass of something?
Original post by Boundless_x
I've seen this one in pastpapers


This one is in my notes...

Which one are we supposed to use?


I've got a different one...
I have:

Al(H2O)3(OH)3 + OH- --> [Al(H2O)2(OH)4]- + H2O

..... :/


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Original post by Hopefulmedic15
I usually go for KNO3 but just make sure that the salt bridge won't react with the reagents on either side.


what else apart from potassium nitrate can you use?
Original post by Lilly1234567890
isnt this also the equation with little hydroxide


The 2+ ions don't actually react with excess NaOH, only excess NH3. They react with limited NaOH to give [M(H2O)4(OH)2] :smile:
Original post by werdo1997
The 2+ ions don't actually react with excess NaOH, only excess NH3. They react with limited NaOH to give [M(H2O)4(OH)2] :smile:


yeah that what i meant- as when the +2 metal reacts with little hydroxide isnt that^ the equation we use?

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