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ocr a f325 revision thread

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Original post by A-New-Start
What ways can you make a buffer?

adding naoh, ammonia ?


Acid in excess + a base :smile:
Reply 3161
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shepan6
Good Luck everybody, I hope they don't pull a Jan 2013 on us!!!! :biggrin:
Original post by DudeBoy
[Cu(H2O)2(NH3)4]+2


Thanks

Also does anyone know the difference between tetrahedral and square planar?
Original post by Myocardium
Thanks

Also does anyone know the difference between tetrahedral and square planar?


Square planar 90
Tetrahedral 109.5
For the most part the only square planar we need to know is Platin
Reply 3164
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XiLE
Can someone please explain question c.ii) on June 2012?
http://www.ocr.org.uk/Images/131289-question-paper-unit-f325-equilibria-energetics-and-elements.pdf
I keep getting 4.12. :/
Answer is 4.22.
Original post by alltimeemilyxo
oh thankyou thats a good way to remember it!


That's ok, I have to find small tricks otherwise I get confused

Good luck! :smile:
Original post by DudeBoy
It's ok :smile: This helps me revise too.

You always need to scale because by definition "The enthalphy change of neutralisation is the enthalpy change that occurs when an acid and a base react fully to form 1 mol of water"
So always scale to 1 mole :smile:


okay! so the only time you wouldn't need to is if you have 1 mole of acid/base?


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Reply 3167
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kuku2013
do you think redox titrations will come up?
Anyone have a list of all the colours we need to know?
Original post by georgiaaaxo
okay! so the only time you wouldn't need to is if you have 1 mole of acid/base?


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Yep :smile:
Otrivine, what you asked about standard enthalpy change of formation being endothermic...it isn't. Bonds formed.
Original post by AyshaK
i mean with the equal vol of water added


Got it thanks


Do u know why enthlpy change of formation is endothermic
so worried. a lot is resting on this exam for me :frown: hope it's a kind paper!


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Original post by DudeBoy
Yep :smile:


great! thankyou so much :smile:


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Reply 3174
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meg0001
Do you ned to memorise MnO4- and I2/S2O3^2- equations or will they be given in the exam?
Reply 3175
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XiLE
Original post by XiLE
Can someone please explain question c.ii) on June 2012?
http://www.ocr.org.uk/Images/131289-question-paper-unit-f325-equilibria-energetics-and-elements.pdf
I keep getting 4.12. :/
Answer is 4.22.


Bump
Reply 3176
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chiny94
8
Quick question, what's the bond angle of square planar? And [CuCl4]2- is tetrahedral right?

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Original post by AyshaK
equal volumes of water are added but conc stays the same so the overall volume doubles and if they're asking for conc in the overall volume you'll half the conc if that makes sense?


Which paper had this question
Original post by A-New-Start
Anyone have a list of all the colours we need to know?


Fe3+ + 3OH- --> Fe(OH)3 (Pale yellow to rusty brown ppt)
Fe2+ + 2OH- --> Fe(OH)2 (Pale green to green ppt)
Cu2+ + 2OH- --> Cu(OH)2 (Blue to blue ppt)
Co2+ + 2OH- --> Co(OH)2 (Pink to blue ppt)

[Cu(H2O)6]+2 + 4NH3 ---> [Cu(H2O)2(NH3)4]+2 + 4H2O (Blue solution to dark blue solution)
[Cu(H2O)6]+2 +4Cl- ---> [CuCl4]-2 + 6H2O (Blue solution to yellow solution)
[Co(H2O)6]+2 +4Cl- ---> [CoCl4]-2 + 6H2O (Pink solution to blue solution)
Original post by otrivine
Got it thanks


Do u know why enthlpy change of formation is endothermic


It isn't. It's exothermic because bonds are made.

I just think 'BMX'

Bonds Made EXothermic

Otherwise I get confused haha.

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