OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

[Cr(H2O)6]2+

:-)

I think a general rule of thumb is that a metal ion in water has 6 water ligands

I really hate those buffer questions.

What is A? thanks

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[Cr(H2O)6]3+

:-)

I think a general rule of thumb is that a metal ion in water has 6 water ligands

Sorry that was a 3+

CrCl₃.6H₂O

I'll edit in a spoiler with all the answers in the OP

Wasn't the solution green though? Chromium in water is blue in solution and green with a chloride ligand. Or am I majorly wrong


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I don't think we're expected to know the colours of chromium ions (except that it goes from orange to green in oxidation reactions) hence why they gave us so many hints with anion etc etc

However, Cr in the +3 oxidation state and aqueous is indeed green. It is blue in the +2 state (quick google search shows this)

Cr 3+ is technically violet, it's just that almost every reaction you would ever do with it involves some ligand exchange hence the green

Yep I was just about to add that


http://www.chemguide.co.uk/inorganic/transition/chromium.html

More or less than you hate plants? :P

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yep I suspect it is a classic example of chemguide going well beyond what you need to know but oh well

So just getting things clear. It should be violet in aqueous solution without other ligands such as chloride ions but for the sake of the spec we say it's green? But really it's only green with, for example, 2 chloride ions acting as ligands?


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f324/f325 predictions guys? :P

ez a*

f324/f325 topic predictions guys? :P

This reaction is happening:

HCOO- + H+ > HCOOH
When the salt reacts with H+, more acid is produced
Hence when the moles of salt decreases by 5x10^-4, the moles of acid increases by the same amount

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40 marks on mechanisms F324