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(Mod5): Cu2+ + NH3 ---> [Cu(NH3)4]2+ ammnia smll ligand thus shld be 6 not 4!?

Cu2+ + NH3 ---> [Cu(NH3)4]2+

It says in the AQA spec that:

"know that transition metals ions commonly form octahedral complexes with small ligands eg. H2O and NH3"

Therefore, ut should be 6, not 4, right?

Reply 1

EierVonSatan

It's actually [Cu(NH₃)₄(H₂O)₂]²⁺ :yep:

/not A-level

Reply 2

Waterstorm

Yeah, it's what EVS said.. it's Cu2+ in solution, and you do need to know that for AQA - deep blue colour. Damn I know these colours well! :wink:

So other equation you could write it as..

[Cu(H2O)6]2+ + 4NH3 --> [Cu(NH3)4(H2O)2]2+ + 4H2O

Reply 3

irfy

Waterstorm

Yeah, it's what EVS said.. it's Cu2+ in solution, and you do need to know that for AQA - deep blue colour. Damn I know these colours well! :wink:

So other equation you could write it as..

[Cu(H2O)6]2+ + 4NH3 --> [Cu(NH3)4(H2O)2]2+ + 4H2O

Is this Ligand Substitution, becuase you are replacing 4 H2O's with 4NH3's?

Reply 4

Nex Angelus

EierVonSatan

It's actually [Cu(NH₃)₄(H₂O)₂]²⁺ :yep:

/not A-level

im pretty sure it is A-level seen as how its in the syllabus.

Reply 5

EierVonSatan

Nex Angelus

im pretty sure it is A-level seen as how its in the syllabus.

but the reason why it's not Cu(NH₃)₆²⁺ isn't, I should have been clearer

Reply 6

Cryforhelp.

I failed this module spectacularly :gangster: Still got an A though :idea2:

Reply 7

EierVonSatan

Cryforhelp.

I failed this module spectacularly :gangster: Still got an A though :idea2:

then you didn't fail

Reply 8

Waterstorm

irfy

Is this Ligand Substitution, becuase you are replacing 4 H2O's with 4NH3's?

Yup, incomplete substition cause not all the ligands are replaced.

Another reaction to get that is when you're adding excess ammonia to copper hydroxide..

[Cu(H2O)4(OH)2] + 4NH3 --> [Cu(NH3)4(H2O)2] + 4H2O

That's from the reactions of inorganic compounds in aqueous solution section, where you reaction with NaOH, NH3 and Na2CO3 :smile:

Reply 9

Cryforhelp.

EierVonSatan

then you didn't fail

overall*

got a C in this module. Didn't know half the colours.

Reply 10

EierVonSatan

Cryforhelp.

overall*

got a C in this module. Didn't know half the colours.

Fair enough, I still don't know the colours

Reply 11

irfy

wait so does this exist:

[Cu(NH3)6]2+

?

Or does it only exist as (NH3)4(H2O)2 or (NH3)4(OH)2

Reply 12

Kyle_S-C

EierVonSatan

Fair enough, I still don't know the colours

Does anyone actually know the colours? They don't seem to be listed anywhere...

Reply 13

EierVonSatan

Kyle_S-C

Does anyone actually know the colours? They don't seem to be listed anywhere...

The question should be...why is it important to learn them off by heart?

I knew them for my A-levels and quickly forgot them soon after.

Reply 14

Waterstorm

irfy

wait so does this exist:

[Cu(NH3)6]2+

?

Or does it only exist as (NH3)4(H2O)2 or (NH3)4(OH)2

Yeah it does, but you don't need to know it for A level.. don't worry about it. Just know Co2+, Co3+ and Cr3+ with 6 NH3 ligands.

Reply 15

EierVonSatan

irfy

wait so does this exist:

[Cu(NH3)6]2+

?

Or does it only exist as (NH3)4(H2O)2 or (NH3)4(OH)2

It does exist but it's much harder to form, just know the above reaction where it substitutes 4 ligands.

Reply 16

Kyle_S-C

EierVonSatan

The question should be...why is it important to learn them off by heart?

I knew them for my A-levels and quickly forgot them soon after.

So you know if you made the right thing for your part II practical. :p:

Spectroscopy is overrated, colour ftw! :biggrin:

Reply 17

ClaireHogben

I hate this module with a passion, and am really starting to panic about it now

Reply 18

Kyle_S-C

ClaireHogben

I hate this module with a passion, and am really starting to panic about it now

Don't worry too much, do you have any UMS marks going spare? People often end up finding that they could afford really low marks in one or two papers because of their ASs and a solid performance in paper 4.

If it comes down to it, just bung the colours down on a flash card and have a look at it whilst you're waiting outside the exam hall. Don't forget to leave it outside though.