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Transition Metal Colours

2

Where is everyone learning their transition metal colours from? Does anyone have that Heinemann AQA Chem A2 revision book? Would anyone be able to scan in that page with the trans.colours on for addition w/Na2CO3, NH3 and HCl, that's all of the reactants...I think? I would really appreciate it! I have a colour chart from my teacher and one in the book but they are both different to the mark scheme! argh if anyone has a colour scheme that is compatible with the AQA mark schemes i would be really grateful, cos I don't know which are the right colours! p.s. is CuCO3 blue or green?? Thanks! :rolleyes:

Reply 1

noggin

7

Cu2+ = pale blue gelatinous ppte with NaOH
Fe2+ = green " " "
Fe3+ = rusty orange " " "
[Cu(NH3)4(H2O)2]2+ = royal blue
[CuCl4]2- = yellow
[Cu(H2O)6]2+ = pale blue
[Fe(SCN)(H2O)5]2+ = blood red
[Fe(H2O)6]3+ = yellowy brown

i'm doing OCR and these are all we need to know, but dont know about AQA sorry. have you checked the syllabus?

Reply 2

Asphyxiating

OP

2

I have CuCl(4)(2-) as green, [Fe(H20)6]3+ as yellow/orange :frown:

Hm well AQA syllabus just says colours of complexes in this module..but I think it's

colour of
all the vanadium ox.states,
chromate,dichromate
iron(II), iron (III), cobalt, aluminium, copper, chromium aqeous reactions w/Na(2)CO(3), HCl, NH3, NaOH & colours in excess
silver reactions w/thio, NaOH and NH3

anyone got anymore we need?

Reply 3

Asphyxiating

OP

2

Ok can someone just confirm this:

CuCO(3) = blue or green?
[Cr(H2O)6]3+ + conc. HCl ---> [CrCl(6)]3- or [CrO(4)]2- (then [Cr(2)O(7)]2-) ?

Thanks :biggrin:

Reply 4

ShOcKzZ

7

Asphyxiating

Ok can someone just confirm this:

CuCO(3) = blue or green?
[Cr(H2O)6]3+ + conc. HCl ---> [CrCl(6)]3- or [CrO(4)]2- (then [Cr(2)O(7)]2-) ?

Thanks :biggrin:

CuCO3 is a 'blue-green' ppt not 'blue or green'

not sure about the second..never come accross it. shud i be worried? lol.

Reply 5

selkie222

3

Definitely not [CrO(4)]2-

You will need to put [Cr(H2O)6]3+ with H2O2 and OH- to do that.

I think [CrCl(6)]3- is also green...?

Reply 6

Asphyxiating

OP

2

selkie222

Definitely not [CrO(4)]2-

You will need to put [Cr(H2O)6]3+ with H2O2 and OH- to do that.

I think [CrCl(6)]3- is also green...?

Ok so it makes [CrCl(6)]3-?
Is [Fe(H20)(6)]3+ yellow or brown?

Thanks v much :biggrin:

p.s. yes [CrCl(6)]3- is green

Reply 7

Asphyxiating

OP

2

ShOcKzZ

CuCO3 is a 'blue-green' ppt not 'blue or green'

not sure about the second..never come accross it. shud i be worried? lol.

hm argh so i have blue and green and blue-green, I take it it's close then so they might accept any of those answers? Did it say blue-green in the mark scheme of a past paper somewhere?

Reply 8

ShOcKzZ

7

Asphyxiating

Ok so it makes [CrCl(6)]3-?
Is [Fe(H20)(6)]3+ yellow or brown?

Thanks v much :biggrin:

p.s. yes [CrCl(6)]3- is green

where are you getting these complexes from..ive just got:

[Fe(H2O)6]2+
[Co(H2O)6]2+
[Cu(H2O)6]2+

[Fe(H2O)6]3+
[Al(H2O)6]3+
[Cr(H2O)6]3+

with ..OH- (little), OH- (excess) NH3 (little) NH3 (excess) and Carbonate..

where do all the Cl's come into it?? :confused:

Reply 9

selkie222

3

Actually not sure if it makes anything... [CrCl(6)]3- sounds like a reasonable choice between the two but you'll need quite concentrated HCl since Cl- is a weaker ligand than H2O.

In my notes there is a partially cholosubstituted species [CrCl(2)H2O(4)]+ which sounds more possible.

In the module book (I think... just checked, yes) it says that [Fe(H2O)(6)]3+ is a (scary!) pale violet(!!!) but appears yellow due to hydrolysis.

It is brown when precipitated as [Fe(H2O)(3)(OH)(3)]

Mark schemes are usually somewhat flexible on these points, I understand.

I might have seen a pale violet iron(III) crystal once, but I have never seen it pale violet in solution.

selkie

Reply 10

selkie222

3

ShOcKzZ

where are you getting these complexes from..ive just got:

[Fe(H2O)6]2+
[Co(H2O)6]2+
[Cu(H2O)6]2+

[Fe(H2O)6]3+
[Al(H2O)6]3+
[Cr(H2O)6]3+

with ..OH- (little), OH- (excess) NH3 (little) NH3 (excess) and Carbonate..

where do all the Cl's come into it?? :confused:

Vanadium?

Yes all those above are pretty much what you need. But for several random ones--- Co, Cu they do expect you to know the colour of the tetrachloro ion.

[CoCl4]2- is blue
[CuCl4]2- is yellow-green (interesting little equilibrium, because if you add more water, it goes back to blue due to H2O being a stronger ligand)

Apart from those, you might have some di-substituted chloro ions ith Cr(III) and V(III), for which a good guess is green.

And by the way anhydrous CoCl2 is blue--- it is part of a test for water (blue to pink)

That's all I think...

selkie

Reply 11

Asphyxiating

OP

2

selkie222

Vanadium?

Yes all those above are pretty much what you need. But for several random ones--- Co, Cu they do expect you to know the colour of the tetrachloro ion.

[CoCl4]2- is blue
[CuCl4]2- is yellow-green (interesting little equilibrium, because if you add more water, it goes back to blue due to H2O being a stronger ligand)

Apart from those, you might have some di-substituted chloro ions ith Cr(III) and V(III), for which a good guess is green.

And by the way anhydrous CoCl2 is blue--- it is part of a test for water (blue to pink)

That's all I think...

selkie

Thanks, yeap I'm getting there now, slowly! Thanks so much, you've been a real help :tongue:

Reply 12

Asphyxiating

OP

2

Ok one more.. :tongue:

When you add excess NaOH to [Cr(H2O)6]3+ do you get [Cr(OH)6]3- which is dark green soln or do you get [Cr(OH)4(H2O)2]- which is a green soln?

Also do we need to know that Co(H2O)4(OH)2 stands in air to become oxidised to beige ppt Co(OH)3 ?

Ok think i'm alright now thanks :smile:

Reply 13

kingpong

Where are all these 6 Cl- ligand complexes from?!?!

I was under the impression Cl- could only form 4 ligands due to size/charge etc.???

Reply 14

selkie222

3

kingpong

Where are all these 6 Cl- ligand complexes from?!?!

I was under the impression Cl- could only form 2 ligands due to size/charge etc.???

Good point. Yes 6 Cl- ligand complexes probably won't happen (not to the metals we are studying anyways), but 4 Cl- complexes do happen to Cu and Co (which is yellow green and blue respectively).

Asphyxiating

When you add excess NaOH to [Cr(H2O)6]3+ do you get [Cr(OH)6]3- which is dark green soln or do you get [Cr(OH)4(H2O)2]- which is a green soln?

It seems to be possible for [Cr(OH)6]3- to get to 6OH-, partly maybe because OH- is a strong ligand... but there are reasons to do with chromium too, which we don't need to know.

I think the most important thing to know with [Cr(H2O)6]3+ is that it forms green ppt on adding a little base, and it dissolves on excess OH- to form a green solution.

And again [Cr(H2O)6]3+ is a (startling) "red-violet" or "ruby red" according to the module books--- however it appears green due to hydrolysis (which is what I usually see!)

selkie

Reply 15

Asphyxiating

OP

2

selkie222

It seems to be possible for [Cr(OH)6]3- to get to 6OH-, partly maybe because OH- is a strong ligand... but there are reasons to do with chromium too, which we don't need to know.

I think the most important thing to know with [Cr(H2O)6]3+ is that it forms green ppt on adding a little base, and it dissolves on excess OH- to form a green solution.
selkie

Reply 16

T.r.i.n.i.t.y

I HAVENT EVEN LEARNT THOSE COLOURS YET!!, i am so going to fail 2moro

Reply 17

DaveR

Here are all the transition colours I know

[V(H2O)6]2+ = purple
[V(H20)6]3+ = green
[VO]2+ = blue
[VO2]+ = yellow

[Cr(H20)6]3+ = green
[Cr2O7]2- = orange
[CrO4]2- = yellow

[Mn(H2O)6]2+ = pale pink
[MnO4]- = purple

[Fe(H2O)6]2+ = green
[Fe(H2O)6]3+ = orange/brown

[Cu(H2O)6]+ = colourless
[Cu(H2O)6]2+ = blue
[Cu(NH3)4]2+ = deep blue

Hope that helps.

Reply 18

Barny

17

Since when do we have to know the colours?