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M.Chemistry Colours > Transition Metals > Flashcards

Transition Metals Flashcards

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1
Q

Why do transition metals form coloured solutions

A

Splitting of 3d orbitals

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2
Q

Explanation of splitting of D orbitals

A

Without ligands = all D orbitals have the same energy
- placing ligands around central ion causes splitting = some orbitals gain energy + some lose energy = produces 2 slightly different energy levels

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3
Q

How do we see light in transition metals

A

Electrons absorb energy equal to energy gap between 2 energy levels of D orbitals = electrons can be promoted (excited state)
- electrons absorb frequency of light with energy to jump energy gap
The coloured we see are a mix of the colours NOT absorbed = reflected light

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4
Q

What colour is a Cr 6+ oxidation state in alkaline conditions

A

Yellow

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5
Q

What colour is a Cr 6+ oxidation state in acidic condition

A

Orange

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6
Q

What can be used to reduce dichromate (6+) ions

A

Zinc in acid

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7
Q

What colour is a Cr 3+ ion

A

Dark green

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8
Q

What colour is a Cr 2+ ion

A

Blue

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9
Q

How do you oxidise a Cr3+ ion to Cr 6+ ion

A

H2O2 in alkaline conditions

1- Cr(H2O)6)3+ + NaOH = Cr(OH)6)3- +6H2O
Must convert into alkaline conditions = TMs in alkaline conditions + low Ox states are easier to remove electrons from = easier to remove E-s from negatively charged ions

2- add H2O2 (oxidising agent)
Cr(OH)6)3- = CrO4(2-)
+3 to +6

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10
Q

What chromate 6+ ion is yellow

A

CrO4(2-)
6+ in alkaline conditions

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11
Q

What chromate 6+ ion is orange

A

Cr2O7(2-)
Dichromate in acidic conditions

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12
Q

What colour is vanadium in 2+ oxidation state and what does the ion look like

A

V 2+
Violet

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13
Q

What colour is vanadium in 3+ oxidation state and what does the ion look like

A

V 3+

Green

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14
Q

What colour is vanadium in 4+ oxidation state and what does the ion look like

A

VO 2+

Blue

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15
Q

What colour is vanadium in 5+ oxidation state and what does the ion look like

A

VO2 +

Yellow

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16
Q

What reducing agent is used for all transition metals ( decreases oxidation state)

A

Zinc in acid

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17
Q

As the oxidation state gets larger in vanadium in the neumonic do you get close to the sun or lavender

A

Sun - yellow

V2+= Violet = lavender
V3+ = green = grass
VO 2+ = blue = sky
VO2 + = yellow = sun

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18
Q

How do you go from a chromate ion to a dichromate ion
CrO4 2- = Cr2O7 2-

A

1- boil to break down/ remove remaking H2O2 (hydrogen peroxide)

2- add acid/H+ ions= changes PH to acidic conditions
= yellow to orange

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19
Q

Why does the H2O2 need to be broken down before adding acid to form dichromate ions from chromate

A

Stop H2O2 reacting with the forming dichromate ions
Cr2O7 2-

20
Q

What colour is Cr3+ as a hexaqua ion / in solution with water

A

Cr(H2O)6)3+

Green solution

21
Q

What colour is Cr3+ as a hexaqua ion after reaction with NaOH

A

Cr(H2O)6)3+ + 3OH- = Cr(H2O)3(OH)3
Dark green precipitate

22
Q

What colour is Cr3+ as a hexaqua ion after reaction with Excess NaOH

A

Dark green solution
Cr(OH)6)3-

It’s soluable as it’s charged

23
Q

What colour is Fe 3+ as a hexaqua ion / in solution with water

A

Yellow

24
Q

What colour is a Fe3+ hexaquaion after reacting with NaOH

A

Brown precipitate

25
Q

What is the colour of a Fe2 hexaqua ion

A

Pale green

26
Q

What colour is the precipitate formed when Fe2+ hexaqua ion reacts with NaOH

A

Green precipitate

27
Q

What happens to the green precipitate of Fe(H2O)(OH)2 (Fe2+ ion) when standing

A

Oxidised by air
Fe2+ = to Fe3+
Goes from green to brown

28
Q

What colour is the hexaqua ion of Cu2+

A

Pale blue

29
Q

What colour is the pre update of Cu2+ after it reacts with NaOH

A

Blue precipitate

30
Q

What colour is the Co2+ hexaquaion in solution

A

Pink

31
Q

What colour is the Co2+ precipitate after hexaqua ion reacts with NaOH

A

Blue precipitate

32
Q

What happens to the Co(H2O)4(OH)2 when left standing

A

Co2+ oxidised to Co3+
Blue to brown

33
Q

Why are the reactions of NH3 and NaOH the same with hexaquaions when there not concentrated

A

Both act in acid-base reactions = O-H bond breaks on ligand of ion releasing it
The NH3 or OH- accept it

34
Q

Which hexaqua ions red-dissolve in excess NH3 out of:
Cu2+,Co2+, Fe2+
Cr3+, Fe3+

A

Both iron 2+ and 3+ do not
All the others do

35
Q

What colour forms when Co(H2O)4(OH)2 reacts in excess ammonia

A

Blue precipitate to brown
Blue = brown
Becomes Co(NH3)6) 2+

All 6 ligands replaced

36
Q

What colour forms when Cu(H2O)4(OH)2 reacts in excess ammonia

A

Blue precipitate to deep blue solution
Blue = deep blue

Cu(NH3)4(H2O)2 2+

Both OH- ligands replaced but only 2 of H2O ligands replaced

37
Q

What colour forms when Cr(H2O)3(OH)3 reacts in excess ammonia

A

Green precipitate to purple solution
Green = purple
Cr(NH3)6. 3+

All 6 ligands replaced by NH3

38
Q

What does acidity of hexaqua ions depend on

A

Ease to give up H+ ions in solution

Depends on size + Charge = higher the charge + smaller the Jon = the more polarising = weaken O-H bond more = more H+ in solution so more acidic

39
Q

Why are some comped ions colourless
(2 reasons)

A

1- not partially filled D orbitals = can be because they are full or empty
= no electrons can be promoted so no colour absorbed = all light is not absorbed so all light is reflected

2- energy gap so large = absorbs UV light = outside visible spectrum so appears colourless or white as solid

40
Q

Chelate effect of ligands

A

Multidentate ligands always replace monodentate ligands = more miles of molecule In product = increase in entropy

41
Q

Difference between mono and bidentate Ligands

A

Mono = can donate one lone pair of electrons

Bi = can donate 2 lone pairs of electrons

42
Q

Coordination number

A

Number of dative bonds in a complex NOT the number of ligands

43
Q

Definition of transition metal

A

D block elements that’s form one or more stable ions with partially/incompletely filled D orbitals

44
Q

How to name transition metal complexes

A

1- identify number of ligands = Di-2,
2- name the ligands = NH3 = amine
3- name central Ion = if ion is positive or neutral use metal name (copper)
- if negative charge = Latin name
4- add oxidation number to end

45
Q

Name this ion Ag(NH3)2. +1

A

Di- amine silver (1)

46
Q

Name this ion
Fe(CN)6. 3-

A

Hexa- cyano ferrate (3)

M.Chemistry Colours (4 decks)

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