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module 6 aromatic test > Chapter 24 - Transition Elements > Flashcards

Chapter 24 - Transition Elements Flashcards

1
Q

What is the role of cis-platin in medicine

A

It is an anticancer drug and it does this by binding to DNA preventing cell division

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2
Q

What is a ligand-substitution reaction?

A

A reaction where one one ligand in a complex ion is replaced by another ligand

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3
Q

When copper(II) sulfate is dissolved in water what complex is formed and what colour is this?

A

[Cu(H2O)6]2+ is formed in aqueous solution and it is pale blue

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4
Q

What is formed when aqueous ammonia is added dropwise to [Cu(H2O)6]2+ ?
What is the colour change?
Describe this reaction

A

Starts as a pale blue solution, then a pale blue ppt is formed - Cu(OH)2 and then a dark blue solution is formed - [Cu(NH3)4(H2O)2]2+ (aq)

In this reaction four of the water ligands are replaced by four of the ammonia ligands

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5
Q

What is formed when hydrochloride acid is added to [Cu(H2O)6]2+ ?
What is the colour change?
Describe this reaction

A

Original solution is pale blue but [CuCl4]2- is yellow. However a reversible reaction means the reaction mixture is green

Six water ligands have been replaced by four chloride ligands

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6
Q

What complex is formed when chromium is dissolved in water and what is the colour of the solution?

A

[Cr(H2O)6]3+ and this is a pale purple solution

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7
Q

What happens when ammonia is added dropwise to [Cr(H2O)6]3+?

A

1) Initially a grey-green ppt is formed of Cr(OH)3

2) The Cr(OH)3 ppt dissolves in excess ammonia to form the complex ion to form [Cr(NH3)6]3+ (a purple solution)

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8
Q

Why is the iron in haemoglobin so important?

A

The central metal ion in a haem group, Fe2+, can bind to oxygen and carry it round the body

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9
Q

Describe ligand substitution of haemoglobin

A

In the lungs the haemoglobin can bond to oxygen, forming oxyhaemoglobin which release oxygen to body cells when required

If CO is breathed in a ligand substitution can take place where oxygen is replaced by carbon monoxide and carbon monoxide bonds more strongly than oxygen (prevents haemoglobin from carrying oxygen)

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10
Q

What colour changes take place when aqueous Cu2+, Fe2+, Fe3+ and Mn2+ are reacted with aqueous sodium hydroxide?

A

Cu2+ : Blue solution reacts to form blue ppt
Fe2+ : Pale green solution reacts to form a green ppt
Fe3+ : Pale yellow solution reacts to form an orange-brown ppt
Mn2+ : Pale pink solution reacts to form a light brown ppt

All insoluble in excess NaOH

E.g Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)

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11
Q

What happens when Mn(OH)2 and Fe(OH)2 are left to stand in air?

A

Mn(OH)2 : light brown ppt darkens

Fe(OH)2 : green ppt gets brown on surface as iron(II) is oxidised to iron (III)

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12
Q

What happens when sodium hydroxide is added to Cr3+ ions?

A

Violet solution reacts to form a grey-green ppt - Cr(OH)3

Ppt is soluble in excess of sodium hydroxide forming a dark green solution [Cr(OH)6]3-

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13
Q

Precipitation reactions of Cu2+, Fe2+, Fe3+, Mn2+ and Cr3+ with ammonia?

A

Cu2+ : Cu(OH)2 dissolves in excess ammonia to form [Cu(NH3)4(H2O)2]2+
Fe2+ : Fe(OH)2 - (react the same way as with sodium hydroxide)
Fe3+ : Fe(OH)3
Mn2+ : M(OH)2
Cr3+ : Cr(OH)3 dissolves in excess ammonia to form [Cr(NH3)6]3+

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14
Q

Colour changed with reduction of acidified Cr2O7(2-)

A
  • Cr2O7(2-) is orange
  • When acidified Cr2O7(2-) is added to zinc this produces Cr3+ which are green
  • With an excess of zinc Cr3+ can be reduced further to Cr2+ which is a pale blue colour
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15
Q

Reduction of Cu2+ to Cu+ (by iodide)

A

When Cu2+ reacts with excess iodide ions, the Cu2+ forms a white ppt of copper(I) iodide and the iodine formed is brown.

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16
Q

Disproportionation of Cu+ ions (by sulphuric acid)

A

Cu2O(s) + H2SO4(aq) -> Cu(s) + CuSO4(aq) + H2O(l)

Brown ppt of copper and blue solution of copper sulfate. Cu+ has been oxidised and reduced

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17
Q

Reduction of Fe3+ to Fe2+ (by iodide)

A

2Fe3+ + 2I- –> 2Fe2+ + I2

When a solution of Fe3+ reacts with iodide ions, the Fe3+ ions are deduced to pale green Fe2+ but this is masked by the production of brown iodine

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18
Q

what is a -d block element?

A

elements with their highest energy electron I=in a -d sub-shell
they are metals, able to form complex ions

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19
Q

notes to remember for electron configuration of d block metals/ions

A

the 4S subs hell fills and empties before the 3d subs hell

20
Q

electron configuration of chromium (doesn’t follow rules)

A

[Ar] 3d5 4s1

21
Q

electron configuration of copper (doesn’t follow rules)

A

[Ar] 3d10 4s1

22
Q

why don’t chromium and copper follow the usual rules of electron configuration?

A

stability.
It is believed that the half filled d5 sub-shell and the fully filled 610 sub-shell give additional stability to the atoms of chromium and copper.

23
Q

what is a transition metal?

A

a d block element that forms at least one ion with a partially filled d orbital.

24
Q

which d block elements are not classed as transition metals and why

A

zinc and scandium.

Zn 2+ and Sc 3+ do not have partially filled d orbitals.

25
Q

properties of transition metals and their compounds

A
  • form compounds where the transition metal can have different oxidation states
  • form coloured compounds (different oxidation states have different colours)
  • elements and compounds act as good catalysts
26
Q

how to tell if a transition metal compound will be a good oxidising agent?

A

if the compound contains its transition metal in its highest oxidation state it is often a strong oxidising agent

27
Q

iron colours (different oxidation states)

A

Fe +2 = pale green

Fe +3 = yellow

28
Q

chromium colours (different oxidation states)

A

Cr +3 = green (acidified with sulfuric acid)

Cr +6 = orange (or yellow)

29
Q

manganese colours (different oxidation states)

A

Mn +2 = very pale pink

Mn +7 = purple

30
Q

examples of transition metals as heterogeneous catalysts

A
  • MnO2 for decomposition of H2O2

- Fe for Haber process

31
Q

when is a complex ion formed

A

a complex ion is formed when one or more ligand makes coordinate bonds to a central metal atom.

32
Q

what is a ligand

A

a molecule or ion that donates a lone pair of electrons to a central metal ion to form a special kind of dative covalent bond called a coordinate bond

33
Q

whats tells you how many coordinate bonds are being made with the central metal ion in a complex ion

A

the coordination number

34
Q

representing complex ions

A
  • whole ion enclosed in square brackets
  • ligand inside round brackets
  • overall charge outside brackets (charge of metal ion + any ligands)
    eg [Cr(H2O)6] 3+
35
Q

define a monodentate ligand

A

able to donate one pair of electrons to a central metal ion

36
Q

common monodentate ligands

A

H2O, NH3, Cl-, Br-, CN-, OH-

37
Q

define bidentate ligand

A

able to donate 2 lone pairs of electrons to a central metal atom.

38
Q

conditions for a ligand to be multidentate

A
  • contains two or more :N or :O atoms
  • each :N or :O must be separated by at least 2 carbon atoms to allow enough stretch/bend to form two coordinate bonds at 90°
39
Q

common bidentate ligands

A 
1,2-diaminoethane (or en): H2:N-CH2-CH2-N:H2
ethanediote ion (oxalate ion): -::O(O)C-C(O)O::-
40
Q

coordination number 6 - shape

A

octahedral

90° bond angle

41
Q

coordination number 4 - shape

A

tetrahedral. 109.5° bond angle

EXCEPT complexes with platinum: square planar. 90° bond angle

42
Q

coordination number 4 - shape

A

tetrahedral. 109.5° bond angle

EXCEPT complexes with platinum: square planar. 90° bond angle

43
Q

cis-trans isomerism in a 4 bond complex ion

A

square planar (90° bond angle)
No more than 2 identical ligands eg [Pd(NH3)2Cl2]
Cis isomer - identical ligands are adjacent. 90° apart
Trans isomer - identical ligands are opposite. 180° apart

44
Q

cis-trans isomerism in a 6 bond complex ion

A

octahedral shape (90° bond angle)
monodentate: 4 of one ligand and 2 of another eg [Co(NH3)4Cl2]+
bidentate: 2 identical ligands eg [Co(en)2Cl2]+
Cis isomer - identical ligands are adjacent. 90° apart
Trans isomer - identical ligands are opposite. 180° apart.

45
Q

conditions for optical isomerism in complex ions

A

octahedral complexes only.
must contain 2 or 3 bidentate ligands.
Only cis isomers have optical isomers, trans isomers do not.
mirror images are non-superimposable

46
Q

Examples of homogeneous catalysts?

A
  • Reaction of iodide ions with S2O8(2-) catalysed by Fe2+

module 6 aromatic test (29 decks)

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