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Chem > transition metals > Flashcards

transition metals Flashcards

1
Q

What does H2O2 act as

A

Oxidising agent

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2
Q

How to oxidise transition metal complex

A

Standing in air or H2O2

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3
Q

[Fe(H2O)6]2+ with little OH- or little NH3 reaction and colours

A

Deprotonation to [Fe(H2O)4(OH)2]

Pale green solution, green ppt

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4
Q

[Cu(H2O)6]2+ with little OH- or little NH3 reaction and colours

A

Deprotonation to [Cu(H2O)4(OH)2]

Blue solution, blue ppt

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5
Q

[Fe(H2O)6]3+ with little OH- or little NH3 reaction and colours

A

Deprotonation to [Fe(H2O)3(OH)3]

Yellow solution, orange ppt

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6
Q

[Cu(H2O)6]2+ with excess NH3 and colours

A

Ligand exchange to [Cu(NH3)4(H2O)2]2+

Blue precipitate to deep blue solution

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7
Q

Conversion of chromate (VI) to dichromate (VI)

A

Acid equilibrium

2CrO42− + 2H+ ⇌ Cr2O72− + H2O

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8
Q

Chromate (VI) colour

A

Yellow

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9
Q

Dichromate (VI) colour

A

Orange

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10
Q

How far can zinc reduce dichromate (VI)

A

To Cr2+

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11
Q

How to produce dichromate (VI) from Cr3+

A

Chromium (III) to chromate (VI) using H2O2.

Addition of acid

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12
Q

Transition metal def

A

D-block elements that form one or more stable ions with incompletely-filled d-subshell.

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13
Q

Ligand

A

Molecule or ion that forms co-ordinate bond with a transition metal by donating pair of electrons.

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14
Q

Complex

A

Central metal atom or ion surrounded by ligands. Can be charged or neutral and denoted by square brackets

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15
Q

How does transition metal form coloured soln

A

Electron transitions between d-orbitals split by ligands caused by absorption of visible light. Complementary colour shown.

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16
Q

Why do some aqueous ions show no colour

A

Splitting so small/large that energy transition outside of VL range.
D subshell is full/empty therefore no electron transition possible

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17
Q

What can cause colour changes in transition metals

A 
Oxidation number (higher charge = greater splitting)
Ligand (stronger bond by ligand increases splitting)
Coordination number (change in splitting)
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18
Q

Monodentate ligand and example

A

Only can donate one pair of electrons to metal centre at a time as only one pair points to metal centre. H2O, OH-, NH3.

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19
Q

Why do complexes with 6 ligands form octahedral shape

A

Spread out to minimise electron repulsion

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20
Q

Why do some transition metal ions form tetrahedral complexes

A

Larger ligands such as chloride have such great repulsion between them that it is unstable. Due to size and negative charge.

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21
Q

Example of square planar complex

A

Cis-platin

22
Q

Why is cis-platin used and not trans-platin

A

Only cis-form is active in causing cell death

23
Q

Haem group structure

A

Multidentate ligand around Fe(II)

24
Q

Why is CO toxic

A

Oxygen molecule bound to haemoglobin replaced by CO. CO is a stronger ligand than O2 and remain bound even at low conc/

25
Q

Vanadate (V) formula and colour

A

VO2 + Yellow

26
Q

Vanadate (IV) formula and colour

A

VO 2+ Blue

27
Q

Vanadium (III) formula and colour

28
Q

Vanadium (II) formula and colour

A

V2+ Violet but oxidises back to V3+

29
Q

Chelate effect

A 
Multidentate ligands replace monodentate ligands as it introduces more disorder (higher S system)
Ligand sub is feasible if exothermic (S surr will be +ve)
if endothermic (and magnitude of S surr is less than S sys)
30
Q

Why do transition metals act as good catalyst

A

Can change oxidation state and engage in redox reactions

31
Q

Contact process (production of H2SO4) with vanadium (V) oxide

A

Overall reaction: 2SO2 + O2 -> 2SO3
1) 2SO2 + V2O5 -> 2SO3 + 2V2O4
2) 2V2O4 + O2 -> 2V2O5
Vanadium (V) oxide catalyst

32
Q

How does catalytic converter work

A

Adsorption of CO and NO molecules onto catalyst surface, weakening of chemical bonds and reaction, desorption of CO2 and N2 product molecules from surface.
2NO + 2CO -> N2 + 2CO2

33
Q

Fe2/3+ ions in reaction between I- and S2O8 2- ions

A

Both reactants negative so slow
S2O8 2- + 2Fe2+ -> 2SO4 2- + 2Fe3+
2Fe3+ + 2I- -> I2 + 2Fe2+

34
Q

Mn2+ ions in autocatalysing reaction between MnO4- and C2O4 2-
5C2O4 2- + 2MnO4 - + 16H+ -> 10CO2 + 2Mn2+ + 8H2O

A

5C2O4 2- + 2MnO4 - + 16H+ -> 10CO2 + 2Mn2+ + 8H2O
4Mn2+ + MnO4- + 8H+ -> 5Mn3+ + 4H2O
2Mn3+ + C2O4 2- -> 2CO2 + 2Mn2+

35
Q

[Co(H2O)6]2+ with little OH- or little NH3 reaction and colours

A

[Co(OH)2 (H2O)4]

Pink solution to blue precipitate (turns brown on standing)

36
Q

[Co(H2O)6]2+ with excess NH3 reaction and colours

A

[Co(OH)2 (H2O)4] to [Co(NH3)6]

Pink solution to blue precipitate that dissolves to form yellow-brown solution

37
Q

Cu2+ colour

38
Q

Co2+ colour

39
Q

Fe2+ colour

A

Pale green

40
Q

Fe3+ colour

41
Q

Cr3+ colour

42
Q

Cr2O7 2- colour

43
Q

Cr2+ colour

44
Q

CrO4 2- colour

45
Q

Reducing Cr2O7 2-

A

Using zinc and dilute acid

46
Q

Amphoteric meaning

A

Reacts with both acids and bases

47
Q

Reaction of [Cr(OH)3 (H2O)3] with base and colours

A

To [Cr(OH)6]3-

Grey-green precipitate to dark green solution

48
Q

Reaction of [Cr(OH)3 (H2O)3] with acid and colours

A

[Cr(H2O)6]3+

Grey green precipitate to green solution

49
Q

[Cu(H2O)6]2+ with Cl-

A

[CuCl4]2- Pale blue to yellow

50
Q

[Co(H2O)6]2+ with Cl-

A

[CoCl4]2- Pale pink to blue

Chem (19 decks)

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