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Chemistry > 23. Transition metals > Flashcards

23. Transition metals Flashcards

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1
Q

Define a transition metal

A

An element that forms at least one stable ion with a part full d-shell of electrons

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2
Q

Why is Scandium (21) not a transition metal

A

Only forms Sc3+ (3d0) which does not have a partially filled d orbital so is not a transition metal

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3
Q

Why is Zinc (30) not a transition metal

A

Only forms Zn2+ (3d10) which does not have a partially filled d orbital so is not a transition metal

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4
Q

Name the 4 main features which are common to transition metals

A
  • variable oxidation states
  • coloured
  • catalysts
  • complex formation
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5
Q

What does complex formation mean

A

Transition elements form complex ions

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6
Q

What is a complex ion

A

A complex ion is formed when a transition metal ion is surrounded by other ions or molecules (ligands) which are bonded by coordinate bonds

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7
Q

What is a ligand

A

An ion or molecule with a lone pair of electrons that forms a co-ordinate bond with a transition metal

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8
Q

What is the co-ordination number

A

The number of co-ordination bonds to ligands that surround the transition metal ion

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9
Q

Ions with co-ordination number six are usually…

A

Octahedral

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10
Q

Ions with co-ordination number four are usually…

A

Tetrahedral

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11
Q

Some ions with co-ordination number four are usually…

A

Square planar

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12
Q

What happens when you dissolve the salt of a transition metal ion water

A

The positively charged ion becomes surrounded by water molecules that act as ligands. These are called aqua ions.

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13
Q

What is an aqua ion

A
  • when you dissolve the salt of a transition metal ion water

- the positively charged ion becomes surrounded by water molecules that act as ligands

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14
Q

What is a multidentate ligand

A

A molecule or ion that have more than one atom with a lone pair of electrons which can bond to a transition metal ion

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15
Q

Give 3 examples of bidentate ligands

A
  • ethane- 1,2-diamine
  • ethanedioate ion
  • benzene- 1,2-diol
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16
Q

Name an important multidentate ligand that can act as a hexadentate ligand

A

EDTA 4-

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17
Q

What are chelates

A

Complex ions with polydentate ligands

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18
Q

What can chelates be used for

A

Remove d-block metal ions from solution

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19
Q

What will happen when you add a hexadentate ligand into a solution of transition metal salt

A

It will replace all six water ligands

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20
Q

Why is chelate complexes with polydentate ligands favoured over complexes with monodentate ligands

A

When polydentate ligands replace the monodentate ligands there is an increase in the number of particles and therefore entropy so it is the favourable reaction

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21
Q

What is the chelate effect

A

When chelate complexes with polydentate ligands favoured over complexes with monodentate ligands due to entropy

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22
Q

What shape is [Co(NH3)6]3+

A

Octahedral as it has 6 ligands

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23
Q

What shape is [CoCl4]2-

A

Tetrahedral as it has 4 ligands

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24
Q

What type of isomerism occurs in octahedral and square planar complexes

A

E-Z (geometrical)

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25
Q

If two Cl- ligands in an octahedral complex ion are next to each other which type of EZ isomerism is it

A

Cis or Z form

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26
Q

If two Cl- ligands in an octahedral complex ion are on opposite sides to each other which type of EZ isomerism is it

A

Trans or E form

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27
Q

When does optical isomerism occur in transition metals

A

When there are two or more bidentate ligands in a complex

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28
Q

Why are transition metal complexes coloured

A
  • because they have partially filled d-orbitals
  • it is therefore possible for electrons to move from one d orbital to another
  • in a compound d-orbitals have slightly different energies (lower = ground excited = higher)
  • when d electrons move from the ground state to the excited state they absorb light energy
  • equal to the difference in energy between levels
  • this colour is therefore missing from the spectrum
  • you see a combination of colours not absorbed
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29
Q

What does ΔE =

A

ΔE= hv
v is the frequency
h constant called Planks constant

30
Q

What effects the colour of a metal complex and why

A
  • oxidation state
  • ligands
  • coordination number
  • as the energy gap ΔE changes with each of these things
31
Q

Why do transition metals have a variety of oxidation states

A

They can use 3d and 4s electrons in bonding

32
Q

What kind of isomerism occurs with monodentate ligands

A

E-Z

33
Q

What kind of isomerism occurs with bidentate ligands

A

Optical

34
Q

Describe cisplatin

A
  • platinum transition metal
  • 2 chlorine ion ligands
  • 2 ammonia ligands
  • cis form (z form)
35
Q

What is cisplatin used for

A

Chemotherapy drug

36
Q

Give an example of a linear complex

A

[Ag(NH3)2]+

37
Q

What is [Ag(NH3)2]+

A
  • tollens reagent
  • used in organic chemistry to distinguish aldehydes from ketones
  • aldehydes reduce the [Ag(NH3)2]+ to Ag while ketones do not
38
Q

Give the equation for the difference in energy between the ground and excited state

A 
ΔE= hv
v is the frequency 
h constant called Planks constant 
or
ΔE= hc/ λ
c is velocity of light
λ is wavelength
39
Q

Name all the oxidation states of Vanadium and how they are produced

A
  • Vanadium V IV III II

- formed by the reduction of Vanadate (V) ions by zinc in an acidic solution

40
Q

When does oxidation of lower oxidation states tend to occur

A

In alkaline solutions

41
Q

Why does oxidation of lower oxidation states tend to occur in alkaline solutions

A
  • in alkaline there is a tendency to form negative ions
  • since oxidation is electron loss
  • it is easier from negatively charged species
42
Q

When does reduction of a high oxidation state occur

A

In acidic solution

43
Q

Why does reduction of higher oxidation states tend to occur in acidic solutions

A
  • in an acidic there is a tendency to form positive ions
  • since reduction is electron gain
  • it is easier from positively charged species
44
Q

How does M(H2O)4(OH)2 (typical transition metal complex) change with pH

A

acid solution: M(H2O)6 2+

alkaline solution: M(H2O)2(OH)4 2-

45
Q

How are low oxidation state transition metals such as Fe2+ stabilised against oxidation

A
  • keeping them in an acidic solution.
  • tendency to form more positive ions
  • harder to lose electrons (oxidise)
46
Q

How are transition metals with high oxidation state oxidised

A
  • alkali solution is added
  • in alkaline there is a tendency to form more negative ions
  • since oxidation is electron loss
  • it is easier from more negatively charged species
  • then oxidising agent is added
47
Q

Write the redox equation for the oxidising of Fe2+ to Fe3+ by potassium manganate (VII). During the reaction the oxidation number of manganese falls from 7+ to 2+. First construct the half equations

A

Reduction :
MnO4- (aq) + 8H+ (aq) + 5e- —-> Mn2+ (aq) +4H2O (l)
Oxidation: Fe2+ (aq) —> Fe3+ (aq) + e-
Overall:
5Fe2+ (aq) + MnO4- (aq) + 8H+ (aq) —-> 5Fe 3+ (aq)
+ Mn2+ (aq) + 4H2O (l)

48
Q

Write the redox equation for the oxidising of Fe2+ to Fe3+ by acidified dichromate (VI). During the reaction the oxidation number of chromium falls from 6+ to 3+. First construct the half equations

A

Reduction:
Cr2O7 2- (aq) + 14H+ (aq) + 6e- —> 2Cr3+ (aq) + 7H2O (l)
Oxidation: Fe2+ (aq) —> Fe3+ (aq) + e-
Overall:
6Fe2+ (aq) + Cr2O7 2- (aq) + 14H+ (aq) —>
6Fe3+ (aq) 2Cr3+ (aq) + 7H2O (l)

49
Q

Many M2+ ions will be oxidised to M3+ in what kind of solution

A

Alkaline

50
Q

Describe the process of how Co2+ can be oxidised by air to Co3+

A

By adding excess ammonia solution to solution containing Co2+ ions
1. First precipitate is formed with OH- ions from the ammonia
[Co(H2O)6]2+ + 2OH- —> Co(H2O)4(OH)2 (s) + 2H2O (l)
2.Then the precipitate dissolves in excess ammonia
Co(H2O)(OH) (s) + 6NH3 (aq) —-> [Co(NH3)6]2+ +2OH- (aq) + 4H2O (l)
3. The resulting complex ion is oxidised by air to [Co(NH3)6]3+

51
Q

How can Co2+ be oxidised to Co3+ by H2O2

A

2[Co(OH)6]4- (aq) + H2O2 (aq) —-> 2[Co(OH)6]3- (aq) + 2OH- (aq)

52
Q

What are the two groups catalysts can be divided into

A
  • heterogeneous

- homogeneous

53
Q

What are heterogeneous catalyst

A
  • catalysts that are present in a reaction in a different phase
  • usually present as solids whilst the reactants may be gases or liquid
  • reactants pass over the solid catalyst are react on its surface
54
Q

How are heterogenous catalysts made more efficient

A
  • increase their surface area
  • spread catalyst on inert support medium. Increases surface to mass ratio (used by catalytic converters)
  • do not use reactants with impurities to stop poisoning (decreases life of the catalyst)
55
Q

Why do heterogeneous catalysts not last forever

A
  • overtime the surfaces become covered with unwanted impurities (poising).
  • finely divided catalyst may gradually be lost from the support medium
56
Q

Name two processes that use heterogeneous catalysts

A
  • the Haber process

- the Contact process

57
Q

What is the Haber Process

A
  • for the production of ammonia
  • N2 (g) + 3H2 (g) 2NH3 (g)
  • iron catalyst
  • iron catalyst becomes poised by impurities in the gas stream such as sulfur
58
Q

What is the Contact Process

A
  • for the production of sulfuric acid
  • key step : 2SO2 + O2 —-> 2SO3
  • this is catalysed by vanadium (V) oxide V2O5 in two steps
59
Q

Write the two steps in which vanadium oxide catalyses the key step in the Contact process

A
  1. catalyst oxidises sulfur dioxide to sulfur trioxide and itself is reduced
    SO2 + V2O5 —> SO3 + V2O4
  2. vanadium (IV) oxide is then oxidised back to vanadium (V) oxide
    2V2O4 + O2 —-> 2V2O5
60
Q

What is a homogenous catalyst

A
  • catalysts that are present in a reaction in the same phase as the reactant
  • an intermediate species is formed
61
Q

Name an example of homogenous catalysis

A
  • Fe2+ in the

- oxidation of iodide ions to iodine by S2O8 2-

62
Q

What is the overall reaction for of the oxidation of iodide ions to iodine by S2O8 2-

A

S2O8 2- (aq) + 2I- (aq) —> 2SO4 2- (aq) + I2 (aq)

63
Q

Write the two steps in which Fe 2+ catalyses the reaction for iodide ions to iodine

A
  1. first the peroxodiosulfate ions oxidise Fe2+ to Fe3+
    S2O8 2- (aq) + 2Fe 2+ (aq) —>2SO4 2- (aq) + 2Fe3+ (aq)
  2. Fe3+ then oxidises the I- to I2 regenerating the Fe2+
    2Fe3+ (aq) + 2I- (aq) —> 2Fe2+ (aq) + I2 (aq)
64
Q

What is autocatalysis

A
  • When a product of a reaction is a catalyst for the same reaction
  • As concentration of the product builds up the speed of the reaction increases
65
Q

Name an example of autocatalysis

A

The oxidation of enthandioic acid by manganate (VII) ions ( acidificed potassium maganagte (VII) )

66
Q

Write the overall equation for the oxidation of enthandioic acid by manganate (VII) ions

A

2MnO4 - (aq) + 16H+ (aq) + 5C2O4 2- (aq) —->

2Mn2+ (aq) + 8H2O (l) + 10CO2 (g)

67
Q

How does the products of the reaction of the oxidation of enthandioic acid by manganate (VII) ions catalyse the reaction

A
  • Mn2+ ions react with the MnO4 - to form Mn3+ (the intermediate species)
  • Mn3+ then reacts with C2O4 2- to reform Mn2+
68
Q

Write the two steps where Mn2+ catalyses the reaction for the oxidation of enthandioic acid by manganate (VII) ions

A
  1. 4Mn2+ (aq) + MnO4 - (aq) + 8H+ (aq) —-> 5Mn3+ (aq) 4H2O (l)
    2.
    2Mn3+ (aq) + C2O4 2- (aq) —> 2Mn2+ (aq) + 2CO2 (g)
69
Q

Give an example of a complex ion in the body

A

Haemoglobin

70
Q

What is haemoglobin

A
  • Fe2+ ion with a coordination number of 6
  • 4 coordination sites are taken up by porphyrin (a ring system) which acts as a tetradentate ligand. This is the haem
  • 5th site taken up by nitrogen from a complex protein. This is the globin
  • 6th site can accept a oxygen molecule as a ligand
71
Q

Acidic conditions favour….

A

positive ions

72
Q

Alkaline conditions favour…

A

negative

Chemistry (27 decks)

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