Transition Metals Flashcards
(131 cards)
1
Q
what is a transition metal?
A
an element that has an incomplete d sub-shell in either its atoms or one of its common ions
2
Q
what is a ligand?
A
A ligand is a molecule or ion that forms a co-ordinate
bond with a transition metal by donating a pair of
electrons.
3
Q
what is a complex?
A
metal ion with co-ordinately bonded ligands
4
Q
what is a co-ordination number?
A
number of co-ordinate bonds from ligands to metal ion
5
Q
what is a monodentate ligand?
A
ligands which form one coordinate bond to a metal ion
6
Q
what is a bidentate ligand?
A
ligands which form 2 coordinate bonds to a metal ion
7
Q
what is a multidentate ligand?
A
ligands which form more than 2 coordinate bonds to a metal ion
8
Q
examples of monodentate ligands?
A
H2O, NH3, Cl-, OH-
9
Q
what is a Lewis base?
A
electron pair donor
10
Q
what is a Lewis acid?
A
electron pair acceptor
11
Q
what is ligand exchange?
A
reaction where one ligand in a complex ion is replaced by another
12
Q
what colour is [Cu(H2O)6]2+
A
light blue solution
13
Q
why does [Cu(H2O)6]2+ have a 2+ charge?
A
because the water ligands are not charged, so overall charge is the 2+ charge of the copper ion
14
Q
how does ammonia behave when you add a small amount to [Cu(H2O)6]2+ ?
A
as a base - accepts 2 H+ from 2 H2O ligands
15
Q
what complex is formed when a small amount of NH3 is added to [Cu(H2O)6]2+
A
[Cu(OH)2(H2O)4] (s)
16
Q
what colour is [Cu(OH)2(H2O)4] (s)
A
light blue ppt
17
Q
why is [Cu(OH)2(H2O)4] (s) solid?
A
because it is neutral, has not charge
18
Q
equation for addition of small amount of ammonia to hexaaquacopper(II) ions?
A
[Cu(H2O)6]2+ (aq) + 2NH3 —> [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
19
Q
what happens when excess ammonia is added to hexaaquacopper(II) ions?
A
ligand exchange forms [Cu(NH3)4(H2O)2]2+ (aq)
20
Q
what colour is [Cu(NH3)4(H2O)2]2+ (aq)?
A
dark blue solution
21
Q
equation for reaction of hexaaquacopper(II) ions with excess ammonia?
A
[Cu(H2O)6]2+ (aq) + 4NH3(aq) —> [Cu(NH3)4(H2O)2]2+ (aq) +4H2O(l)
22
Q
why does [Cu(NH3)4(H2O)2]2+ (aq) have a 2+ charge?
A
because neither H20 ligands nor NH3 ligands are charged
23
Q
how do you reverse the ligand exchange of hexaaquacopper(II) ions with excess ammonia?
A
flood with excess water!
24
Q
what happens when HCl is added to hexaaquacopper(II) ions?
A
ligand exchange forms [Cu(Cl)4]2-
25
what colour is [Cu(Cl)4]2-
lime green solution
26
equation for hexaaquacopper(II) ions + HCl?
[Cu(H2O)6]2+ (aq) + 4Cl- ---> [Cu(Cl)4]2- (aq) + 6H20(l)
27
why does the coordination number change to 4 when hexaaquacopper(II) ions react with HCl?
because Cl- ligands are large and charged, so repel. so only 4 join around the central Cu2+ ion
28
what colour is [Co(H2O)6]²⁺?
pink solution
29
what does NH3 act as when you add a small amount to [Co(H2O)6]²⁺ ?
a base
30
equation for [Co(H2O)6]²⁺ + small amount of NH3?
[Co(H2O)6]²⁺ (aq) + 2NH3(aq) ---> [Co(OH)2(H2O)4](s) + 2NH4+ (aq)
31
what colour is [Co(OH)2(H2O)4](s)?
green precipitate
32
why is [Co(OH)2(H2O)4](s) a ppt?
it has no charge
33
what is formed when you add an excess of ammonia to [Co(H2O)6]²⁺?
[Co(NH3)6]2+ (aq) +6H2O (l)
34
what is the difference between adding an excess of ammonia to hexaaquacopper vs hexaaquacobalt?
copper: 4 of the 6 water ligands are replaced by ammonia
cobalt: all of the ligands are exchanged
35
what colour is [Co(NH3)6]2+ (aq) ?
light brown solution
36
what is formed when HCl is added to hexaaquacobalt(ii) ?
[Co(Cl)4]2- (aq)
37
what colour is [Co(Cl)4]2- (aq)?
dark blue solution
38
why does the coordination number change when HCl is added to hexaaquacobalt?
because Cl- ligand is large and charged
39
what type of HCl needs to be added to hexaaquacobalt and copper for ligand exchange to occur?
concentrated HCl
40
is the reaction of HCl with hexaaquacobalt and copper reversible?
Yes!
41
what shape complex ions do bidentate ligands form?
octahedral (coordination no. = 6)
3 ligands bond
42
at what angle do bidentate ligands lie to each other?
right angles
43
give 2 examples of bidentate ligands?
44
what charge does ethane-1,2-diamine have?
no charge
45
show how you would draw a complex made from a cobalt ion and 3 ethane-1,2-diamine ligands?
46
show how you would draw a complex made from cobalt and 3 ethanedioate ions
47
what charge does the ethanedioate ion have?
2-
48
give 2 examples of multidentate ligands?
EDTA and haem
49
how many coordinate bonds can 1 molecule of EDTA form?
6
50
what charge does the EDTA ligand have?
4-
51
how would you write a Cu ion bonded to EDTA?
[Cu(EDTA)]2-
52
will you ever be asked to draw EDTA?
no!
53
what does haem consist of?
six coordinate bonds around a central Fe2+ ion
54
what does the shape and structure of haemoglobin allow it to do?
transport oxygen around the body
55
when deoxygenated, what is the lower ligand on haemoglobin, rather than O2?
H2O
56
why is carbon monoxide toxic to humans?
because it coordinately bonds to the haem complex in place of oxygen, meaning oxygen cant be transported around the body
57
once carbon monoxide coordinately bonds to the haem complex it is...
permanent!
58
what is the chelate effect?
Bidentate and multidentate ligands readily replace monodentate
ligands from complexes.
59
why does the chelate effect occur?
bidentate/ multidentate ligands form a more stable complex
60
what is it called when bidentate and multidentate ligands replace monodentate
ligands from complexes.
the chelate effect
61
what two key facts are needed to prove the chelate effect?
1. there is an increase in entropy when a bidentate/multidentate ligand replaces a monodentate ligand
2. enthalpy change is negligible
62
how do we know there is an increase in entropy when a bidentate/multidentate ligand replaces a monodentate ligand?
because you have more moles of products than reactants- write out the equation to demonstrate this
63
why is enthalpy change negligible when a bidentate/multidentate ligand replaces monodentate ligand?
because 6 coordinate bonds are broken and 6 are formed
64
how do you represent an increase in entropy mathematically?
positive ΔS
65
what equation links entropy change and enthalpy change?
ΔG = ΔH - TΔS
66
given than ΔH is negligible and ΔS is positive, what can we say about ΔG?
it is always negative (temp is always positive)
67
what does a negative gibbs free energy mean?
the reaction is feasible - this proves that the exchange of a mono for a bi/multi is FEASIBLE at any temperature and so will always happen READILY at any temperature
68
what type of isomerism do monodentate complexes display?
cis-trans isomerism (special type of E/Z isomerism)
69
when does cis-trans isomerism occur in octahedral monodentate complexes?
when there is a 4:2 split in the ligand type
70
when are monodentate complexes cis isomers?
when the two similar ligands are both on the same side of the complex
71
when are monodenate complexes trans isomers?
when the two similar ligands are on opposite sides of the central ion (central ion is between them diagonally)
72
what shapes of monodenate complexes display cis-trans isomerism?
octahedral (6) and square planar (4)
73
when does cis-trans isomerism occur in monodentate square planar complexes?
when there is a 2:2 split in ligand type
74
what does cisplatin look like?
when the similar ligands are next to each other
75
what does transplatin look like?
when the similar ligands are opposite each other, central ion is in the way diagonally
76
what type of isomerism do bidentate ligands show?
optical isomerism
77
how do you show optical isomerism in bidentate ligands?
dotted line down the middle, mirror images on either side (non-superimposable)
78
what are two paired optical isomers called?
enantiomers
79
key facts about optical isomers?
- non-superimposable
- will rotate plane polarised light
- it is possible to have a racemic mixture, will not rotate plane polarised light
80
what is a racemic mixture?
mixture that contains equimolar concentrations of both enantiomers. therefore will not rotate plane polarised light
81
what type of complexes does Ag+ commonly form? example?
linear complexes
e.g. [Ag(NH3)2]+ used as Tollen's reagent
82
how can transition metal ions be identified?
by their colour
83
why are transition metal complexes coloured?
due to their partially filled d orbitals
84
describe how colour arises in transition metal complexes?
1. when ligands coordinately bond, they cause d orbitals to split into 2 energy levels
2. d electrons move from the ground state to an excited
state when light is absorbed
3. ∆E is the energy difference between the ground state and excited state.
4. the frequencies of visible light that are not absorbed are reflected - this is the colour that we see
85
what does a bigger or smaller ∆E mean?
larger ∆E means higher freq of visible light is absorbed
smaller ∆E means that a lower freq of visible light is absorbed
86
what does the frequency of visible light that is absorbed by electrons determine?
the colour that we see! the colours of light that are not absorbed are reflected, and it is the combination of these that we see
87
what factors affect ∆E?
- oxidation state of the transition metal ion
- coordination number
- type of ligand
88
why are Zn2+ and SC3+ not transition metals?
if the d orbitals are full (e.g. 3d10) or empty (e.g. 3d0) then no transition or electrons can occur! therefore not transition metals
89
what is the equation for ∆E?
∆E = hf
- ∆E measured in J per atom
- h= Planck's constant (given)
- f measured in Hz
90
what equation can be used to calculate frequency?
f= c/λ
c= speed of light 3x10^8 ms^-1
λ = wavelength (m)
91
what can be used to determine the concentration of coloured ions in a solution?
colorimeter
92
transition metals show .....oxidation states
variable
93
why do transition metals show variable oxidation states?
because 4s electrons are lost before 3d when ions form. this allows them to have a number of stable electronic configurations within the partially filled d orbitals
94
how does the number of stable oxidation states change across the TMs in period 4?
number of stable oxidation states increases towards the middle of the period ie Mn has the most (7)
95
do transition metals tend to act as oxidising or reducing agents when they have a low oxidation state?
reducing agents e.g. Cr2+, Fe2+
tend to be oxidised themselves to higher oxidation states
96
do transition metals tend to act as oxidising or reducing agents when they have a high oxidation state?
oxidising agents e.g. Cr2O7 2- , MnO 4-
tend to be reduced themselves to lower oxidation states
97
what does REDOX potential mean?
tendency to lose/gain electrons
98
what 2 factors affect the redox potential of transition metals to be reduced from a higher to a lower oxidation state?
pH and ligand type
99
how does pH affect redox potential of transition metal to be reduced from higher to lower oxidation state?
transition metals more likely to be reduced in acidic conditions
100
why are transition metals more likely to be reduced in acidic conditions?
acidic conditions needed to provide H+ to complete the reaction
101
how does ligand type affect the redox potential of a transition metal?
- some ligands form stronger coordinate bonds than others
- the stronger the coordinate bond (enthalpy), the less likely the TM is to be oxidised or reduced
102
what element reduces vanadium through a number of oxidation states?
zinc
103
does zinc oxidise or reduce vanadium through a number of oxidation states ?
reduces
104
what conditions are needed for zinc to reduce vanadium through a number of oxidation states?
acidic conditions
105
what are the different colours of the oxidation states of vanadium?
106
why is zinc not able to reduce V2+ to V?
the standard reduction potential value is more positive for the Zn electrode
107
what does this symbol represent? Eo
standard reduction potential
108
what colour is MnO4-?
purple. turns colourless when reduced to Mn2+
109
what acid is used in the reaction of iron ii with permanganate?
dilute H2SO4 as SO42- ions dont interfere
110
what is the ratio of Fe2+:MnO4-?
5:1
111
what is MnO4- reduced to?
Mn2+
112
what is C2O4 2-oxidised to?
2CO2
113
what is the ratio of C2O4 2- to MnO4- ?
1: 2.5
114
what is a heterogeneous catalyst?
a catalyst that exists in a different phase to the reactants.
usually a solid TM in an aq or g reaction
115
what are two examples of heterogeneous catalysts?
Fe(s) in the Haber Process
V2O5(s) in the Contact Process
116
equation for the Haber process catalysed by Fe
117
what are the 2 reactions in the Contact Process?
118
what ways can the efficiency of a reaction be increased, to do with a solid catalyst?
- increase surface area e.g. grind up the catalyst
- spread solid catalyst over a support medium e.g. honeycomb framework
119
what causes efficiency of heterogeneous catalysts to decrease over time?
poisoning - impurities stick to the surface of catalyst (block active site) and block interaction between catalyst and reactants
120
what are homogeneous catalysts?
catalysts that exist in the same phase at the reactants
121
when catalysts and reactants are in the same phase, how does a reaction proceed?
through an intermediate species
122
why does the following reaction have a high Ea before a catalyst is added?
because the negative ions repel
123
what species will catalyse the following reaction?
Fe^2+ (aq)
124
what is the definition of autocatalysis?
when one of the products of a reaction acts as a catalyst for that reaction
125
in the reaction between in the reaction
between ethanedioic acid and
acidified potassium manganate(VII), what product is the catalyst for that reaction?
Mn^2+
126
equation for the reaction
between ethanedioic acid and
acidified potassium manganate(VII)?
127
explain the graph for an autocatalysis reaction, with conc of MnO4- on the y-axis and reaction on the x-axis
- slow start due to a low concentration of Mn2+ (catalyst)
- as conc of Mn2+ increases, the rate increases
- reaction slows down towards end as the conc of MnO4- nears 0
128
what is the fact that transition metals can serve as catalysts owed to?
the fact that transition metals have variable oxidation states
129
explain how catalysts work?
1. reactants ADSORB onto the surface/ active site of the catalyst
2. reaction takes place/ bonds weaken
3. products DESORB/ leave the surface of the catalyst
130
what is the term for when reactants attach tot the surface of a catalyst
adsorb
131
what is the term for when products leave the surface of a catalyst?
desorb
