Transition Metals Flashcards
1
Q
Describe the properties of d-block metals
A
- malleable, ductile
- low reactivity
- hard dense
- Tm is high
2
Q
Define a transition element
A
Forms at least one stable ion with an incomplete d shell
3
Q
Why are Sc and Zn are not transition metals
A
Sc only forms Sc3+: No e- in d sub shell
Zn only forms Zn2+ : Completely full sub shell
4
Q
Describe the following properties that make transition metals unique
A
- variable oxidation state
- form coloured compounds
- form complex ions
- used as catalysts
5
Q
What are coordinate bonds
A
- one atoms supplies both electrons required for the covalent bond
6
Q
What is a ligand?
A
- an ion or molecule with a lone pair of electrons that forms a coordinate bond with a transition metal
7
Q
What is a monodentate ligand?
A
- forms one coordinate bond with a transition metals ion
:CN- :NH3 :OH- :Li-
8
Q
What are bidentate ligands?
A
- forms two coordinate bonds with a transition metals ion
- ethanedioate
- 1,2-diaminoethane
- benzene-1,1-diol
9
Q
What is a multidentate ligand?
A
- forms multiple coordinate bonds with a transition metals ion
EDTA
10
Q
Wray is a complex?
A
- a transition metals ion surrounded by ligands bonded by coordinate bonds
11
Q
What is a coordination number?
A
- the number of coordinate bonds to ligands which surround the transition metals ion surrounded ion
12
Q
What are aquaions
A
- hydrated transition metals ions
13
Q
What is a Lewis’s acid
A
- electron pair acceptor
14
Q
What is a Lewis base
A
- electron pair donor
15
Q
What is a haem
A
- a complex of iron (II) surrounded by a porphyrin ring (multidentate ligand)
- 4 nitrogen atoms in the ring form 4 coordinate bonds to the iron (II) ion
16
Q
What is haemoglobin
A
A protein structure containing 4 haem groups bonded to 4 globular proteins called a and b units
17
Q
Describe isomerism within square planar complex ions
A
- cis/trans isomerism
18
Q
Describe isomerism within octahedral complex ions
A
- monodentate ligands: cis/trans
- bidentate ligands: voptical
19
Q
Why are transition metals ion surrounded complexes coloured
A
- when there are no ligands, d orbitals are degenerate
- when there are ligands, they push d orbitals to higher energy levels
- gap between ground and excited state corresponds to energy in the visible region of the spectrum
20
Q
Describe why Cu2+ ions are blue
A
- Ions absorb light
- D electrons are excited
- The colour of light observed is the light that is not absorbed
21
Q
What is the equation that inks energy difference between the ground state and the excited state with the frequency and wavelength of light absorbed
A
ΔE = hν
ΔE = hc/ λ
(ν = c/ λ)
22
Q
What does the magnitude of ΔE depend on?
A
- Type of transition metals ion surrounded ion
- The oxidation state of the transition metal ion
- Type and number of ligands
- Shape of the complex
23
Q
What transition metal complex appears blue
A
[Cu(H2O)6]2+
- Octahedral
24
Q
A
25
What transition metal complex appears yellow/green?
[CuCl4]2-
- tetrahedral
26
What is 1nm in m?
1x10-9
27
Why is Zn2+ colourless?
- d orbitals are full
- no d block electrons can be excited
- no light absorbed
28
What is a ligand substitution reaction??
- when a ligand in a complex is replaced by another ligand
- often causes a change in colour
29
Explain why the ΔH of some ligand substitution reactions are 0
- same number of bonds formed
- same type of bonds broken and formed
30
Is there a change in enthalpy when there is a change in coordination number
Yes
31
Is an exothermic or endothermic ligand substitution reaction more favourable
- exothermic
32
Is a positive or negative entropy change more favourable in a ligand substitution reaction?
Positive (chelate effect)
33
What is the chelate effect
- chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands
34
How does absorbance relate to concentration
Proportional
35
How do you measure the concentration of an unknown solution?
Produce a calibration curve
1. Select appropriate filter colour
2. Make up samples of different concentrations
3. Place them in colorimeter and record absorbances
4. Plot calibration graph
5. Measure the absorbance of your unknown solution and convert absorbance into concentration
36
How do you work out the formula of a complex ion using colorimeters?
- colour of a complex changes when ligand substitution happens
- absorbency of solutions containing different ratios of metal ion and ligand are measured
37
Describe method 1 of working out the formula of a complex ion using calorimeter
1. Keep moles of complex ion the same and gradually increase ligand until rate of change of absorbance changes
2. When maximum substitution has occurred and the most stable complex has formed, colour stops changing as rapidly
38
Describe method 2 of working out the formula of a complex ion using colorimeters
1. Start with zero moles of complex and excess ligand
2. Increase moles of complex and decrease moles of ligand
3. Once maximum substitution has occurred the most stable complex is formed, absorbance will decrease
39
Why do transition metals have variable oxidation states?
- both the 4s and 3d electrons can be used in bonding
40
What does the oxidation state of the metal dictate?
- colour
- chemical properties of the metal
41
Why do all transition metals form a metal with an oxidation state of 2 (M2+)
- 4s2 electrons can be removed
42
Describe the trend in stability of the 2+ oxidation state across the period
Increase
- increasing nuclear charge so remaining electrons become more tightly held
43
Describe the scenario in which high oxidation states exist
- transition metal ion is covalently bonded to electronegative elements
- MnO4-
- Cr2O72-
- VO2+
44
What are the factors that determine how easy it is to change the oxidation state of a transition metal?
1. Effect of ligand
2. Effect of pH
45
Are transition metals in higher oxidation states oxidising or reducing agents?
- oxidising
46
are transition metals in lower oxidation states oxidising or reducing agents?
- reducing agents
47
What are vanadium’s 4 most common oxidation states?
+5, +4, +3, +2
Yellow, blue, green, violet
48
What is the formula for vanadium with a +5 oxidation state
VO2 +
49
What is the formula for vanadium with a +4 oxidation state
VO 2+
50
What is the formula for vanadium with a +3 oxidation state
V3+
51
What is the formula for vanadium with a +2 oxidation state
V2+
52
What are redox titrations used for?
- quantitative volumetric analysis
53
How can the end point of redox titrations be determined
1. Electrically
2. Colour change (self indicating, MnO4- -> Mn2+, purple to colourless)
3. Indicator
54
What is the half equation for the reduction of MnO4-?
5e- + 8H+ + MnO4- -> Mn2+ + 4H2O
55
What condition is required when doing a redox titrations?
- sample being oxidised must be acidified
- acid must not be oxidised by metal (use electrode values)
- acid must not reduce oxidising agent
56
What is a heterogenous catalyst?
- in a different phase or state to the reactants
57
Describe how heterogeneous catalysts work to provide an alternate pathway
1. Reactants are ADSORBED onto active sites on the surface of the catalyst
2. Reactants are held in favourable orientation
3. Bonds in the reactants are weakened, making the reaction easier
4. Product molecules are described from the surface
58
What happens if a catalyst becomes poisoned by impurities in the reaction mixture?
- catalyst becomes inactive
- active sites on surface become blocked
59
What is the catalyst within the haber process?
N2 + 3H2 <-> 2NH3
Iron
- pea sized lumps to increase surface area
- poisoned by sulphur compounds/impurties
60
What is the contact process
- production of sulphuric acid
- conversion of SO2 -> So3 using vanadium oxide catalyst
V2O5 + SO2 -> V2O4 + SO3
V2O4 + 1/2O2 -> V2O5
SO2 + 1/2O2 -> SO3
61
What is a homogenous catalysts
- Catalyst in the same phase as the reactants and an intermediate species is formed
Catalysed route:
- Reactant 1 + catalyst -> intermediate
- intermediate + reactant 2 -> catalyst + products
62
What is an example of a reaction using a homogenous catalyst
S2O8 2- + 2I- -> 2SO42- + I2
- requires a catalyst as these are both negative ions
- therefore there is repulsion leading to a slow reaction
Catalysed by: Fe2+ or Fe3+
63
Give the equations for the catalysis of S2O8 2- and I- ions
2Fe2+ + S2O82- -> 2Fe3+ + 2SO42-
2Fe3+ + 2I- -> 2Fe2+ + I2
64
What is autocatalysis
- product of a reaction is a catalyst for the reaction
- reaction starts slowly until concentration of the catalysis product builds up enough
- then behaves as a normal reaction
E.g 4Mn2+ + MnO4- + 8H+ -> 5Mn3+ + 4H2O
2Mn3+ + C2O42- -> 2Mn2+ + 5CO2
Mn2+ is the catalyst
