Transition metals Flashcards
(56 cards)
1
Q
what is a transition element
A
- element that forms at least one stable ion with an incomplete D sublevel
2
Q
what is a ligand
A
- a molecule or ion that forms a co-ordinate bond with a transition metal atom or ion
3
Q
what is a complex
A
- a central metal atom or ion surrounded by ligands joined by coordinate bonds
4
Q
what is the coordination number
A
- the number of coordinate bonds to the central metal atom or ion
5
Q
what complexes have a linear shape and describe their features
A
- Ag⁺ complexes only
- bond angle = 180
- coordination number of 2
6
Q
what complexes have a square planar shape and describe their features
A
- only platinum (Pt²⁺) and nickel(Ni²⁺)
- bond angle = 90
- coordination number of 4
7
Q
what complexes have a tetrahedral shape and describe their features
A
- when ligands are too big to fit 6 (Cl⁻)
- bond angle = 109.5
- coordination number of 4
8
Q
what complexes have an octahedral shape and describe their features
A
- most complexes
- bond angle = 90
- coordination number of 6
9
Q
what is a monodentate ligand
A
- a ligand that forms one coordinate bond to the transition metal ion
10
Q
why do complexes containing Cl ligands form a different structure than those containing H₂O ligands
A
- Cl ligands are bigger than other ligands and therefore can only fit 4 Cl ligands
11
Q
what type of isomerism occurs in monodentate metal complexes + explain
A
- Cis-Trans Isomerism
- Cis = ligands are 90 degrees away
- Trans = ligands are 180 degrees away
12
Q
what shape of metal complexes does Cis-Trans isomerism occur in?
A
- octahedral
- square planar
13
Q
what is a bidentate ligand
A
- ligand which forms two co-ordinate bonds to a metal ion via two different atoms on the same ligand
14
Q
what are the two bidentate ligands
A
- 1,2 diaminoethane (H₂NCH₂CH₂NH₂)
- ethanedioate ions (C₂O₄)²⁻
15
Q
what type of isomerism occurs in metal complexes containing at least 2 bidentate ligands
A
- optical isomerism
16
Q
what is a multidentate ligand
A
- a ligand that can form 2 or more coordinate bonds to a transition metal ion
17
Q
what multidentate ligand do we need to know
A
- (EDTA)⁴⁻
18
Q
why does EDTA most effective in alkaline conditions
A
- the OH⁻ reacts with the H⁺ causing equilibrium to shift to the right ensuring the EDTA can form 6 coordinate bonds
19
Q
what are the uses of EDTA
A
- used to treat patients with lead poisoning by making the toxic ions present in the body harmless (chelation therapy)
20
Q
what is Haemoglobin and what does it contain
A
- its an iron complex that transport oxygen around the body
- it contains the central iron ion and a multidentate ligand called a porphyrin ring which forms 4 coordinate bonds (haem unit)
21
Q
describe the structure of haemoglobin in oxygen rich conditions
A
- each haem unit is bonded to a protein called globin via a lone pair on the nitrogen of the globin
- 4 coordinate bond from the porphyrin ring to the Fe leaving one more space for oxygen to bind and act as a monodentate ligand via coordinate bonding
22
Q
why does carbon monoxide prevent the transport of oxygen
A
- when carbon monoxide is inhaled it forms a coordinate bond with the Fe²⁺ ion in the haem unit blocking the O₂ from binding
23
Q
where do Cl⁻ ligands come from
A
- Concentrated HCl
24
Q
what is the chelate effect
A
- ligand substitution reaction between multidentate ligand and monodentate ligand complexes to form more stable multidentate ligand complexes due to an increase in entropy
25
why does the chelate effect work
- increase in entropy as more moles of products are produced than moles of reactants therefore product is more stable
26
why would the ΔG value for a ligand substitution reaction between ligands that form the same type of coordinate bond always be negative
- increase in entropy as more moles of products are produced than moles of reactants therefore product is more stable
- enthalpy change will be 0 as the same bonds that are broken are made again
- since ΔG = ΔH - TΔS , ΔS is positive, ΔH=0, ΔG will be negative
27
describe how to reduce Vanadium (V) to Vanadium (II)
- dissolve NH₄VO₃ in sodium hydroxide solution to ensure VO₂⁺ is the main ion present
- transfer to a small conical flask and add small amount of zinc powder + HCl
- put cotton wool in the neck of the flask and swirl the flask
28
why is cotton wool put in the neck of the conical flask when reducing vanadium ions
- to allow H₂ gas to escape but also minimise the oxidation of the vanadium ions
29
what are the colours of the vanadium ions in their variable oxidation states
- V⁵⁺ (VO₂⁺) - yellow
- V⁴⁺ (VO²⁺) - blue
- V³⁺ (V[H₂O]₆)³⁺- green
- V²⁺ (V[H₂O]₆)²⁺- violet
30
how are vanadium ions reoxidised
- let them stand in air due to the O₂
- add concentrated nitric acid
31
what causes colour changes of transition metals (3)
- change in oxidation state
- change in coordination number
- change in ligand/type of ligand
32
why are transition metals coloured
- d orbitals to split in energy level
- certain wavelengths of light are absorbed by sample causing electrons to be promoted from ground state to excited state
- wavelengths of light that aren't absorbed are transmitted giving off a certain colour
33
equations to calculate energy gap when given frequency of light absorbed
- ΔE = hv
- energy gap = Planck's constant x frequency of light absorbed
34
equations to calculate energy gap when not given frequency of light absorbed
ΔE = hc/λ
- energy gap = (Planck's constant x speed of light)/wavelength of light absorbed
35
how would you determine the concentration of a transition metal ion
- add an appropriate ligand to intensify the colour
- set the colorimeter wavelength to λmax
- make up standard solutions of known concentrations of the metal ion, some higher and some lower
- measure absorbance of standard solutions and plot a graph of absorbance value against known concentrations (calibration graph)
- measure the absorbance of the unknown solution and determine its concentration from the graph
36
how to intensify the colour of a pale complex
- add a suitable ligand to intensify the colour
37
what are Heterogeneous catalysts
- catalysts that are in a different phase to the reactants
- usually a solid and the reaction takes place on the surface
38
what are some important heterogeneous catalytic processes
- the Haber process - industrial production of Ammonia
- the Contact process - production of sulfuric acid
39
how do heterogeneous catalysts work
- reactants are adsorbed onto active sites on catalysts surface
- reaction occurs with lower activation energy as bonds are weakened or new bonds are made between reactants that are being held close together
- the products are desorbed
40
how is the efficiency of a heterogeneous catalyst maximised
- by using a thin coating of the catalyst on a support medium in order to maximise surface area to save costs
41
what are the equations and catalyst involved in the production of Ammonia
- catalyst = Fe (s)
- N₂ (g)+ 3H₂ (g) ⇌ 2NH₃ (g)
42
what are the equations and catalysts involved in the contact process
- catalyst = V₂O₅ (s)
- overall eq = 2SO₂ (g) +O₂ (g) → 2SO₃
- actual eq = SO₂ + V₂O₅ → V₂O₄ + SO₃
½O₂ + V₂O₄ → V₂O₅
43
how can heterogeneous catalysts be poisoned
- impurities adsorb to the surface blocking the active site lowering its efficiency or making it totally ineffective
44
examples of poisoned heterogeneous catalysts
- lead poisoning of catalytic converters in cars
- the hydrogen in the Haber process is contaminated with sulfur leading to sulfur poisoning
45
what are homogenous catalysts
- catalysts that are in the same phase as the reactants
- usually in the aqueous state
46
what are some important homogeneous catalytic processes
- reaction between iodide ions (I⁻) and persulfate ions (S₂O₈²⁻) with Fe²⁺/Fe³⁺ as a catalyst
47
why does the reaction between iodide ions (I⁻) and persulfate ions (S₂O₈²⁻) have a high activation energy
- both reactants are negatively charged and therefore repel each other
- high energy is needed to overcome that repulsion
48
why does the reaction between iodide ions (I⁻) and persulfate ions (S₂O₈²⁻) occur faster with Fe²⁺/Fe³⁺ ions
- opposite charges on the ions attract , therefore lower the activation energy making the reaction faster
49
what is the overall equation involved in the reaction between iodide ions (I⁻) and persulfate ions (S₂O₈²⁻) with Fe²⁺/Fe³⁺ as a catalyst
overall : S₂O₈²⁻ + 2I⁻ → 2SO₄²⁻ + I₂
50
what are the actual equations involved in the reaction between iodide ions (I⁻) and persulfate ions (S₂O₈²⁻) with Fe²⁺/Fe³⁺ as a catalyst
actual :
- S₂O₈²⁻ + 2Fe²⁺ → 2SO₄²⁻ + 2Fe³⁺
- 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂
51
what is autocatalysis
- when one of the products from a reaction is a catalyst for the reaction
52
what is an example of autocatalysis
- the reaction between ethanedioate ions (C₂O₄²⁻) and manganate ions (MnO₄⁻) with Mn²⁺ catalyst
53
what is the source of ethanedioate ions
- ethanedioic acid
54
what is the overall equation involved in the reaction between ethanedioate ions (C₂O₄²⁻) and manganate ions (MnO₄⁻)
5C₂O₄²⁻ + 2MnO₄⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ +8H₂O
55
what are the actual equations involved in the reaction between ethanedioate ions (C₂O₄²⁻) and manganate ions (MnO₄⁻)
step 1: 8H⁺ + MnO₄⁻ + 4Mn²⁺ → 5Mn³⁺ + 4H₂O
step 2: 2Mn³⁺ + C₂O₄²⁻ → 2CO₂ + 2Mn²⁺
56
why does the rate of autocatalysed reactions change over time
- reaction is slow at first until some of the catalyst is formed
- after a substantial amount of catalyst is formed the rate of reaction increases until the reactant runs out
