Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

A-Level Chemistry > Inorganic Unit 2.5: Transition Metals > Flashcards

Inorganic Unit 2.5: Transition Metals Flashcards

1
Q

define transition metal

A

an element that has an incomplete d sub-shell in either its atoms or its common ions
Ti-Cu

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the properties of transition metals?

A

formation of complexes
formation of coloured ions/compounds
variable oxidation states
catalytic activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define ligand

A

a molecule or ion that forms a co-ordinate bond with a transition metal by donating a lone pair of e-s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define complex

A

central metal atom/ion surrounded by ligands co-ordinately bonded

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define co-ordination number

A

the number of co-ordinate bonds from ligands to the central metal atom/ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

define Lewis base

A

lone pair donor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

define Lewis acid

A

lone pair acceptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe the formation of complexes

A

ligands form co-ordinate bonds with transition metal ion by donating their lone pair of e-s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe the formation of complexes in terms of Lewis acid & Lewis base

A

ligands act as Lewis bases when they bond to transition metals as they donate a lone pair of e-s to form a co-ordinate bond
the transition metal ion acts as a Lewis acid as it accepts this lone pair of e-s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are examples of common ligands?

A

H2O (small)
NH3 (small)
Cl- (big)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

table of common shapes of complexes

A

co-ordination number
shape
occurrence
example
see booklet

tetrahedral with large ligands (Cl-)
octahedral with small ligands (H2O & NH3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the different types of ligands & define them

A

unidentate/monodentate - ligands which form 1 co-or. bond to a metal ion
bidentate - ligands which form 2 co-ord. bonds to a metal ion (form cycles)
multidentate - ligands which form more than 2 co-of. bonds to a metal ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

list unidentate ligands

A

:Cl-
:OH-
:CN-
H2O:
:NH3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

give 2 bidentate ligands

A

1,2-diaminoethane (en) H2NCH2CH2NH2
ethanedioate ion (C2O4^2-) the O binds to the TM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what makes a cycle (formed from bidentate ligands) less stable?

A

the further the bond angle is from 109.5, the less stable the cycle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

give 2 multidentate ligands

A

EDTA4- forms 6 bonds
porphyrin forms 4 bonds e.g. in haemoglobin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

describe the structure of haemoglobin & how does oxygen bind?

A

haem is an iron(II) complex with a multidentate ligand
haemoglobin has 4 haem groups (each with a porphyrin ligand taking up 4/6 co-ord. sites)

O2 forms a co-ord. bond to Fe2+ in haemoglobin, enabling oxygen to be transported in the blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

why are CO & CN- toxic?

A

it replaces oxygen by forming a co-ord. bond to Fe2+ in haemoglobin
CO & CN- are better ligands than O2 as they form stronger co-ordinate bonds with Fe2+
so bond to haemoglobin in preference to oxygen
so they prevent O2 transport around the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

when does each type of stereoisomersim occur in complexes?

A

cis-trans isomerism can be displayed in:
octahedral complexes with monodentate ligands
square planar complexes
when there are 2 of the same ligands that are different to the other ligands

optical isomerism can be displayed in:
octahedral complexes with at least 2 bidentate ligands (often 3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

draw a pair of isomers for each type of isomerism

A

see booklet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what linear complex is used in Tollen’s reagent?

A

Ag+ forms [Ag(NH3)2 ]+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

define ligand substitution/exchange

A

reaction where one ligand is replaced by another ligand

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what happens in substitution of similar sized ligands & give example equations with Co2+ & Cu2+

A

H2O & NH3 are similar in size
no change in co-ordination number
see booklet for equations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what happens in ligand substitution reactions that are incomplete?

A

only some of the ligands are replaced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what happens in substitution of larger or smaller ligands & give example equations with Co2+, Cu2+, Fe3+
co-ordination number can change e.g. Cl- ligands are larger than NH3 & H2O only 4 Cl- ions can bond to most transition metals so co-ordination number goes from 6 to 4
26
what is the chelate effect?
substitution of ligands that form more co-ordinate bonds bidentate & multidentate ligands replace monodentate ligands the resulting complex ions are more stable
27
describe the chelate effect in terms of ΔH, ΔS & ΔG
ΔH is negligible bc same type & number of co-ordinate bonds are being broken & formed when ligands are replaced by those that form more co-ord. bonds, there is a large increase in entropy (Δ S) because more molecules are formed than reacted ΔG is -ve so ligand substitution where ligands are replaced by those that form more co-ord. bonds are feasible
28
what are chelating agents?
ligands that form more than one co-ordinate bond (often form many) they bond easily to metal ion & are v difficult to remove —> so metal ion cannot bond to anything else so is harmless
29
what ligand is a good chelating agent & why?
EDTA4- as it forms 6 co-ordinate bonds
30
why are complexes coloured?
presence of ligands around central metal ion causes split in energy b/w d orbitals e-s absorb UV/visible light so e-s are promoted from lower energy orbital to higher energy orbital the observed colour is the frequency of light transmitted/reflected
31
when does colour arise?
when some wavelengths of light are absorbed & the remaining wavelengths are transmitted or reflected
32
what happens to e-s when light is absorbed?
d e-s move from the ground state to an excited state
33
what is the formula for the energy difference b/w ground state & excited state of the d -s
ΔE = hv = hc/λ ΔE - energy gap h - Planck's constant v - frequency of light c - velocity of light λ - wavelength of light
34
what factors affect the colour of a complex?
identity of metal oxidation state of metal identity of ligands co-ordination number --> which influences the shape of the compound
35
what metal ions are not coloured & why?
Zn2+ as d sub-shell is full Cu+ as d sub-shell is empty Sc3+ d sub-shell is empty so e-s cannot be promoted from the lower to higher energy d orbitals
36
how is the concentration of coloured ions in a solution determined?
colorimetry
37
how is the absorption of visible light using in spectroscopy?
frequencies at which a complex absorbs UV/visible light can be measured w a UV/visible light spectrometer UV/visible light is passed through the complex & frequencies passing through/transmitted are detected frequencies that do not pass through are absorbed the more concentrated the solution, the more light is absorbed & the less light is transmitted
38
how does colorimetry work?
the more concentrated a solution, the more it absorbs for some ions, a ligand is added to intensify the colour a colour of light is chosen that the compound absorbs the strength of absorption of a range of solutions with known concentrations is measured & calibration curve produced the conc. of a solution with unknown conc. is found by measuring the absorption & reading off the calibration curve
39
what are common oxidation states of iron, manganese & copper?
Fe: +2, +3, +6 Mn: +2, +4, +6, +7 Cu: +1, +2
40
what are the uses of variable oxidation states?
testing for aldehydes: Tollen's reagent - [Ag(NH3 )2]+ is reduced Fehling's solution - Cu2+ reduced to Cu+ testing for alcohols: acidified potassium dichromate K2Cr2O7 Cr2O72- --> Cr3+ Cr (+6) is reduced to Cr (+3) redox titrations: acidified KMnO4 used to analyse Fe2+, C2O4- & H2O2 catalysis: reactions catalysed by TM often involves TM changing oxidation state
41
what does 'redox potential' mean?
how easily it is to change the oxidation state of a TM
42
what does redox potential for a TM depend on?
pH & the ligand
43
how does pH affect redox potential of TM?
in general it is easier to: oxidise a TM in alkaline conditions = oxidising agent in alkaline conditions promotes the higher oxidation state reduce a TM in acidic conditions = reducing agent in acidic conditions promotes the lower oxidation state
44
how are the effect of ligand, effect of pH & effect of ligand & pH shown with electrode potentials?
see booklet less -ve emf for reduction shows complex is easier to reduce
45
how is vanadium in ammonium vanadate(V) reduced?
reduced from V(+5) to V(+4) to V(+3) to V(+2) in acidic conditions (HCl or H2SO4) using zinc as the reducing agent cotton wool inserted into neck of flask to keep air out to prevent reoxidation
46
what are the species present & the colour for each oxidation state of vanadium?
V(+5) - VO2 + - yellow V(+4) - VO 2+ - blue V(+3) - V 3+ - green V(+2) - V 2+ - purple
47
in what conditions prevents V(+5) from being reduced to V(+2)?
alkaline conditions
48
redox titration calculations
see booklet & practice
49
what are the conditions for using potassium manganate as an oxidising agent & why can't specific acids be used?
dilute H2SO4 is used (as S cannot be oxidised bc it is +6) HCl cannot be used as MnO4- would also oxidise Cl- to Cl2 toxic gas which increases the volume of KMnO4 required in the titration conc. H2SO4 & conc. HNO3 cannot be used as they are oxidising agents so decrease the volume of KMnO4 required in the reactions ethanoic acid cannot be used as it is a weak acid so does not provide enough H+ ions
50
describe the use of acidified KMnO4 in redox titrations
purple KMnO4/potassium manganate (VII) is in the burette & sample being analysed is in the flask with XS dilute H2SO4 as KMnO4 is added it reacts to form colourless Mn2+ at the end point, the excess purple MnO4- does not react so end point is pink titration is self-indicating
51
what is the half equation for reduction of MnO4-?
MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O
52
dilute H2SO4 can be used with any oxidising agent to create acidic conditions
53
describe the analysis of Fe2+ in redox titrations & give half equation & overall equation
analysed in redox titrations with acidified KMnO4 half equation: Fe2+ --> Fe3+ + e- overall equation: 5Fe2+ + MnO4- + 8H+ --> 5Fe3+ + Mn2+ + 4H2O reacting ratio of Fe2+ to MnO4- is 5:1
54
what happens if iron is not in +2 oxidation state?
if as element Fe (0), it reacts with H2SO4 --> Fe2+ ready to analyse if is it Fe3+ then it is reacted with zinc to reduce it to Fe2+ ready for analysis
55
describe the analysis of ethanedioate/C2O4- in redox titrations & give half equation & overall equation
analysed in redox titrations with acidified KMnO4 half equation: C2O42- --> 2CO2 + 2e- overall equation: 5C2O42- + 2MnO4- + 16H+ --> 10CO2 + 2Mn2+ + 8H2O the reacting ratio of C2O42- to MnO4- is 2.5:1 or 5:2
56
why is the reaction of C2O42- & MnO4- slow?
C2O42- & MnO4- are both negative so they repel each other so reaction needs warming at the start of the titration so takes some time for purple manganate (VII)
57
how does Mn2+ act as a catalyst (give equations)?
4Mn2+ + MnO4- + 8H+ --> 5Mn3+ + 4H2O +ve & -ve attract so fast 2Mn3+ + C2O42- --> 2CO2 + 2Mn2+ +ve & -ve attract so fast
58
define autocatalysis
a reaction where one of the products is a catalyst
59
what is a catalyst & how do they work?
substance that increases the rate of a chemical reaction but is not used up in the reaction catalysts provide an alternative route of lower activation energy catalysts do not change ΔG, ΔH or ΔS
60
define heterogeneous catalyst
a catalyst that is in a different phase to the reactants usually a solid & the reaction takes place at active sites on the surface of the catalyst in Q, define heterogeneous & then define catalyst
61
how do heterogeneous catalysts work?
at least one of the reactants is adsorbed onto the active site on the surface of the catalyst molecules can move about the surface, bonding to different active sites
62
define adsorb
form bonds to the atoms in the solid surface
63
how does the adsorption of reactants onto the surface of a catalyst increase the rate of reaction?
it concentrates the reactants i.e. brings them closer together than in gas phase it can weaken some of the bonds in the molecule, making the reaction easier it can position the molecule in favourable orientation --> so increases # successful collisions per second
64
give 2 examples of industrial processes that involve heterogeneous catalysts
Haber process: Fe catalyst 2H2 + N2 <--> 2NH3 Contact process V2O5 catalyst 2SO2 + O2 <-->2SO3
65
what happens when adsorption is too weak?
not many molecules will be adsorbed so the catalyst has little effect
66
what happens when adsorption is too strong?
molecules cannot move around active sites so are less likely to collide with particles of another reactant so less likely to react product often stays adsorbed to the surface of the catalyst
67
graph of adsorption strength vs rate of transition metals
see booklet
68
what is the effect of the catalyst having a large surface area?
less quantity of catalyst needed to produce the same effect/to increase the rate of reaction by the same amount
69
how is surface area of a catalyst maximised?
using a v thin coating of catalyst on a support medium honeycomb structure often used this minimises the cost
70
describe catalyst poisoning
other substances/impurities adsorb strongly to the surface of the catalyst, which blocks the active sites this reduces the efficiency of the catalyst the poisons are difficult to remove so catalyst is ruined, which can be costly
71
examples of catalyst poisoning
lead poisoning of catalytic converters in cars Rh & Pt poisoned by lead sulphur poisoning in the Haber process hydrogen is obtained from natural gas, which can be contaminated with S S poisons Fe catalyst
72
describe the Contact process
manufacturing H2SO4 SO2 --> SO3 is a slow, reversible reaction catalysed by vanadium(V) oxide V2O5: V2O5 + SO2 --> V2O4 + SO3 V2O4 + 1/2O2 --> V2O5 overall: SO2 + 1/2O2 --> SO3
73
define homogeneous catalyst
a catalyst that is in the same phase as the reactants often happen in solution
74
what happens when catalysts & reactants are in the same phase?
the reaction proceeds through an intermediate species, which reacts further to form the product faster than the original reactant & to regenerate the catalyst
75
how does an acid homogeneous catalyst work?
e.g. esterification 1. the acid protonates one of the reactants: X + H+ --> HX+ 2. the species produced (HX+) then reacts with the other reactant, giving the products & reforming the catalyst (HX+ reacts faster than X): HX+ + Y --> products + H+
76
how does a transition metal homogeneous catalyst work?
TM compounds can vary oxidation states, which allows them to act as catalysts
77
describe the reaction of I- + S2O82- & give the equations
2I- + S2O82- --> I2 + 2SO42- reaction is slow in absence of catalyst bc 2 -ve ions repel so collision is difficult catalysed by Fe2+(aq) or Fe3+(aq) bc it can easily change b/w the oxidation states 1. 2Fe2+ + S2O82- --> 2Fe3+ + 2SO42- Fe2+ reduces S2O82- to SO42- Fe2+ is oxidised to Fe3+ 2. 2Fe3+ + 2I- --> 2Fe2+ + I2 Fe3+ oxidises I- to I2, reforming Fe2+ NB these reactions can happen either way round
78
describe autocatalysis by Mn2+ in the reaction b/w MnO4- & C2O42-
2MnO4- + 16H+ + 5C2O42- --> 2Mn2+ + 8H2O + 10CO2 slow without catalyst bc -ve ions repel catalysed by Mn2+(aq) which can act as a catalyst bc it easily changes b/w oxidation states Mn(+2) & Mn(+3) the catalyst is a product of the reaction - the reaction is slow until some Mn2+ is formed, then it speeds up
79
define autocatalysis reactions
reactions which produce their own catalyst
80
what is the equation for the catalysed reaction of Mn2+ reducing MnO4- to Mn3+?
4Mn2+ + MnO4- + 8H+ --> 5Mn3+ + 4H2O
81
what is the equation for Mn3+ oxidising C2O42- to CO2, reforming Mn2+?
2Mn3+ + C2O42- -->2CO2 + 2Mn2+
82
draw & label the graph of rate vs time
does not start at 0 rate increases as [Mn2+ catalyst] increases rate then decreases as [reactants] decreases see booklet

A-Level Chemistry (22 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions