INORGANIC Part 10 3d block TRANSITION METALS sub–index: 10.1–10.2
Introduction 3d–block Transition Metals * 10.3
Scandium
* 10.4 Titanium * 10.5
Vanadium * 10.6 Chromium
* 10.7 Manganese * 10.8
Iron * 10.9 Cobalt
* 10.10 Nickel
* 10.11 Copper * 10.12
Zinc
* 10.13 Other Transition Metals e.g. Ag and Pt * Appendix 1.
Hydrated salts, acidity of
hexa–aqua ions * Appendix 2. Complexes
& ligands * Appendix 3. Complexes and isomerism * Appendix 4.
Electron configuration & colour theory * Appendix 5. Redox
equations, feasibility, Eø * Appendix 6.
Catalysis * Appendix 7.
Redox
equations
* Appendix 8. Stability Constants and entropy
changes *
Appendix 9. Colorimetric analysis
and complex ion formula * Appendix 10 3d block
– extended data
* Appendix 11 Some 3d–block compounds, complexes, oxidation states
& electrode potentials * Appendix 12
Hydroxide complex precipitate 'pictures',
formulae and equations
Advanced
Level Inorganic Chemistry Periodic Table Index *
Part 1
Periodic Table history
* Part 2
Electron configurations, spectroscopy,
hydrogen spectrum,
ionisation energies *
Part 3
Period 1 survey H to He *
Part 4
Period 2 survey Li to Ne * Part
5 Period 3 survey Na to Ar *
Part 6
Period 4 survey K to Kr and important trends down a
group *
Part 7
s–block Groups 1/2 Alkali Metals/Alkaline Earth Metals *
Part 8
p–block Groups 3/13 to 0/18 *
Part 9
Group 7/17 The Halogens *
Part 10
3d block elements & Transition Metal Series
*
Part 11
Group & Series data & periodicity plots * All
11 Parts have
their own sub–indexes near the top of the pages
10.8. Chemistry
of Iron Fe, Z=26, 1s22s22p63s23p63d64s2
data comparison of iron
with the other members of the 3d–block and transition metals
Z
and symbol |
21
Sc |
22
Ti |
23
V |
24
Cr |
25
Mn |
26
Fe |
27
Co |
28
Ni |
29
Cu |
30
Zn |
property\name |
scandium |
titanium |
vanadium |
chromium |
manganese |
iron |
cobalt |
nickel |
copper |
zinc |
melting
point/oC |
1541 |
1668 |
1910 |
1857 |
1246 |
1538 |
1495 |
1455 |
1083 |
420 |
density/gcm–3 |
2.99 |
4.54 |
6.11 |
7.19 |
7.33 |
7.87 |
8.90 |
8.90 |
8.92 |
7.13 |
atomic
radius/pm |
161 |
145 |
132 |
125 |
124 |
124 |
125 |
125 |
128 |
133 |
M2+
ionic radius/pm |
na |
90 |
88 |
84 |
80 |
76 |
74 |
72 |
69 |
74 |
M3+
ionic radius/pm |
81 |
76 |
74 |
69 |
66 |
64 |
63 |
62 |
na |
na |
common oxidation
states |
+3
only |
+2,3,4 |
+2,3,4,5 |
+2,3,6 |
+2,3,4,6,7 |
+2,3,6 |
+2,3 |
+2,+3 |
+1,2 |
+2
only |
outer electron config.[Ar]... |
3d14s2 |
3d24s2 |
3d34s2 |
3d54s1 |
3d54s2 |
3d64s2 |
3d74s2 |
3d84s2 |
3d104s1 |
3d104s2 |
Elect.
pot. M(s)/M2+(aq) |
na |
–1.63V |
–1.18V |
–0.90V |
–1.18V |
–0.44V |
–0.28V |
–0.26V |
+0.34V |
–0.76V |
Elect.
pot. M(s)/M3+(aq) |
–2.03V |
–1.21V |
–0.85V |
–0.74V |
–0.28V |
–0.04V |
+0.40 |
na |
na |
na |
Elect.
pot. M2+(aq)/M3+(aq) |
na |
–0.37V |
–0.26V |
–0.42V |
+1.52V |
+0.77V |
+1.87V |
na |
na |
na |
Elect.
pot. = standard electrode potential data for iron
(EØ at 298K/25oC, 101kPa/1 atm.)
na = data not applicable or not
available for iron (less common oxidation state of
iron)
Extended data table for IRON
property of iron/unit |
value for Fe |
melting
point Fe/oC |
1538 |
boiling
point Fe/oC |
2861 |
density Fe/gcm–3 |
7.87 |
1st
Ionisation Energy Fe/kJmol–1 |
759 |
2nd
IE/kJmol–1 |
1561 |
3rd
IE/kJmol–1 |
2957 |
4th
IE/kJmol–1 |
5290 |
5th
IE/kJmol–1 |
7240 |
atomic
radius Fe/pm |
124 |
Fe2+
ionic radius/pm |
76 |
Relative polarising power Fe2+ ion |
2.6 |
Fe3+
ionic radius/pm |
64 |
Relative polarising power Fe3+ ion |
4.7 |
oxidation
states Fe,
less common/stable |
+2, +3, +6 |
simple electron
configuration of Fe |
2,8,14,2 |
outer electrons of Fe |
[Ar]3d64s2 |
Electrode pot'l Fe(s)/Fe2+(aq) |
–0.44V |
Electrode pot'l Fe(s)/Fe3+(aq) |
–0.04V |
Electrode pot'l Fe2+(aq)/Fe3+(aq) |
+0.77V |
Electronegativity of Fe |
1.83 |
The
extraction of iron and steelmaking
All the details
of iron extraction from iron ores via blast furnace are given in the GCSE/IGCSE
notes on methods of extracting metals and there is little point in repeating them here
-
Starting with impure
iron from blast furnace, the molten iron contains many other
elements and the iron is too brittle initially, so there is a need to
reduce C and remove others like S and P.
-
This is achieved by
the Basic Oxygen Steel making process (BOS) which involves
many redox reactions. It is a 'batch process' and can't be
used as a continuous production line like iron from the blast
furnace.
-
Sulfur is removed
early in the process using magnesium:
-
C, P, Si and others oxidised by molecular
oxygen before scrap iron/steel introduced.
-
After the oxygen blow
the basic oxides CaO/MgO are added to form slag salts with the
weak acidic oxides of Si and P, carbon dioxide gas will
'escape' from the mixture, since any calcium carbonate formed
would thermally decompose at the high temperature of the furnace.
-
e.g. CaO + SiO2
==> CaSiO3 (calcium silicate)
-
The oxides of
Mn/Fe also collect in the slag, so some iron is wasted and the
Mn might be added in a controlled way later for a particular
steel specification.
-
The toxic carbon
monoxide formed must be dealt with and not allowed out into
the atmosphere, it can be burned as a fuel to harmless carbon
dioxide.
-
It is important to
keep track of temperature and composition by
thermocouple probe and atomic
emission spectroscopy.
-
The elements are
oxidised in a sequence in exothermic reactions (no extra heat
needed), so temperature control is essential to avoid
wasting energy and converter lining damage.
-
The added scrap
iron/steel addition acts as coolant because melting is
endothermic.
-
The whole process
must meet the specification for an individual customer requirement.
-
Dissolved oxygen
is removed with aluminium
-
and then C, Mn and Si etc. can be
re–added to a desired specification, plus any other elements,
to make a particular steel.
-
Argon (of
light bulb fame) is bubbled through to stir the mixture
because it so unreactive and most 'stirrers' will melt and
dissolve, and change the composition.
-
In the future
electric arc furnaces maybe used more to recycle steel. Big
carbon electrodes are 'sparked' to melt the scrap iron/steel, lime
added to remove impurities as slag. It is possible to use this
technology on a small scale to produce
-
Steel is an alloy
based on iron.
-
An alloy is a
mixture of a metal with at least one other element (metal or
non–metal) or compound.
-
The
composition of steel, like any other alloy, is crucial in
determining its properties.
-
Small differences
in composition can have significant effect on the properties
of an alloy.
-
Too high a % of C
in iron makes it too brittle, but a low % C makes a
stronger steel.
-
You need to
appreciate the versatile
nature of steel by changing its composition and quote some
examples.
-
There is a need
for excluding impurities eg O, P or S which lead to poor quality
material.
-
The common elements added
to iron to make steel, apart from
carbon, are usually other transition metals.
-
Scrap iron and steel is part of
BOS process and is cost effective, recycling reduces costs of (i)
ore mining extraction, (ii) possibly overseas transport and (iii)
blast furnace reduction of ore. These gains are partly offset by the
cost of collecting scrap metal.
-
In the electric
arc process only scrap steel is used and is handy technology
to produce small batches of particular steel by carefully
controlling what scrap goes in.
-
The composition of
scrap important, needs to be graded and selected to avoid problems
-
When recycling tin
cans, you need to remove the tin and other waste.
-
The cans are
shredded and paper/residual food removed, mechanical shredding
and magnetic separation can be used,
-
and de–tinning is
done by reaction with hot NaOH(aq), after which the valuable
tin can be recovered by electrolysis of the 'waste solution'.
-
A particular scrap
case study
-
There is a particular need for steel uncontaminated by radioactive
isotopes from the nuclear and atomic weapon industries.
-
For this, a useful scrap
source is from the German ships sunk at Scapa Flow has proved useful
(good geography Q and I don't remember the event!).
The
Chemistry of
IRON
Iron(II) and Iron(III) chemistry
Pd |
s block |
d blocks (3d
block
iron)
and
f
blocks of
metallic elements |
p block elements |
Gp1 |
Gp2 |
Gp3/13 |
Gp4/14 |
Gp5/15 |
Gp6/16 |
Gp7/17 |
Gp0/18 |
1 |
1H
|
2He |
2 |
3Li |
4Be |
The modern Periodic Table of Elements
ZSymbol, z = atomic or proton
number
3d
block of metallic elements: Scandium to Zinc
focus on iron |
5B |
6C |
7N |
8O |
9F |
10Ne |
3 |
11Na |
12Mg |
13Al |
14Si |
15P |
16S |
17Cl |
18Ar |
4 |
19K |
20Ca |
21Sc
[Ar]3d14s2
scandium |
22Ti
[Ar]3d24s2
titanium |
23V
[Ar] 3d34s2
vanadium |
24Cr
[Ar] 3d54s1
chromium |
25Mn
[Ar] 3d54s2
manganese |
26Fe
[Ar] 3d64s2
iron |
27Co
[Ar] 3d74s2
cobalt |
28Ni
[Ar] 3d84s2
nickel |
29Cu
[Ar] 3d104s1
copper |
30Zn
[Ar] 3d104s2
zinc |
31Ga |
32Ge |
33As |
34Se |
35Br |
36Kr |
5 |
37Rb |
38Sr |
39Y |
40Zr |
41Nb |
42Mo |
43Tc |
44Ru |
45Rh |
46Pd |
47Ag |
48Cd |
49In |
50Sn |
51Sb |
52Te |
53I |
54Xe |
6 |
55Cs |
56Ba |
57,58-71 |
72Hf |
73Ta |
74W |
75Re |
76Os |
77Ir |
78Pt |
79Au |
80Hg |
81Tl |
82Pb |
83Bi |
84Po |
85At |
86Rn |
7 |
87Fr |
88Ra |
89,90-103 |
104Rf |
105Db |
106Sg |
107Bh |
108Hs |
109Mt |
110Ds |
111Rg |
112Cn |
113Uut |
114Fl |
115Uup |
116Lv |
117Uus |
118Uuo |
|
*********** |
*********** |
************ |
************ |
************** |
********** |
********** |
********** |
********** |
********** |
|

-
The electrode potential
chart above highlights the values for various oxidation states of
iron.
-
The
most common oxidation states of iron in its compounds are +2 and +3.
-
IRON(II) and IRON(III)
Chemistry
-
Iron readily dissolves
in dilute hydrochloric or sulfuric acid to form iron(II) chloride
and
iron(II) sulfate respectively. Hydrogen gas is evolved and it is
a redox reaction.
-
The pale green
hexaaquairon(II) ion, [Fe(H2O)6]2+(aq),
is formed.
-
Fe (s)
+ 2HCl (aq) ==> FeCl2 (aq) + H2 (g)
-
Fe (s)
+ H2SO4 (aq) ==> FeSO4 (aq) +
H2 (g)
-
The redox–ionic equation
is: Fe (s) + 2H+ (aq) ==>
Fe2+ (aq) + H2 (g)
-
Hydrogen ions (H in
+1 ox. state) are reduced by electron gain to hydrogen gas (H
in 0 ox. state) and iron is oxidised from the 0 ox. state to the
+2 ox. state. Note that the lower oxidation state of iron is
formed, since neither acid is a strong oxidising agent.
-
The pale green salts FeCl2.6H2O
and FeSO4.7H2O can
be made by careful evaporation and crystallisation of the
solution.
-
However, they are readily oxidised by dissolved oxygen
to form iron(III) compounds (more on this later).
-
White anhydrous
iron(II) chloride can be made by passing hydrogen chloride gas
over heated iron.
-
If chlorine is
passed over heated iron, brown anhydrous iron(III) chloride is
formed
-

-
2Fe (s)
+ 3Cl2 (g) ==> 2FeCl3 (s)
-
An example of 'salt' synthesis by directly combining the constituent elements.
-
Iron(III) chloride is
a brown covalently bonded, relatively volatile chloride. It exists in the solid form as a
covalent molecular lattice of the dimer Fe2Cl6.
-
So, strictly speaking the
equation should be written as: 2Fe (s)
+ 3Cl2 (g) ==> Fe2Cl6(s)
-
One of the Fe's chlorines acts as a bridge, forming a dative
co–ordinate bond with the other iron atom (see diagram below).
-
-
Redox
reaction: ox. state changes are Fe (0) to (+3), Cl (0)
to (–1)
-
If the iron - halogen experiment is repeated with
bromine the reaction is less vigorous, but iron(III) bromide is still formed.
-
The exothermic nature of the reaction
may or may not be seen?
-
The dimer molecules are present in the
brown solid.
-
2Fe(s) + 3Br2(g)
==> Fe2Br6(s)
-
The reaction is easily demonstrated
by warming a little bromine with iron wool in a fume cupboard!
-
When iron wool is heated with iodine there is little
reaction, a small amount of iron(II) iodide is formed.
-
Fe(s) + I2(s) ===>
FeI2(s)
-
Fe3+ is sufficient in
oxidising power to oxidise an iodide ion to iodine, so FeI2
is formed, not FeI3.
-
This is theoretically predictable
from the half-cell electrode potentials.
-
EØI2/I–
+0.54V < EØFe2+/Fe3+ +0.77V.
-
The more positive Fe2+/Fe3+
potential will oxidise iodide to iodine.
-
If by chance any FeI3
was formed, it would decompose to FeI2 and I2.
-
The iron(III)
chloride reacts very exothermically with water to give pungent
acrid fumes of hydrogen chloride (anhydrous aluminium chloride is
made in the same way and behaves with water in the same way!).
Hence the need for dry conditions in their preparation is
illustrated below. Its also a very good idea to vent the excess
chlorine away safely!
-
FeCl3 (s)
+ 3H2O (l) ==> Fe(OH)3 (s)
+ 3HCl (g)
The sequence of ligand displacement
reactions (OH– for H2O) which occurs with any
alkali e.g. when NaOH(aq), Na2CO3(aq)
or NH3(aq) is added to a solution of an iron(II) salt or
iron(III) salt, so, the formation of iron(II) hydroxide and iron(III)
hydroxide precipitates are shown pictorially as follows ...
 |
 |
 |
The sequence of
iron(II) and iron (III) hydroxide precipitate formation. Each step is essentially one of
proton removal from each complex, from []2+ to []0
and []3+ to []0. |
 |
 |
 |
 |
-
The
oxidation of
iron(II) ions to iron(III) ions
-
i.e. the reducing action of
aqueous iron(II) ions:
-
(i) Chlorine water
readily will oxidise iron(II) to iron(III)
-
2Fe2+(aq)
+ Cl2(aq) ==> 2Fe3+(aq)
+ 2Cl–(aq)
-
Cl oxidation state change of
0 to –1
-
The pale green of the
[Fe(H2O)6]2+(aq)
ion changes to the orange colour of the
[Fe(H2O)6]3+(aq)
ion.
-
The chlorine water itself is
a very pale green, and changes to the colourless chloride ion, so the
colour change associated with the oxidation state change of iron(II) to
iron(III) is quite clearly seen.
-
Note that chlorine is a
powerful enough oxidising agent to oxidise iron(II) ion to the iron(III)
ion, BUT iodine is not a strong enough oxidising agent to achieve this.
It is in fact the iron(III) ion that will oxidise the iodide ion, rather
than the reverse.
-
The oxidising power series for
these two situations is
-
Cl2 (EØCl2/Cl–
+1.36V) > Fe3+ (EØFe3+/Fe2+ +0.77V)
> I2 (EØI2/I– +0.54V),
-
which of course is numerically
paralled by the decreasing values of the standard redox potentials of the
half–reactions i.e. becoming less positive as the oxidising power decreases.
-
So, cross–check the
reaction the
oxidation of iodide ions by iron(III) ions described below.
-
(ii) Iron(II) ions reduce
potassium manganate(VII), KMnO4
-
i.e. the manganate(VII) ion
is reduced to the manganese(II) ion
-
(i)
MnO4–(aq)
+ 8H+(aq) + 5Fe2+(aq)
==>
Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)
-
The overriding colour change
is the bright purple manganate(VII) ion being reduced to a pale colour
which is a mixture of the very pale pink manganese(II) ion and the pale
orange of the iron(III) ion.
-
more details
in manganese(VII) chemistry
-
(iii) Iron(II) ions reduce
potassium dichromate(VI), K2Cr2O7
-
i.e. the
dichromate(VI) ion is reduced to the chromium(III) ion
-
Cr2O72–(aq) + 14H+(aq) + 6Fe2+(aq)
==> 2Cr3+(aq) + 6Fe3+(aq) + 7H2O(l)
-
Theoretically, there
are actually two simultaneous colour changes.
-
The orange
dichromate(VI) ion changes on reduction to the green
chromium(III) ion,
-
and the pale green
iron(II) ion changes on oxidation to the orange iron(III) ion,
-
so I'm not sure exactly how the colour change you would
really observe would pan out!
-
more details
in chromium(VI) chemistry
-
Reactions (ii) and (iii) can be used to quantitatively estimate Fe2+
ions.
-
Oxidising action of
iron(III) ions:
-
With iodide ions,
dark brown solution of iodine (or black solid) formed with
iron(II) ions.
-
2Fe3+(aq)
+ 2I–(aq) ==> 2Fe2+(aq)
+ I2(aq/s)
-
This accounts
for why iron(III) iodide cannot exist.
-
Oxidation state
changes: iron Fe, changes from +3 to +2
-
and iodine I, changes
from –1 to 0
-
The orange–brown
iron(III) ion becomes the pale green iron(II) ion BUT the latter's
colour is obscured by the strong dark colour of the iodine formed.
-
EØ
for Fe3+/Fe2+ is +0.77V, EØ for I2/I–
is +0.54V, so Fe3+ is a stronger oxidising agent than I2.
-
Note that chlorine is a
powerful enough oxidising agent to oxidise iron(II) ion to the
iron(III) ion, BUT iodine is not a strong enough oxidising agent to
achieve this. It is in fact the iron(III) ion that will oxidise the
iodide ion, rather than the reverse.
-
The oxidising power series for
these two situations is
-
Cl2 (EØCl2/Cl–
+1.36V) > Fe3+ (EØFe3+/Fe2+ +0.77V)
> I2 (EØI2/I– +0.54V),
-
which of course is numerically
paralled by the decreasing values of the standard redox potentials of the
half–reactions i.e. becoming less positive as the oxidising power decreases.
-
So, cross–check this
reaction with the
oxidation of
iron(II) ions to iron(III) ions by chlorine described above.
-
With zinc,
colourless zinc and pale green iron(II) ions are formed. This
reaction is usually done in the presence of dil. sulfuric acid.
-
Zn(s) + 2Fe3+(aq)
==> 2Fe2+(aq) + Zn2+(aq)
-
Oxidation state
changes: Fe +3 to +2, Zn 0 to +2 (Zn2+/Zn is –0.76V, less
positive redox potential, so stronger reducing agent than Fe2+).
-
The reaction can be used
as part of a process to
titrate and analyse estimate Fe2+ and Fe3+
mixtures.
-
–
-
Simple test for
aqueous iron(III) ions:
-
Add a few drops of ammonium/potassium
thiocyanate solution (NH4SCN/KSCN).
-
A blood red
cationic complex
is formed in a ligand exchange reaction, one ligand is displaced
by another.
-
[Fe(H2O)6]3+(aq) + SCN–(aq)
==> [Fe(H2O)5SCN]2+(aq) + H2O(l)
-
This is an example of a ligand
substitution (ligand exchange) reaction.
-
Both iron(III) complex ions are
octahedral in shape with a co-ordination number of 6.
-
The oxidation state of iron
remains at +3, but the overall charge of the iron thiocyano complex
formed drops to 2+ because a + is cancelled out by the - of the
thiocyanate ion.
-
In most ligand exchange reactions
there is no change in oxidation state unless a reducing agent or
oxidising agent is present.
-
See also
Appendix 9 on
colorimetry
-
If
fluoride ions (e.g. via KF(aq)) are added the red
colour disappears immediately because a 2nd ligand displacement
reaction occurs forming the fluoro–complex ion.
-
Iron/iron(III)
oxide mixture is used as the main
component of the catalyst in the Haber Synthesis of ammonia from
nitrogen and
hydrogen.
-
Some
biochemistry of iron
-
The
biological role of iron complexes haemoglobin, myoglobin and ferritin.
-
Oxygen,
O2, molecules co–ordinate to an iron(II) ion in the
haemoglobin (hemoglobin) molecule.
-
The haemoglobin (haem)
molecule acts as a multi/polydentate ligand with iron(II) ions in
blood chemistry.
-
In an extremely
simplified form the structure is an iron(II) complex: [protein–FeII–O2].
-
('haem'
(porphyrin square
planar complex diagram to do), acts as a giant complex ion in
transportation systems of the blood i.e. the transfer of oxygen from
the lungs to all cells of the body. Transportation of oxygen is essential for respiration
- energy
release to power the biochemistry of most living organisms.
-
Unfortunately carbon monoxide forms a stronger
co-ordinate ligand bond
than oxygen and will displace it to give CO its well deserved toxic
reputation as it interferes directly with respiration processes. It only takes a small amount of CO, and a simple ligand
exchange reaction to affect the respiratory system!
-
The enzyme catalase
is extremely efficient at decomposing hydrogen peroxide
molecule in organisms. One proposed mechanism involves a
catalytic cycle of iron(III) and iron(IV) complexes e.g. if somewhat
simplified ....
-
Other complexes
of Fe2+ and Fe3+ and the cyanoferrate test for
iron(ii) and iron(III) ions
-
Iron(II) ions
complex with the ethanedioate dicarboxylate anion, a bidentate ligand:
-
Iron(III) ions
complex with another bidentate ligand, the 1,2–diaminoethane molecule
(H2NCH2CH2NH2 = en
!)
-
[Fe(H2O)6]3+(aq)
+ 3en(aq) ==>
[Fe(en)3]3+(aq)
+ 6H2O(l) colour?
-
Kstab = {[Fe(en)3]3+(aq)}
/ {[Fe(H2O)6]3+(aq)}
[en(aq)]3
-
Kstab
= 3.98 x 109 mol–3 dm9 [lg(Kstab)
= 9.6]
-
Both Fe2+ and
Fe3+ ions give octahedral cyano anionic complex ions with
cyanide ions.
-
Fe3+ ions
give another anionic complex in concentrated chloride ion solutions
-
[Fe(H2O)6]3+(aq)
+ 4Cl–(aq) ==> [FeCl4]–(aq)
+ 2H2O(l)
-
In this ligand exchange
reaction, the iron(III) complex ion shape changes from
octahedral to tetrahedral, the co-ordination number changes from
6 to 4, but the oxidation state of iron remains at +3. The
overall electrical charge on the chloro complex is -1 (from
3+/+3 and 4x-1).
-
Its likely that the more
bulky chloride ion (radius Cl > O) 'forces' the formation of the
tetrahedral shape of this iron complex ion, rather than a square planar shaped complexes.
-
Kstab = {[FeCl4]–(aq)}
/ {[Fe(H2O)6]2+(aq)} [Cl–(aq)]4
-
Kstab = 8
x 10–1 mol–4 dm12 [lg(Kstab)
= –0.097]
-
Both the hexa–aqua ions
of iron(II) and iron(III) readily complex with EDTA
-
[Fe(H2O)6]2+(aq)
+ EDTA4–(aq) ===> [Fe(EDTA)]2–(aq)
+ 6H2O(l)
-
[Fe(H2O)6]3+(aq)
+ EDTA4–(aq) ===> [Fe(EDTA)]–(aq)
+ 6H2O(l)
-
Note that the more
highly charged Fe3+(aq) ion complexes
more strongly than the Fe2+(aq) ion.
-
–
-
Summary of some
complexes–compounds & oxidation states of iron compare 3d–block
elements
-
–
RUSTING and anti–corrosion
chemistry
-
Unfortunately rust
flakes off and so it all eventually corrodes away (later
xref/contrast ZnO, Al2O3, Cr2O3
on metal surface, which do not flake away and offer good
anti–corrosion properties)
-
Factors
affecting rate of rusting
e.g. the following all speed up the
process!
-
decreasing pH,
H+(aq) ions remove OH–(aq)
formed from the reduction of O2(g/aq),
-
increased
concentration of any ions improves the conductivity of the
aqueous media, which is part of 'redox circuit',
-
and if the iron
is in contact with a 'less reactive' metal
(meaning a more +ve half–cell potential), corrosion
rates increase, because the iron is preferentially oxidised
with the more –ve half–cell potential.
-
Rust
protection–inhibition
... examples ... are x–ref with
assignment 7 on p174.
-
A plastic or
paint physical barrier to exclude water and oxygen (air),
-
Either
by (i) dipping in molten zinc, or (ii) electrolysis with Zn2+(aq)
solution and the iron/steel object as –ve cathode, galvanising
with Zn layer which results in the formation of ZnO layer.
-
The redox chemistry is similar to Fe rusting (see Fig 21) but
the layer does not flake away giving a protective layer of
zinc oxide.
-
Even if scratched, the Zn with a more
–ve
half–cell potential is preferentially oxidised.
-
Sacrificial
corrosion with blocks of Zn or Mg
and relate their
'sacrifice' to their more negative half–cell potentials, i.e.
preferentially more favourable oxidation.
-
Fe2+(aq) + 2e–
Fe(s) (EØ =
–0.44V)
-
Zn2+(aq) + 2e–
Zn(s) (EØ =
–0.76V)
-
Mg2+(aq) + 2e–
Mg(s) (EØ =
–2.38V)
-
reminder that
the reduction of oxygen to water is a positive redox potential
-
O2
(aq/g) + 2H2O(l) + 4e–
4OH–(aq)
(EØ =
+0.44V, in alkali)
-
or O2
(aq/g) + 4H+(aq) + 4e–
2H2O(l)
(EØ =
+1.23V, in acid)
-
so all the metal
oxidations are feasible BUT the most negative potential will lead to
the preferential oxidation i.e. Mg > Zn > Fe.
-
Stainless
steel via Cr addition, forms protective layer of
chromium(III) oxide.
-
History lesson in
food preservation: ‘invention’ of the tin can (tin coated
steel) ...
-
Tin plating
steel offers some corrosion protection of the iron because tin is
not a particularly reactive metal (less negative potential).
-
However, early tin cans
suffered from preferential oxidation of Fe due to its more
–ve potential, through any microscopic defect in the tin
layer, or indeed if it got scratched. This was cured by lacquer coating
as an extra protective barrier.
-
Fe2+(aq) + 2e–
Fe(s) (EØ =
–0.44V)
-
Sn2+(aq) + 2e–
Sn(s) (EØ =
–0.14V)
-
Still, fruit juice
was a problem, carboxylic acids complex with Sn2+(aq)
ions, changes Sn(s)/Sn2+(aq)
potential making it more negative than Fe(s)/Fe2+(aq),
so Sn preferentially corrodes, not toxic and contribute to
‘tangy’ taste BUT don’t keep too long as Fe eventually
will dissolve too!
-
Complex
formation affecting corrosion behaviour. Here tin(II) ions form a complex with carboxylic acids
like citric acid (tridentate ligand), by reducing the Sn2+(aq)
concentration, the Sn(s)/Sn2+(aq)
half–cell potential is then made more negative that that of iron! so
the protective thin layer of tin is sacrificially corrode, then its
the iron! Don't worry too much, the rates of reaction are slow, BUT
don't keep tinned fruit on the shelf for too long!
-
Estimation of iron
in iron(II) salts and tablet formulations.
PLEASE NOTE this page on the 3d
block transition metal iron is for Advanced A Level students ONLY!
Therefore it is IMPORTANT for GCSE/IGCSE/O Level
students studying iron chemistry to go to ...
redox chemistry of iron(II)
ions Fe2+, redox chemistry of iron(III) ions Fe3+, octahedral complexes of
iron(II) ions, octahedral complexes of iron(III) ions, polarising power of
iron ions Fe2+ and Fe3+, electrode potential of Fe2+, electrode potential of
Fe3+, oxidising reactions of the Fe3+ iron(III) ion, explain the important
biological role of iron in respiration, preparation of iron(III) chloride,
preparation of iron(III) bromide, formulae and colours and chemistry of the
hexaaquairon(II) ion [Fe(H2O)6]2+, hexaaquairon(III) ion [Fe(H2O)6]3+, tests
for iron(II) and iron(III) ions, redox chemistry of rusting of iron and how
to prevent iron rusting keywords redox reactions ligand
substitution displacement balanced equations
formula complex ions complexes ligand exchange reactions redox reactions ligands
colours oxidation states: iron ions Fe(0) Fe2+ Fe(+2) Fe(II) Fe3+ Fe(+3) Fe(III) FeCl2 FeCl3 FeSO4 Fe2(SO4)3 2Fe + 3Cl2 ==>
2FeCl3 FeCl3 + 3H2O ==> Fe(OH)3 + 3 HCl [Fe(H2O)6]3+ + H2O
[Fe(H2O)5(OH)]2+ + H3O+ 4Fe(OH)2 + O2 + 2H2O ==> 4Fe(OH)3 [Fe(OH)2(H2O)4] or
[Fe(OH)3(H2O)3] [Fe(H2O)6]2+ + 2OH– ==> [Fe(H2O)4(OH)2] + 2H2O and [Fe(H2O)6]3+
+ 3OH– ==> [Fe(H2O)3(OH)3] + 3H2O 2[Fe(H2O)6]3+ + CO32– ==> 2[Fe(H2O)5(OH)]2+ +
H2O + CO2 [Fe(OH)3(H2O)3] [Fe(H2O)6]n+ + H2O [Fe(H2O)5(OH)](n–1)+ + H3O+ MnO4–
+ 8H+ + 5Fe2+ ==> Mn2+ + 5Fe3+ + 4H2O Cr2O72– + 14H+ + 6Fe2+ ==> 2Cr3+ + 6Fe3+ +
7H2O 2Fe3+ + 2I– ==> 2Fe2+ + I2 [Fe(H2O)6]3+ + SCN– ==> [Fe(H2O)5SCN]2+ + H2O
[Fe(H2O)5SCN]2+ + F– ==> [Fe(H2O)5F]2+ + SCN– Kstab = {[Fe(H2O)5SCN]2+} /
{[Fe(H2O)6]3+} {SCN–}Kstab = {[Fe(H2O)5F]2+} / {[Fe(H2O)6]3+}
{F–}Kstab([Fe(H2O)5F]2+) > Kstab([Fe(H2O)5SCN]2+) [Fe(H2O)6]2+ + 2C2O42– ==>
[Fe(C2O4)2]2– + 6H2O Fe[Fe(C2O4)2] [Fe(H2O)6]3+ + 3en ==> [Fe(en)3]3+ + 6H2O
Kstab = {[Fe(en)3]3+} / {[Fe(H2O)6]3+} [en]3 [Fe(H2O)6]2+ + 6CN– ==> [Fe(CN)6]4–
+ 6H2O Fe2+ + [FeIII(CN)6]3– ==> Fe3+ + [FeII(CN)6]4– K+ + Fe3+ + [FeII(CN)6]4–
==> K+Fe3+[FeII(CN)6]4– [Fe(H2O)6]3+ + 6CN– ==> [Fe(CN)6]3– + 6H2O K+ + Fe3+ +
[FeII(CN)6]4– ==> K+Fe3+[FeII(CN)6]4– [Fe(H2O)6]3+ + 4Cl– ==> [FeCl4]– + 2H2O
Kstab = {[FeCl4]–} / {[Fe(H2O)6]2+} [Cl–]4 [Fe(H2O)6]2+ + EDTA4– ===>
[Fe(EDTA)]2– + 6H2O Kstab = {[Fe(EDTA)3]2–} / {[Fe(H2O)6]2+} [EDTA4–]
[Fe(H2O)6]3+ + EDTA4– ===> [Fe(EDTA)]– + 6H2O Kstab = {[Fe(EDTA)3]–} /
{[Fe(H2O)6]3+} [EDTA4–] oxidation states of iron, redox reactions of iron,
ligand substitution displacement reactions of iron, balanced equations of iron
chemistry, formula of iron complex ions, shapes colours of iron complexes
Na2CO3 NaOH NH3 transition metal chemistry of iron
for AQA AS chemistry, transition metal chemistry of iron
for Edexcel A level AS chemistry, transition metal chemistry of iron for A
level OCR AS chemistry A, transition metal chemistry of iron for OCR Salters AS chemistry B,
transition metal chemistry of iron for AQA A level chemistry,
transition metal chemistry of iron for A level Edexcel A level chemistry,
transition metal chemistry of iron for OCR A level chemistry
A, transition metal chemistry of iron for A level OCR Salters A
level chemistry B transition metal chemistry of iron for US Honours grade 11 grade 12
transition metal chemistry of iron for
pre-university chemistry courses pre-university A level revision
notes for transition metal chemistry of iron A level guide
notes on transition metal chemistry of iron for schools colleges
academies science course tutors images pictures diagrams for transition
metal chemistry of iron A level chemistry revision notes on
transition metal chemistry of iron for revising module topics notes to help on understanding of
transition metal chemistry of iron university courses in science
careers in science jobs in the industry laboratory assistant
apprenticeships technical internships USA US grade 11 grade 11 AQA A
level chemistry
notes on transition metal chemistry of iron Edexcel A level
chemistry notes on transition metal chemistry of iron for OCR A level
chemistry notes WJEC A level chemistry notes on transition metal chemistry
of iron CCEA/CEA A level chemistry notes on transition metal chemistry of
iron physical and chemical
properties of the 3d block transition metal iron, oxidation
and reduction reactions of iron ions, outer electronic
configurations of iron, principal oxidation states of iron,
shapes of iron's complexes, octahedral complexes of iron,
tetrahedral complexes of iron, square planar complexes of
iron, stability data for iron's complexes, aqueous chemistry
of iron ions, redox reactions of iron ions, physical
properties of iron, melting point of iron, boiling point of
iron, electronegativity of iron, density of iron, atomic radius
of iron, ion radius of iron, ionic radii of iron's ions, common
oxidation states of iron, standard electrode potential data
for iron, ionisation energies of iron, polarising power of
iron
ions, industrial applications of iron compounds, chemical
properties of iron compounds, why are iron complexes
coloured?, isomerism in the complexes of iron
Scandium
* Titanium * Vanadium
* Chromium
* Manganese * Iron * Cobalt
* Nickel
* Copper *
Zinc
* Silver & Platinum
Introduction 3d–block Transition Metals * Appendix
1.
Hydrated salts, acidity of
hexa–aqua ions * Appendix 2. Complexes
& ligands * Appendix 3. Complexes and isomerism * Appendix 4.
Electron configuration & colour theory * Appendix 5. Redox
equations, feasibility, Eø * Appendix 6.
Catalysis * Appendix 7.
Redox
equations
* Appendix 8. Stability Constants and entropy
changes *
Appendix 9. Colorimetric analysis
and complex ion formula * Appendix 10 3d block
– extended data
* Appendix 11 Some 3d–block compounds, complexes, oxidation states
& electrode potentials * Appendix 12
Hydroxide complex precipitate 'pictures',
formulae and equations
PLEASE NOTE this page on the 3d
block transition metal iron is for Advanced A Level students ONLY!
Therefore it is IMPORTANT for GCSE/IGCSE/O Level
students studying iron chemistry to go to ...
GCSE/IGCSE
Periodic Table Revision Notes or GCSE/IGCSE Transition Metals Revision Notes
including iron
TOP OF PAGE
|
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
Website content © Dr
Phil Brown 2000+. All copyrights reserved on revision notes, images,
quizzes, worksheets etc. Copying of website material is NOT
permitted. Exam revision summaries & references to science course specifications
are unofficial. |
|