1. Ionic compounds contain cations and anions that have specific chemical and physical properties. Transition metals like iron and chromium exist as cations in their ionic forms. 2. Iron can exist as the ferrous (Fe2+) or ferric (Fe3+) ion, with different electronic configurations, colors, and numbers of unpaired electrons depending on the ligand. Chromium typically exists as the Cr3+ ion. 3. Common iron and chromium compounds include salts containing the Fe2+, Fe3+, and Cr3+ ions. These compounds often have characteristic colors and are used in chemical tests and reactions that exploit the redox chemistry of iron and chromium.

1. 1

2. 2
In ionic compound
+ve charge species called cation
-ve charge species called anion
This anion or cation show specific chemical and physical property

3. 3
Electronic configuration
Fe atom Ar[3d]6 4s2 ferrous ion (Fe2+) Ar[3d]6
Cr atom Ar[3d]54S1 chromium ion ( Cr3+ )Ar[3d]4
All are d block transition metal element
Colour
Fe2+ light green
Fe3+ pale violet or brown
Cr3+ green
Unpaired electron
Ferrous ion(week field ligand or no ligand) = 4
Ferrous ion (strong field ligand) = 0
Ferric ion (week field ligand or no ligand) = 5
Ferric ion (strong field ligand) = 1
Chromium ion (week field ligand or no ligand )= 4
Chromium ion (strong field ligand) = 2
Ionic radius
Term symbol
Fe2+ ion 5D
Fe3+ ion 6S
Cr3+ ion 5D

4. 4
Ammonium iron(II)
sulfate hexahydrate
(NH4)2Fe(SO4)2 · 6H2O
Iron(II) bromide
FeBr2
Iron(II) chloride
tetrahydrate
FeCl2 · 4H2O
Iron(II) iodide
FeI2
deoxyhemoglobin
Iron(III) bromide
FeBr3
Iron(III) chloride
Iron(III) citrate
C6H5FeO7
Iron(III) oxalate
Fe2(C2O4)3 · 6H2O
oxyhemoglobin
Anhydrous
chromium(III) sulfate,
Cr2(SO4)3
Hydrated chromium(III)
sulfate
Cr2(SO4)3·18H2O
Chromium oxide
Cr2O3
chromium hydroxide
( Cr(OH)3 )

5. 5
Chlorine water readily will oxidise iron(II) (green) to iron(III)( )

6. 6
(4) Iron(II) ions reduce potassium permanganate(KMnO4)
)
(5) Fe2+ ions give octahedral cyano anionic complex ions with cyanide ions.
[Fe(H2O)6]2+
(aq) + 6CN–
(aq) ==> [Fe(CN)6]4–
(aq) + 6H2O(l)
dark blue precipitate
This is two step reaction

7. 7
(8) reaction of aqueous Fe(II) with stoichiometric amounts of NaCN under a CO atmosphere make
[Fe(CN)4(CO)2]2-
(9) Fe2+(aq) + Ce4+(aq) → Fe3+(aq) + Ce3+(aq)
(10) Iron(II) ions complex with the ethanedioate dicarboxylate anion, a bidentate ligand:
(11)Fe2+(aq) react with OH- ion of water or weak base, and loss Hydrogen

8. 8
(2)Fe3+ react with zinc, colourless zinc and pale green iron(II) ions are formed. This reaction is
usually done in the presence of dil. sulfuric acid.
(3)Fe3+ react With iodide ions, dark brown solution of iodine (or black solid) formed with iron(II)
ions.
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.
(4)Fe3+ ions give octahedral cyano anionic complex ions with cyanide ions.
This is an example of an iron complex ligand exchange reaction where six cyanide ions replace
six water molecules. This complex can be crystallised as potassium hexacyanoferrate(III)

9. 9
(5)Fe3+ ions give another anionic complex in concentrated chloride ion solutions
yellow powder
(6) Fe3+ react with K4[FeII(CN)6] dark blue precipitate
The formation of the dark blue precipitate from potassium hexacyanoferrate(II) can be used as
a test for iron(III) ion Fe3+
(aq).
(7) When in aqua solution of Fe3+ ,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.
red colour
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.

10. 10
(8) Iron(III) ions complex with another bidentate ligand, the 1,2–diaminoethane molecule (H2NCH2CH2NH2 = en )
(9)The iron(III) hexa–aqua ion is acidic. It remove H+ present of base
Fe3+ react with carbonate ion release co2 gas

11. 11
(1) Cr3+ can be reduced to Cr2+ by zinc amalgam
(2) Ammonia and salts of weak acids such as sodium carbonate ( Na2CO3 ) , ammonium sulfide ( (NH4)2S )
also precipitates Cr3+ ions as chromium hydroxide ( Cr(OH)3 ).
Addition of aqueous ammonium sulfide ( (NH4)2S(aq) ) to Cr3+
(aq) solution forms a Cr2S3 precipitate
It quickly hydrolyzes to Cr(OH)3(s) which is a green precipitate.
Cr3+ react with OH- ion
Ammonia reacts with chromium(III) ion to precipitate gray-green chromium(III) hydroxide:
This precipitate somewhat soluble in excess aqueous ammonia solution, Cr(OH)3 dissolves only to a slight
extent in excess ammonia. Boiling the solution causes the chromium(III) hydroxide to reprecipitate.

12. 12
(3) The hydroxide of Cr3+ readily dissolves in acids to form salts,
or more elaborately:
(4) Addition of NaOH, Na2O2 to Cr3+ solution forms CrO4
2-, a yellow solution
Addition of NaOH, H2O2 to Cr3+ solution forms Na2CrO4, a yellow solution
To confirm the oxidation, addition of Ba2+ solutions precipitate the yellow chromate ion, CrO4
2− as
yellow barium chromate(BaCrO4)
(5) Cr3+ can be reduced to Cr by Al

13. 13
Acidity of Cr3+
(6) [Cr(H2O)6]3+
react with base remove hydrogen
Reaction step
precipitate
This show withn OH–, NH3 and CO3
2–, & complexes

14. 14
Chromium (III) is one of the trace elements, which are necessary for human and animal vital
activity.
Chromium is important in the breakdown of fats and carbohydrates
Chromium are important for brain function and other body processes
Chromium has a functional role in glucose metabolism by increasing insulin action by its better
binding
Iron is a necessary trace element used by all known living organismsIron is an essential
constituent of hemoglobin, cytochrome, and other components of respiratory enzyme systems.
Its chief functions are in the transport of oxygen to tissue (hemoglobin) and in cellular oxidation
mechanisms.

15. 15