Iron compounds

Introduction 

Iron has atomic number 26 and mass number 55.847.  Iron has oxidation states +2, +3.  Iron compound has electronic configuration [Ar] 4s², 3d⁶.  Iron belongs to d-block element group also called transition metal group.  Iron belongs to Group 8 and Period 4 in the periodic table.  Iron is the fourth most abundant element on earth and the most common ferromagnetic material in everyday use.  Fresh iron compound appear silvery gray.

In ancient days Iron was used but not before copper related alloys or bronze.  Pure iron is softer than aluminium but it is strengthened by adding impurities.  Iron compound is a strong metal which is widely used in construction purposes such as building houses, complex etc.  Steel is 1000 times stronger than iron.  Iron compound is smelted in blast furnace, where ore is reduced by coke to metallic iron.  Elemental iron is very reactive; it oxidizes in air to give iron oxide, also called as Rust.  Iron compounds form binary compounds with halogen and the chalcogens.

In organometallic chemistry, Ferrocene was the first sandwiched compound discovered.  Iron compounds forms complex with di oxygen as haemoglobin and myoglobin; these two compounds are very important common oxygen transport protein in vertebrate.  Iron oxide mixed with Aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ore.

Features of iron compounds

1)      Atomic radius and ionic radius of Group 8 elements: A.R. and I.R. increases down the group.

Elements	Fe	Ru	Os	Uno
A.R.  (pm)	126	134	135	-
I.R. (pm)	(+2)=77, (+3)=63	82	-	-

Where A.R.  (pm) = Atomic radius in pico meter.
              I.R.  (pm) = Ionic radius in pico meter.

2) Ionisation energy (I.E.) in Iron compound:
       1^st I.E.    =     759.3 KJ/mol.
       2^nd I.E.   =    1561.1 KJ/mol.
       3^rd I.E.    =    2957.3 KJ/mol.

3)      Non-metallic properties of Iron Compound: Iron is a metal which is a chemical element is good conductor of electricity and heat and forms cations with ionic bonds with non-metals.

4)      Melting points (M.P.) and Boiling points (B.P.) of Group 8 elements:

Elements	Fe	Ru	Os	Uno
M.P.  (0C)	1808	2810	3300	-
B.P.  (0C)	3023	4425	5300	-

5)      History of Iron compounds: Iron artifacts have been found around 3000 B.C.  A remarkable iron pillar dating about A.D.  400 is standing today in Delhi.

6)      Ores of iron compounds: Iron ores are rich in Iron oxide and vary in colour from dark grey, bright yellow, deep purple to rusty red.  The iron compound itself found in the form of

a)      Magnetite (Fe₃O₄).

b)      Hematite (Fe₂O₃).

c)      Goethite (FeO(OH))

d)     Limonite (FeO(OH).n(H₂O))

e)      Siderite (FeCO₃).

Hametite is a natural ore.  Hametite refers to early days mining.  The raw material used to make pig iron is iron ore.  The pig iron is the main raw material to make steel. 98% of mined ore is used to make steel.

Uses of Iron compounds: By adding impurities, Steel is produced.  Steel is widely used to make stainless steel plates and other various utensils.

Example of iron compounds: Iron 2 chloride

Iron 2 chloride is also called as Ferrous chloride. Its chemical formula is FeCl₂. Iron 2 chloride has high Melting point. It is a paramagnetic solid and is obtained in the form of an off-white solid. Iron 2 chloride crystallizes from water as the greenish tetrahydrate, which is used in laboratory uses and other applications. The compound is also soluble in water; aqueous solutions of Iron 2 chloride is yellow in color.
Molecular Formula of Iron 2 Chloride is FeCl₂. 4H₂O

Properties of Iron 2 chloride

Chemical properties:
 • Iron 2 chloride is Highily Corrosive substance.
• It readily causes burns.
• Inhalation of Iron 2 chloride is dangerous and touching with skin and swallowing of Iron 2 chloride is also harmful.
• Iron 2 chloride may lead to possible mutagen.

Physical properties:

• Specific gravity: 1.930g_n.
• Vapour  pressure: 10 mm @ 693 °C.

Appearance and odour:
Blue green crystals; readily oxidizes in solution

Preparation of iron 2 chloride

Wastes from steel production are made to treat with hydrochloric acid.  we get a hydrated form of Iron 2 chloride. When the hydrochloric acid is not completely consumed, such solutions are named as “spent acid,"
                             Fe + 2 HCl → FeCl₂ + H₂

Laboratory Preparation method:
Iron 2 chloride can be prepared by treating Iron powder with a solution of methanol and concentrated Hydrochloric acid under inert atmosphere. This reaction gives the methanol solvate, under vacuum heating to about 160°C gives anhydrous Iron 2 chloride.
Another laboratory method of synthesis of Iron 2 chloride is the treatment of FeCl₃ with Chlorobenzene

2 FeCl₃ + C₆H₅Cl → 2 FeCl₂ + C₆H₄Cl₂ + HCl
Preparation of Iron 2 chloride in this way shows convenient solubility in tetrahydrofuran, a commonly used solvent for the chemical reactions. In ferrocene, Wilkinson reactions generated Iron 2 chloride by heating FeCl₃ with iron powder. At high temperatures Ferric chloride decomposes to ferrous chloride.

Reactions of Iron 2 chloride

Iron 2 chloride forms complexes with many ligands. Iron 2 chloride when treated with two molar equivalents of [(C₂H₅)₄N] Cl to yield the salt [(C₂H₅)₄N] ₂[FeCl₄]. In the same way, some compounds also prepared are, [MnCl₄]²⁻, [MnBr₄]²⁻, [MnI₄]²⁻, [FeBr₄]²⁻, [CoCl₄]²⁻, [CoBr₄]²⁻, [NiCl₄]²⁻, and [CuCl₄]²⁻ salts.

Applications of Iron 2 chloride

Iron 2 chlorides is widely used in,

1. Preparation of Iron complexes.
2. In waste water treatment
3. Iron 2 chloride is used as a reducing flocculating agent in treatment with chromate containing waste water.  
4. In many of organic synthesis and reaction, Iron 2 chloride is used as a reducing agent.