Important Compounds of Iron- Definition, Properties, Reactions, Uses, Practice problems, FAQs.

Have you ever taken notice of your surroundings? Like the cycle you ride, the engine of the car which you travel, and the benches where you sit. Have you ever wondered what material is present in them?

It is actually iron.

Iron objects have been found in Egypt dating from around 3500 BC. Iron is the fourth most abundant element, by mass, in the Earth’s crust. The core of the Earth is thought to be largely composed of iron with nickel and sulfur. The most common iron-containing ore is haematite (Fe₂O₃), but iron is found widely distributed in other minerals such as magnetite (Fe₃O₄) and siderite (FeCO₃) . You must have seen rust on old metallic doors and windows. Have you ever thought about how this rust formed? Rust is what happens when iron comes in contact with moisture.

The first person to explain the various types of iron was René Antoine Ferchault de Réaumur who wrote a book on the subject in 1722. This explained how steel, wrought iron, and cast iron, were to be distinguished by the amount of charcoal (carbon) they contained.

Fun Fact. The Industrial Revolution which began around 18th a century relied extensively on this metal.

Let us study some important compounds related to this metal in much more detail.

Table of content:

Where is iron found?
Important compounds of iron
Ferric chloride and its properties and uses
Ferrous oxide and its properties and uses
Practice problems
Frequently asked questions

Where is iron found?

Iron is the fourth most prevalent element in the earth's crust, accounting for around 5% of its weight, and is thought to be the most important component in the planet's core. Iron is found in low amounts in the soil and is dissolved to a limited extent in groundwater and the ocean. Iron ores and minerals are numerous and widely distributed, although it is rarely encountered in nature except in meteorites.

Important compounds of iron:

There are many known compounds of iron. Some common compounds are, ferrous sulfate, ferrous nitrate,

Ferrous oxide, Ferrous phosphate, Ferric sulfate, Ferric chloride etc.
Let's study a few of them in detail.

Ferric Chloride
Ferrous oxide
Ferric oxide

Ferric Chloride (FeCl₃)

Ferric chloride is an inorganic compound consisting of an iron element with an oxidation state of +3.
Ferric chloride exists as an orange to brown-black-coloured solid and is otherwise called Molysite. The molecular formula and molecular weight of ferric chloride are FeCl3 and 162.204 g mol-1, respectively.
Ferric chloride is generally slightly soluble in water.
The solution of ferric chloride is either colourless or light brown. Ferric chloride solution has an odour of faint hydrochloric acid.
Ferric chloride solution is corrosive to human tissues and other metals as well. The non-combustible ferric chloride solution is used in the treatment of sewage and purification of water.

Synthesis of ferric chloride:

The reaction of iron and chlorine: The treatment of iron with chlorine molecules results in the formation of ferric chloride. This method is primarily used to prepare anhydrous ferric chloride.
2Fe(s)+3Cl₂(g)2FeCl₃(g)

Reaction of iron ore with HCl: Aqueous solutions of ferric chloride are obtained from iron ore as well. Iron ore produces ferric chloride solution in the presence of strong hydrochloric acid.
Fe₃O₄(s)+8HCl(aq)2FeCl₃(s)+4H₂O(aq)

Reaction of ferrous chloride with chlorine: Ferrous chloride that exists in the +2 oxidation state can produce a ferric chloride solution. The reaction of ferrous chloride and chlorine molecules produces solutions of ferric chloride having a +3 oxidation state.
2FeCl₂(s)+Cl₂(g)2FeCl₃(s)

Reaction of ferrous chloride with oxygen: Ferrous chloride, in the presence of hydrochloric acid, reacts with oxygen and yields ferric chloride solution.
4FeCl₂(s)+O₂(g)4FeCl₃(s)+2H₂O(aq)

Physical properties of ferric chloride:

The physical properties of ferric chloride are as follows:

The anhydrous form of ferric chloride has a crystalline structure with a melting point of 307.6 °C. The colour of anhydrous ferric chloride is generally orange to brown-black colour. However, it also depends on the angle from which it is viewed. Crystals that reflect light are dark green, whereas the ones that transmit light are purple-red.
Anhydrous ferric chloride consists of octahedral centres that are interconnected with the help of 2 coordinate chloride ligands. The boiling point of ferric chloride is 315 °C.
Unlike anhydrous forms of ferric chloride, aqueous solutions generally appear colourless or yellow.
Ferric chloride is highly soluble in organic solvents like diethyl ether and methanol. It is not soluble in ethyl acetate. When dissolved in water, heat is released, which means that the reaction is exothermic. The dissolution of ferric chloride in water produces an acidic solution.
Molar weight - 162.204 g mol-1 for anhydrous ferric chloride. 270.295g mol-1 for hexahydrate ferric chloride.
Color - Orange to brown-black for anhydrous forms. Aqueous solutions of iron chloride are generally colourless or yellow.
Odour - Faint HCl.
Density - Anhydrous ferric chloride - 2.90g cm^-3. Aqueous ferric chloride solution - 1.82g cm^-3
Melting point - 307.6 °C
Boiling point - 315 °C
Solubility - Highly soluble in diethyl ether and methanol. Insoluble in ethyl acetate.

Chemical reactions of ferric chloride:

Anhydrous ferric chloride is a deliquescent dark crimson solid. At around 300°C, it sublimes, and its vapour density corresponds to the dimeric formula Fe2Cl6. The dimer separates in FeCl3 which is formed at high temperatures. The dissociation into FeCl3 is a slow process. Complete at 750૦C. Above this temperature, it decomposes into ferrous chloride as well as chlorine.
Because it is soluble in non-polar solvents such as ether, alcohol, and others, anhydrous ferric chloride acts as a covalent molecule. The chlorine bridge structure represents it.
It is water-soluble. Because of its hydrolysis, the solution is acidic in nature. The reaction below shows this.
FeCl₃(s)+3H₂O(aq) ⇄ Fe(OH)₃ (s)+2HCl(aq)
To prevent hydrolysis, the solution is stabilized by adding hydrochloric acid.
Ammonia is absorbed by anhydrous ferric chloride.
FeCl₃(s)+6NH₃(g)FeCl₃.6NH3(g).
Ferric chloride is a strong oxidizer.
It converts stannous chloride to stannic chloride by oxidation.
2FeCl₃(s)+SnCl₂2FeCl₂(s)+SnCl₄(s)
It converts SO2 into H2SO4 via oxidation.
2FeCl₃(s)+ SO₂(g)+H₂O(aq)₂FeCl2(s)+H₂SO₄(aq)+2HCl(aq)

Uses of ferric chloride:

Ferric chloride finds various applications in pharmaceutical and industrial sectors as well. The various applications of ferric chloride are as follows:

Ferric chloride is used in the treatment of sewage and the purification of water.
Ferric chloride is used as a catalyst in many organic reactions. Examples include Friedel crafts alkylation and chlorination of aromatic compounds.
Ferric chloride is used in the colourimetric analysis of phenols.
Ferric chloride is additionally utilized in veterinary practice to treat animal claws overcropping, which leads to bleeding.

Ferrous oxide (FeO)

The inorganic compound FeO, also known as iron(II) oxide or ferrous oxide, is an inorganic compound with the formula FeO.
Wustite is the mineral form of it.
It is a black-coloured powder that is one of the various iron oxides.

Preparation of ferrous oxide:

The thermal breakdown of iron(II) oxalate produces FeO.
FeC2O4(s)FeO(s)+CO2(g) ↑+CO(g) ↑

To avoid the development of iron (III) oxide, this technique is carried out in an inert environment (Fe2O3)

Properties of ferrous oxide:

Below 575 °C, FeO is thermodynamically unstable and tends to decompose to metal and Fe3O4.
4FeO(s)Fe₃O₄(s)+Fe(s)
FeO is totally basic and dissolves in acids.
It has a structure similar to sodium chloride lattice, with Fe2+ ions occupying all of the octahedral holes in a cubic close-packed arrangement of O₂- ions.
Fe(OH)2 is a white solid that forms from Fe(+II) solutions, but it quickly absorbs O2 from the air and turns dark green, then brown. This is due to the fact that it first oxidises to a mixture of Fe(OH)₂and Fe(OH)₃

Uses of ferrous oxide:

It's used in cosmetics, and certain tattoo inks contain it.
It can also be used to eliminate phosphate from home aquariums.
Synthetic iron oxide has been permitted for use as a pigment in food, cosmetics, contact lenses, and pharmaceuticals.

Ferric Oxide (Fe2O3):

The inorganic compound iron(III) oxide, sometimes known as ferric oxide, has the formula Fe2O₃.

Preparation of ferric oxide:

The oxidation of iron produces iron (III) oxide. It can be made in the lab by electrolyzing an inert electrolyte solution of sodium bicarbonate with an iron anode:
4Fe(s)+3O₂(g)+2H₂O(aq)4FeO(OH)(s)

Around 200 °C, the hydrated iron (III) oxide, denoted here as FeO(OH), dehydrates and Fe2O3 is formed.

2FeO(OH)(s)Fe₂O₃ (s)+H₂O(aq)

Properties of ferric oxide:

The most important reaction is carbothermal reduction, which produces iron for steel production.
Fe₂O₃ (s)+3CO(g)₂Fe(s)+₃CO2(g)
The extremely exothermic thermite reaction with aluminium is another redox reaction.
2Al(s)+Fe₂O₃ (s)2Fe(s)+Al₂O₃(s)

Using a ceramic container to funnel molten iron in between two sections of rail, this method is used to weld thick metals such as train track rails. Weapons and small-scale cast-iron sculptures and implements are also made with thermite.

At roughly 400 °C, partial reduction with hydrogen creates magnetite, a black magnetic substance containing both Fe(III) and Fe(IV).
Fe₂O₃ (s)+H₂(g)2Fe₃O₄(s)+H₂O(s)
Ferrates (ferrate (III)) are formed by heating iron(III) oxides with other metal oxides or carbonates.
ZnO(s)+Fe₂O₃(s)Zn(FeO₂)2(s).

Uses of ferric oxide:

Iron(III) oxide is primarily used as a feedstock in the steel and iron industries, including the manufacturing of iron, steel, and a variety of alloys.
"Jeweler's rouge," "red rouge," or simply rouge is a very fine powder of ferric oxide.
The most common magnetic particle utilized in all types of magnetic storage and recording medium, such as magnetic discs (for data storage) and magnetic tape, was iron(III) oxide (used in audio and video recording as well as data storage).

Practice Problems:

Q1.With potassium ferrocyanide, ferric chloride generates a ___________ complex

a. Dark red
b. Prussian blue
c. Dark brown
d. White colour
Answer: B
With potassium ferrocyanide(Fe4[Fe(CN)6]3), ferric chloride generates a Prussian blue complex. Below is the reaction to that.

4FeCl₃(s)+3K₄Fe(CN)₆(s)Fe₄[Fe(CN)₆]₃(s)+12KCl(s)

Q2. What is the oxidation state of iron in Fe2O3?

a. +2
b. +3
c. +2
d. 0
Answer: B
Let us assume the oxidation state of Fe in Fe2O3 be x. The oxidation state of oxygen is -2 because it is in oxide form. Solving this,
2x+(-2)3=0

2x-6=0

x=+3

Hence, +3 is the oxidation state of Fe in Fe₂O₃

Q3. __________ is used to dehydrate ferric chloride.

a. Potassium ferrocyanide.
b. Stannic chloride.
c. Thionyl chloride.
d. Ammonium hydroxide

Answer: C
Thionyl chloride is used to dehydrate ferric chloride. Heat hydrated ferric chloride with thionyl chloride to dehydrate it. Below is the required reaction for that.

FeCl₃.6H₂O(s)+6SOCl₂(s)FeCl₃(s)+12HCl(aq)+SO₂(g)

Q4. The metal present in haemoglobin is

a. Mg
b. Co
c. Na
d. Fe

Answer: D
The heme group (a component of the haemoglobin protein) is a metal complex that can bind or release molecular oxygen, with iron as the core metal atom. So the correct answer comes out to be Fe.

Frequently asked questions- FAQ

Q1. What are stainless steels?
Answer: Stainless steel is formed by combining iron, carbon, and metals such as chromium, nickel, and manganese with other elements. It is rust-free.

Q2. Is it possible for humans to be poisoned by iron oxide?
Answer: When you breathe in iron oxide, it has an effect on your body. Metal vapours can create a fever when exposed to Iron Oxide emissions. This is a flu-like illness characterized by a metallic taste, fever, chills, pains, chest tightness, and cough. However, ferrous oxide (FeO) is very combustible and reactive, and it can spontaneously combust in the presence of air.

Q3. What is the purpose of black iron oxide?
Answer: Corrosion resistance is also achieved by using black iron oxide or magnetite. Black iron oxide is frequently used in anti-corrosion paints (found in many bridges, and the Eiffel Tower). Iron oxides are utilized as a contrast agent in magnetic resonance imaging to reduce proton relaxation durations.

Q4. What are the symptoms if a person is suffering from iron deficiency?
Answer: Inflammation of the corners of the mouth, an increased risk of heart illness, altered hair and nail growth, and cracked, dry, and rough skin are the most common symptoms. Iron deficiency anaemia is the most serious type.

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