Category: Chemistry Notes PPT

Phosphorus hailing from the family of nitrogen is a non-metallic chemical. This chemical is pale, transparent, semi-transparent, odourless, and tasteless in nature. It is not available freely in nature in any form. Being the 15th element in the periodic table, phosphorus emits flumes when put in contact with air. It is stored in water in most chemical laboratories to avoid catching fumes or fire. 

The occurrence of phosphorus in the crust of the earth is about 0.12% and occurs as phosphate. The United States, the largest producer of phosphorus, mined 13,300,000 metric tons in the year 1996. Bone ash and urine were the first primary sources of phosphorus. 

Discovery of Phosphorus

The discovery of phosphorus dates back to 1669 by Hennig Brand. Strongly believing that urine had the capacity to transform lead into gold paved the way to the discovery of this non-metallic chemical. Further, he started heating and purifying about 60 buckets of urine just to find out the magical element that could turn into gold. It was exactly then he discovered ‘Phosphorus’. 

Properties

There are three allotropic forms of phosphorus – they are pale or white phosphorus, red and black phosphorus.  The phosphorus chemical element properties and reactions vary as per these forms.

• Red Phosphorus – Red phosphorus is commonly seen on one side of the matchstick. The red phosphorus is formed as a result of heating white phosphorus at 250 degrees celsius. It does not dissolve in liquids. 

• Black Phosphorous – The black one is obtained by heating white phosphorus in really high pressure. 

• Black Phosphorous – The black one is obtained by heating white phosphorus in really high pressure. It resembles graphite. 

Phosphorus is classified into group 15 of the periodic table. It is solid as per the physical state. 

Medical Uses of Phosphorus

Phosphorus-32 is the radioactive isotope. Its uses are varied. It is used in various medical treatments such as the polycythaemia vera. It helps detect tumours in various parts of the body, such as the brain, breasts, etc. The radiations of radioactive isotope phosphorus-32 treat cancer. 

Reactions

The shell arrangement of phosphorus is like the arrangement of nitrogen. The 3 half orbits form a single covalent bond. When combined with various elements, phosphorus shows oxidation. Phosphorus is said to have larger atoms and low electronegativity which influences its properties and reactions. Unlike nitrogen, phosphorus allows the expansion of octet, which leads to the formation of 5 covalent bonds in compounds. 

Biological Aspects of Phosphorous

Phosphorus is found as phosphate in the body. Phosphate is found in the DNA and RNA of the human body. Phosphorus is an active part of the distribution of energy throughout the human body. 

The recommended dietary intake of phosphate is 800 mg per day. Some of the foods that are rich in phosphorus are turkey, chicken, tuna, eggs, salmon, cheese etc. Consumption of phosphate in larger quantities than that which is required leads to serious health issues like osteoporosis, kidney problems etc. Exposure to white phosphorus sometimes leads to drowsiness, nausea, stomach pain etc., in some people. 

Applications of Phosphorus in Industrial Use

Phosphorus is utilized in the production of steel, in the manufacture of fertilisers, improving the quality of the crop or soil. It can yield phosphine and phosphorus oxyacids which are used in commercial pest control. They are used as smoke screens, incendiary fire or bombs in the field of the military. Other industrial uses of phosphorus are – 

1. Flame retardant

2. Aid in processing 

3. Metal alloy constituent 

4. Intermediates 

5. agricultural chemicals 

6. Material recovery

7. Plastic production 

8. Fabricated metal product manufacturing 

9. Resin manufacture 

10. Organic chemical manufacture etc. 

Variable Oxidation State 

The variable oxidation state of phosphorus goes from -3 to +5. 

Sample Questions and Answers

1. What are the Properties and Uses of Red Phosphorus? 

Ans: Red phosphorus is derived by heating the white phosphorus. It is stable when compared to white phosphorus. Its melting point is at 860K. 

There are many uses of red phosphorus – used in matchsticks, production of pesticides, organic synthesis, production of smoke bombs, water softening, electroluminescent coating, etc. 

2. Who Discovered Red Phosphorus? 

Ans: Red phosphorus was discovered by an Australian chemist named Anton von Schrotter. He discovered it in the process of heating white phosphorus at 482 degrees celsius in the presence of nitrogen. 

3. Is Phosphorus Present in the Human Body? 

Ans: Yes, phosphorus is present in the human body. It is found in the liver, kidney tissues, brain, blood, saliva, urine. 

Those reactions which are not of 1st order but approximated or appear to be of 1st order due to higher concentration of the reactant/s than other reactants are known as pseudo-first-order reactions. The order of a chemical reaction can be defined as the sum of the power of concentration of reactants in the rate law expression is called the order of that chemical reaction. Reactions can be a first-order reaction, second-order reaction, pseudo-first-order reaction, etc. depending on the concentration of the reactants.

Explanation of Pseudo First-order Reaction 

With the help of the dependency of the rate of reactions on the concentration of reactants, we can determine the order of the reaction. If the order of the reaction is zero, the rate does not depend on the concentrations of reactants. In the same way, if the order of the reaction is one, the rate of reaction is proportional to the first power of the reactant concentration. We will discuss pseudo-first-order reactions in detail. 

Suppose a reaction is – aA + bB  cC + dD 

Rate according to rate law expression = k[A]x[B]y

Where x and y are concentrations of A and B respectively. 

So, order of reaction will be = x + y

We can say x is the order of reaction with respect to A and y is the order of reaction with respect to B. 

Now if suppose x=1 and y = 1 then the reaction will be a 2nd order reaction. But if the concentration of B is much more than the concentration of A then the change in concentration of B will be very less so its concentration can be assumed constant. So, in this condition, although the reaction is of 2nd order in nature but can be approximated as 1st order reaction with respect to A and known as pseudo 1st order reaction. 

The graph of Pseudo first-order reaction is given below.

()

Thus, the pseudo-first-order reaction is actually of a higher-order reaction but can be approximated or appears to be the pseudo-first-order reaction. We can say in general pseudo order reactions are those reactions that appear to be of xth order reaction but can be approximated or are of some different order. 

Pseudo First Order Reaction Example 

Pseudo-first-order reaction can be well explained by the following examples – 

1. Hydration of Alkyl halide 

CH3I + H2O CH3OH + H+ + I–

Rate of reaction = k [CH3I] [ H2O]

As methyl iodide is also used in aqueous solution form so the concentration of water is far higher than methyl iodide. 

 [CH3I] <<< [ H2O]

So, the concentration of water doesn’t change much and can be approximated as no change or constant. 

Now we can write – Rate of reaction = k’ [CH3I]

Where k’ = k [H2O]

Thus, the reaction appears to be first-order, but it is actually of second-order that’s why it is known as a pseudo-first-order reaction. 

 2. Hydrolysis of Cane Sugar 

C12H22O11 + H2O  C6H12O6 + C6H12O6

Sucrose      Water      Glucose      Fructose 

Rate of reaction = k [C12H22O11] [H2O]

But [H2O] >>> [C12H22O11]

So, the concentration of water can be approximated as constant as its concentration doesn’t change a lot during the reaction. 

Now the rate of reaction can be written as – 

r = k’ [C12H22O11]

where k’ = k [H2O]

thus, hydrolysis of cane sugar is a pseudo-first-order reaction. 

3. Hydrolysis of ester 

Reaction – CH3COOC2H5 + H2O         CH3COOH      +     C2H5OH 

              Ethyl ethanoate  Water          Ethanoic acid        Ethanol 

Rate of reaction = k [CH3COOC2H5] [H2O]

But [H2O] >>> [CH3COOC2H5]

So, we can say the concentration of water remains almost constant during the reaction. 

So, we can write –

Rate of reaction = k’ [CH3COOC2H5]

K’ = k [H2O]

Thus, hydrolysis of the ester is a pseudo-first-order reaction.

Conclusion

In this article, we learned about the pseudo-first-order reaction. With the help of different examples of pseudo-first-order reactions, we get to know different reactions that are not of first-order reaction but appear to be of 1st order due to higher concentration of the reactants.

All radicals in chemistry are also referred to as free radicals because the radical in chemistry is an atom that consists of at least one unpaired valence electron with them. These unpaired electrons make the radicals highly reactive elements with few exceptions. Most of these radicals have a short life span, and they tend to easily dimerize instantly with other atoms of the same kind. One of the most notable examples of radicals is the hydroxyl radical, which has one unpaired electron situated on an oxygen atom. The two other major examples of radicals in chemistry are triple oxygen and triplet carbene (꞉CH₂), which have two unpaired electrons.

The radicals may generate in a number of ways but the most prominent and easy methods for the formation of the free radicals are ionisation radiation, redox reaction heat, electrical discharges, and electrolysis which results in the production of free radicals. Radicals form an intermediate product in many of the chemical reactions that are very much evident from the balanced equations. In chemistry like combustion, atmospheric chemistry, polymerisation, plasma chemistry, biochemistry, and many other chemical processes, radicals play an important role. 

The radical generating enzymes are the prime element for the production of many of the naturally occurring products. The radicals such as nitric oxide and superoxide and their products in living organisms play a very crucial role in regulating many important processes such as controlling vascular tone and thus blood pressure. They are also known to regulate many intermediary metabolisms of various biological compounds. For a process dubbed redox signalling, such radicals can even be a messenger. It can be bound or trapped in a solvent cage. 

()

Properties of Free Radical

All the structure of the free radicals has a common property that they have at least one unpaired electron present in their atomic orbital and still can exist independently. Generally, the molecules possess the bonding pair or the lone pair of electrons that are unbonded, also referred to as unshared pair of electrons. The electrons present in each bonding and the non-bonding pairs have opposite spin orientation, +1/2 and -1/2 in the orbital depending on Paul’s Exclusion Principle. But an unpaired electron in the radical is just one single electron that is present in the orbital. Thus, the atom or ion containing the single electron is known as a free radical and is a paramagnetic species. Therefore, some of their properties are as follows:

1. They are rare and unique species that are present in very special conditions that are very limited in nature. However, we are certain of some of the free radicals in our daily lives. 

2. Molecular oxygen is a biradical molecule that is one kind of free radical. The stable molecule of oxygen is in a triple molecular state where the two unpaired electrons present in each oxygen atom have the same spin orientation in different orbitals. They also have the same orbital energy based on Hund’s rule. 

3. Nitrogen monoxide and nitrogen dioxide are the two species that are considered stable free radical species. Moreover, oxygen radical is the reactive species that are involved in immunity that consists of singlet molecular oxygen and superoxide anion radical. 

4. Free radicals thus are very familiar to us and are an important part of our immunology, and support major biological activities.

5. Free radicals are very unstable and thus are highly reactive in nature. They are the unique species that has the ability to both donate the electrons or accept the electrons and, therefore, acts as reactants or oxidants. 

Examples of Radicals

The examples of free radicals are methyl radicals. Three reactive species are considered, which are methyl anion and methyl cation along with methyl radical. These free radicals have been illustrated below.

()

Ethane is composed of two methyl groups that are highly stable in nature and are connected to each other through covalent bonds. The methyl cation and the methyl anion have a positive charge and lone pair of electrons that make the methyl and negatively charged where the carbon is connected to the counter iron with an ionic bond. It is a rather moisture-sensitive species but not particularly unstable in nature.

But the methyl radical is extremely unstable in nature and therefore is very reactive. It is because the octane of carbon is not completely filled. The carbon in the methyl cation is obtained for SP² hybridization which gives it a structure that is triangular and planar. The carbon atom in the methyl anion comprises SP³ hybridisation, which gives it a tetrahedral structure. But the carbon atom in the methyl radical adopts a middle structure that lies between methyl cation and methyl anion. Therefore, we get a structure that is a pyramid and the rapid inversion occurs at extremely low temperatures. Some of the other examples of such free radicals contain Oxygen and hydroxyl radicals.

• Hypochlorite

• Hydrogen peroxide

• Nitric oxide radical

• Superoxide anion radical

• Peroxynitrite radical

Types of Free Radicals

Most of the organic radicals are unstable in nature and therefore become highly reactive. Therefore, there are two types of free radicals, namely e neutral radicals and charged radicals, as shown below.

()

There are also two kinds of different radicals known as Sigma radicals and the pi radicals. The unpaired electron in the Sigma radical is in the Sigma orbital, whereas the unpaired electron in the pi radical is in the PI orbital, respectively. Therefore, the radicals that are illustrated are the PI radicals where le t-butyl radical is also considered as Pi radical as it is stabilised by the hyperconjugation, where the Sigma radicals have phenyl radicals and vinyl radicals as examples. 

Generally, the resonance effect on the hyperconjugation effect stabilises the PI radicals but since there is no such stabilising effect for the Sigma radicals, therefore, they are very reactive in nature.

Uses and Source of Free Radicals

The sources of free radicals that are generated internally are as follows:-

• Inflammation

• Mitochondria

• Phagocytosis

• Exercise

• Peroxisomes

Externally the free radicals are found in the following sources.

• Ozone layer

• Drugs and pesticides

• Radiation

• Environmental pollution

• Smoking cigarette

Following are the uses of free radicals, as mentioned below.

1. The membrane of the cell that is damaging biologically relevant molecules such as DNA lipids, proteins, carbohydrates etc., contains the highly reactive structures of free radicals.

2. Mini micro molecules that lead to cell damage and homeostatic disruption, such as proteins and nucleic acids, has been attacked by the free radicals.

3. The radical
   precursors for R or Ar generally use up the alkyl halides or aryl halides, but what are the sugars and the nucleus eyes have many age groups and other delicate functional groups; therefore, the halogenation of these groups is rather difficult.

4. For the radical reactions in sugars nucleosides in peptides, the Barton Mccombie reaction is very useful.

5. Along with phenoxy thiocarbonate chloride, the other thiocarbonyl derivatives that are formed from alcohol can be put to use in place of methyl xanthate.

Some of the major radicals are given in the form of radical chat, which is as follows:

Radical Chat in Chemistry

Reactivity series is the series of metals based on their reactivity from highest to lowest. So, the reactivity series of metals can be defined as a series of metals, in order of reactivity from highest to lowest. It is also known as activity series. The reactivity of metals is because of their incomplete outer orbitals or due to their electronic configuration. Metals form positively charged ions as they tend to lose electrons. Metals with high atomic numbers tend to be more reactive as their electrons are far from the positively charged nucleus, so, they can be removed easily. 

 

()

 

Long Tabular Form of the Reactivity Series 

 

Metals from potassium to calcium are highly reactive and even react with water. While metals from magnesium to lead can react with acids. Metals from copper to platinum are highly unreactive and don’t react with any other substance in normal conditions. This is the reason why platinum and gold don’t get corrode easily and don’t form oxides. While metals such as zinc, aluminium, magnesium, calcium, etc. form oxides readily. Hydrogen is a non-metal but still, it has been included in the reactivity series as it helps in the comparison of reactivity of metals.

 

The reactivity of the metals is given below in another tabular format where it has been mentioned along with its ions. Here metals are segregated in terms of their reaction with cold water, hot water, acid, and steam and reaction with concentrated mineral acids. Here is the tabular format of the same.

 

 

Salient Features of reactivity seri
es

• Metals present at the top of the reactivity series are highly electropositive metals. The electropositive character of metals decreases as we go down the series. 

• The reducing power of metals decreases as we go down the series. Thus, potassium is the strongest reducing agent. 

• As we go down the reactivity series, the ability of metals to remove hydrogen from hydrides decreases. 

• Metals present in the reactivity series above hydrogen can remove hydrogen ions from dilute HCl or Dilute sulphuric acid. 

• The metal which is more reactive than other metals can remove less reactive metal from its salt. Thus, metals placed at the top of the reactivity series can remove the metals which are present at the bottom of the series from their salts. 

• The metals which are placed above in the series can be extracted by electrolysis. While metals from Zinc to Hg can be extracted by simply reducing their oxides, which is an inexpensive method.  

• When we move down the series the electron-donating capacity of metals decreases.

Important Uses of Reactivity Series 

• In displacement reaction – Displacement reactions are those reactions in which more reactive metal displaces less reactive metal from its salt. So, by reactivity series, you can tell which metal will displace another metal. 

• The reaction between metals and water – Metals from potassium to calcium can react with cold water and release hydrogen gas. 

Chemical Equations for the reaction of K and Ca with cold water are:

Reaction 1:   

K (s) + H₂O (l) → KOH (aq) + ½ H₂ (g)

 

Potassium Cold Water Potassium Hydroxide Hydrogen

 

Note: Potassium reacts extremely violently with water to form a colourless aqueous solution of KOH with a release of12mole of H2 gas. The resultant solution is basic because of the dissolved hydroxide.

Reaction 2:

Ca + H₂O (l) → Ca(OH)₂ (aq) + ½ H₂ (g)

Calcium Cold Water Calcium Hydroxide Hydrogen 

 

Note: Ca virtually remains unreactive with cold water; however, it forms calcium hydroxide with a release of half a mole of H₂ gas.

• The reaction between metals and acids – Lead and other metals which are more reactive than lead in the reactivity series can react with hydrochloric acid and sulphuric acid and form salts. Thus, we can predict the reactions by reactivity series. Chemical Equations for the reaction of Pb with HCl and HSO₄ to form salts are: 

Reaction 1:   

 Pb (s) + 2HCl (aq) → PbCl₂ (aq) + H₂ (g)

Lead Hydrochloric Acid Lead Chloride Hydrogen

 

Note: Pb reacts slowly with acids like HCl and HNO₃ and releases bubbles of Hydrogen gas on reaction.

 

Reaction 2:   

Pb (s) + 2 H₂SO₄ → PbSO₄ + SO₂ + H₂O

 

Lead Sulphuric acid lead Sulphate (II) Sulphur Dioxide Water  

 

Note: Lead does not react with sulphuric acid, that’s why the reaction takes place in the boiling solution. Lead on reacting with 2 moles of HSO4, forms lead sulphate (II), sulphur dioxide with the release of water.

 

Single displacement reaction between metals: The high-ranking metals on the reactivity series readily reduce the ions of the low-ranking metals. Thus the high-ranking metal easily displaces the low-ranking metal in a single displacement reaction that occurs between them. One of the most common displacement reactions is the displacement of copper from copper sulphate by zinc the chemical equation for this reaction is given by:

 

Zn (s) + CuSO_{4 (}aq) → ZnSO₄(aq) + Cu (s)

 

This concept is used in various applications mostly for the extraction of metals. For example, with the help of the single displacement reaction with magnesium titanium can be extracted from titanium tetrachloride. Thus to predict the outcome of the single displacement reaction, the reactivity series becomes very useful.

 

Short Trick to Remember Reactivity Series

“Please send charlie’s monkeys and zebras in lead & hydrogen cages in mountains securely guarded by Plato.” 

In the above-given sentence, first alphabet of every word denotes the elements of the reactivity series in order of their reactivity from highest to lowest. You can understand this better by the table given below.

Resin is a material that is extracted from the secretions of plants and trees. In this article, we are going to understand Resin, its types, properties, uses, and more. Students will get to know about Resin and its concepts. The industry experts have designed it in an easy to understand manner. So, without any further ado, let us understand what Resin is in the coming section.

What is Resin?

Secondary metabolites are organic compounds that are produced by bacteria, fungi, and plants. These molecules do not control growth, development, and reproduction directly. They are generally called specialized molecules. These molecules mainly exist as toxins, secondary products or natural products. Resin is a type of secondary metabolite. In this article, we have covered all the important points like Resin definition, the structure of Resin, and its composition. 

 

Let’s come to the main question, what is Resin? Resins are solid or semi-solid amorphous products of complex chemical nature containing many carbon atoms. The word “Resin” is also used to refer to the high-viscosity liquid or semi-solid produced by the polymerization of Resin acids. Resin is created in various forms. It can appear in a solid, powdery, or liquid form. The most common Resin types are copal, dammar, mastic, and shellac.

 

Definition of Resin

Resin: “any of various solid or semisolid amorphous fusible flammable natural organic substances that are usually transparent or translucent and yellowish to brown are formed especially in plant secretions are soluble in organic solvents (such as ether) but not in the water, are electrical nonconductors, and are used chiefly in varnishes, printing inks, plastics, and sizes and medicine.”

()

Types of Resin

Resin can be divided into two types, depending on the nature of synthesis. Resin is of two types:

1. Natural Resin

2. Synthetic Resin

1. Natural Resin 

These types of Resin have a natural source. They are obtained from nature. Mostly they originate from the plants. Therefore, it is known as plant Resin. It can be isolated by the whole plant, specific part, or exuded by plants because of injury/incision. Rarely, some natural Resin is obtained from the animal. 

 

Examples of plants from which Resin can be obtained-: Benzoin, ginger, podophyllum, asafoetida, and capsicum.

 

Examples of the animal from which Resin can be obtained:- Shellac or lac, and fossils 

2. Synthetic Resin

These types of Resin are produced in the industry. Synthetic Resins are produced by the curing of the rigid polymer. When they undergo a curing process, they contain reactive end groups like epoxides or acrylates. It can be of various types:

1. Thermoplastic Resins

2. Epoxy Resins

3. Casting Resins

4. Epoxy Resins

5. Ion exchange Resins

6. Acetal Resins

7. Acrylic glass

 

Resin Chemical Nature 

What is in Resin is the most commonly asked question in the polymer Chemistry branch? The answer to this question is, Resin chemically is a complex compound. It is formed by a mixture of various compounds. These are a mixture of essential oils. It can be a mixture of oxygenated products of terpenes (oxygenated hydrocarbons) or it can be a complex mixture of hydrocarbons, acid, ester, and alcohol.

 

They are amorphous or semi-crystalline solids that can be converted into plastic. These chemicals usually have a polymeric or semi-polymeric structure and are either natural or (semi-)synthetic in nature. Before being pelletized, extruded, and moulded into different shapes, they are frequently treated with plasticizers, stabilizers, fillers, antioxidants, and other additives.

Resins are a diverse group of compounds with a vast range of properties. So, let us now look at the different properties of Resin in the coming section.

 

Properties of Resins

• These are transparent or translucent solid or semisolid.

• The specific gravity of Resins is more than water. Therefore, these are heavier than water.

• They generally become soft at heating. On further heating, Resins will be melted.

• Resins generally occur in an amorphous state.

• These are insoluble in water.

• These are soluble in organic compounds like alcohol, volatile oils, and chloral hydrate.

• These compounds are highly enriched with carbon.

• Resins are deprived of nitrogen and oxygen.

• Resins undergo a slow oxidation process in the atmosphere and become dark in color.

 

How is Resin Made?

Based on their formation:

1. Physiological Resin

These types of Resins are formed by the normal metabolism process.

Example – cannabis, podophyllum, and ginger.

2. Pathological Resin

These types of Resin are formed by the result of the wound, injury, or abnormal circumstances. 

Example – benzoin, asafoetida, and guggul.

 

Classification of Resin

Classification of Resin is based on the nature of occurrence with other secondary metabolites. They are classified as below:

1. Oleoresin- 

These are naturally occurring Resin, which is a mixture of Resin and volatile oil. Examples of such types of Resins are capsicum, ginger, and copaiba.

2. Gum Resin- 

These types of Resins are associated with the gum. Examples of such types of Resins are colophony and cannabis. 

3. Oleo Gum Resins- 

These types of Resins are a mixture of volatile oil, gum, and Resin. Examples of such types of Resins are guggul, asafoetida, and myrrh.

4. Balsams Resin- 

These types of Resin are a mixture of benzoic acid and cinnamic acid or esters of these acids. It can occur in free or combined form. Examples of such types of Resins are benzoin, tolu balsam, Peru balsam.

5. Glyco Resin- 

This type of Resin occurs in combination with sugar. These Resins are linked with the sugar molecule by the glycosidic linkage. Examples of such types of Resins are jalap and podophyllum.

 

Natural Resin Uses

• These are used as flavoring agents.

• Natural Resins are used as a carminative agent.

• It is used as an expectorant.

• It is used as a stimulant or diuretic agent.

• It is used as an anticancer drug.

• It shows a cathartic property.

• It is used as an anti-inflammatory property.

• It is also used for bow treatments for instruments like cellos and violins.

 

The Occurrence of Natural Resins

Resins are secreted in specialized structures. It can be either in the internal part or on the surface of different parts of the plant.

1. Resin Cell – Ginger

2. Glandular Hair – Cannabis

3. Schizogenous or Schizolysigenous Duct or Cavities – Pinewood

4. Induced at a Site of Injury / Incision – Benzoin

 

Did You Know?

• Resins are generally distributed in Spermatophyta (seed plants) plants.

• Some Resins can be obtained from the Pteridophyta.

• Resins are considered the end product of metabolism.

Several metallic materials in course of the time develop chemical changes on their surface, if left unused, or stagnant. These changes are known as corrosion. Corrosion is a process that leads metals to a gradual degradation. It will happen on iron and its alloys such as steel. Rusting of iron is one of them. Iron objects react with the oxygen present in the air and develop rust in a humid environment. The other examples of corrosion are tarnish on silver and the blue-green patina on copper. 

Rust is basically an iron oxide. Mostly, red oxide is formed by the redox reaction between oxygen and iron in the presence of air moisture and water. It was researched that surface rust is friable and flaky and does not provide any protection to the iron.  ‘Green rust’ is developed when iron reacts with chloride in the presence of water and oxygen which is mostly found in the underwater iron pillars. 

What is the Chemistry Behind the Rusting of Iron?

The formation of rust takes place in the presence of water and oxygen on iron or some of its alloys. The reaction needs a considerable long time to develop. The formation of bonds between iron atoms and oxygen atoms makes iron oxides. The rusting of iron includes an upsurge in the oxidation state of iron with a loss of electrons. The rust chemical formula can be written as Fe2O3.3H2O (hydrated iron (III) oxide).

Rusting of iron reaction: 4Fe + 3O2 → 2Fe2O3

Fe2O3 reacts with water and forms Fe2O3.3H2O. 

Rust is developed from two different iron oxides that are different due to their oxidation state in the iron atom. These oxides are

1. Iron (II) oxide or ferrous oxide – The oxidation state of iron in this compound is +2 and its chemical formula is FeO.

2. Iron (III) oxide or ferric oxide – in which the iron atom shows an oxidation state of +3. The chemical formula of this compound is Fe2O3.

We all know that oxygen is an excellent oxidizing agent while iron is a reducing agent. So, the iron atoms willingly provide their electrons to oxygen when exposed to it. The rusting of iron involves the process:

Fe → Fe2+ + 2e–

The oxidation state of iron changes due to the oxygen atom in the presence of water.

The ferrous ions get oxidized to ferric ions in presence of moisture and air, also generating hydroxyl ions and yielding ferric hydroxide.

4Fe2+ + O2+ 2H2O →4Fe3+ + 4OH–

Fe3+ +3OH– → Fe (OH)3 

Fe (OH)3 converts into Fe2O3.3H2O. 

Factors that Affect Rusting of Iron

All the chemical reactions of rusting are dependent on the presence of water and oxygen. The rusting of iron can be controlled by restricting the amount of oxygen and water surrounding the metal.

Why is Rusting an Undesirable Phenomenon?

Rusting is known as a great destroyer of things. It can destroy cars and other vehicles, sink ships, fell bridges, spark the fire, and destroy everything that is made up of iron or its alloys.

The entire piece of metal may disintegrate and be turned to rust when left unattended for extended periods. This can cause many problems as iron is used to construct buildings, bridges, automobiles, etc. Rust makes the metal weaker as oxidized metal is weaker than the original metal itself. It also makes the metal brittle and puts it at risk of breaking. 

Iron is also used to make water pipes and storage tanks. If this iron rusts, the pipes can get damaged. They can also increase the amount of iron oxide in the water being transported. Rust also acts as a breeding ground for bacteria. If a person is injured by rusted iron, he/she could be at risk for tetanus. 

How can Rusting be Prevented?

Rusting can be prevented by many methods. One method is to keep iron from corrosion by painting it. The layers of paint resist oxygen and water to form rust on the surface of iron as paint prevents iron from contacting them directly. The iron is protected from corrosion as long as the paint is there. Oil-based paints are hassle-free and the most highly recommended. Alternatively, any organic paint with a 15-25µm thickness may be used to prevent rust.

Alternatively, rusting can be prevented by thermoplastic or a thermoset polymer powder coating on the iron surface. Powder coating is considered superior to paint as it gives a thicker protective layer. Spraying a dry, organic powder onto the iron surface and heating the iron to the melting point of the powder. Once melted, the powder creates an even layer over the iron surface. Common materials used for powder coating include vinyl, polyester, nylon, acrylic, urethane, and epoxy-based organic materials.

Other strategies include iron alloying with other metals. For example, stainless steel is mostly made up of iron with a little amount of chromium. 

In a different strategy, iron is galvanized or zinc-plated. Zinc has a lower reduction potential which enables it to oxidize more easily than iron. Zinc is a more active metal. This process is known as galvanization. The metal (iron) is covered with another metal such as zinc to form a protective layer. Galvanization can be done in two ways:

Hot-dip Galvanization: that involves dipping the iron into a very hot bath of melted zinc 

Electro-Galvanization: Involves using zinc metal as an anode, iron as the cathode, and passing electricity through a zinc solution to apply an even coating of zinc on the iron surface. 

Electro-galvanization is the preferred method of galvanization today as it produces an even coating, unlike the hot-dip method.

Cathodic Protection

An important method to protect iron from rusting is to make it a galvanic cell cathode. This process is known as cathodic protection. It can be used for metals, not only for iron. In this process, iron is connected with a more active metal such as magnesium or zinc. The more active metals have a lower reduction potential. Then, the other metal (iron) behaves as a cathode and does not get oxidized. This process is highly u
seful to the storage of iron tanks underwater when anodes are monitored properly and replaced timely. This process is also used to protect metal parts of water heaters.