Category: Chemistry Notes PPT

The constituent particles in crystalline solids are arranged in a regular and repeating pattern. The crystal lattice is a diagrammatic representation of three-dimensional arrangements of constituent particles in a crystal, where each particle is represented as a point in space. The atoms in a crystal lattice are packed so closely together that there is very little space between them. As a result, the cubic form of a lattice’s unit cell. There will still be some empty spaces in the cell as we stack the spheres. The arrangement of these spheres must be very effective in order to eliminate these empty spaces. To avoid empty spaces, the spheres should be placed as close together as possible.

The definition of Coordination Number is also related. In a crystal lattice structure, the coordination number is the number of atoms that surround a central atom. As a consequence, there are three directions in which the constituent particles are tightly packed. Let’s take a look at each of them individually.

The following sections discuss close packing in crystals in solids in various dimensions:

Close Packing in One Dimension

Packing in one dimension involves arranging spheres in a row such that neighbouring atoms are in contact. The number of nearest neighbour particles is known as the coordination number. The coordination number is two in the case of one-dimensional close packing.

Close Packing in Two Dimension

A row of closed packed spheres is stacked to create a two-dimensional pattern in two-dimensional close packing. There are two methods for stacking:

Square Close Packing:

In a close packing, the second row can be put exactly below the first row. As a result, if we call the first row a “A” type row, the second row, which is organized identically to the first, is also an “A” type row. Each sphere is in contact with four other spheres in this configuration. As a result, it has a four-coordination number. We note that when the centres of the four closest spheres are joined, a square is formed. In crystalline solids, this type of packing is known as square close packing in two dimensions.

Hexagonal Close-Packing (ABAB Type Arrangement): 

The second row can be staggered below the first row, with its spheres fitting into the depressions of the first row. As a result, if we refer to the first row as an “A” type row, the second row, which is organized differently, can be referred to as a “B” type row. The third-row displays as “A” form once more. The “ABAB” sort of packing is what it’s called. Each sphere is in contact with six other spheres in this configuration. As a result, it has a teamwork number of six. When the centres of the six closest neighbouring spheres are connected, a hexagon is formed. Hexagonal close packing in two dimensions is the name given to this type of solid packing. In contrast to square close packing, it has less free space and thus higher packing efficiency.

Three Dimensional Close Packing

True lattices and structures are formed by packing three-dimensionally close together. They’re created by piling two-dimensional sphere layers on top of each other. This can be accomplished in two ways:

1. Close packing in three dimensions derived from two-dimensional square close-packed layers

2. Close packing in three dimensions derived from two-dimensional hexagonal close packing layers

Three-Dimensional Close Packing from Two-Dimensional Close-Packing in Crystals: 

By putting the second square closed packing exactly above the first, three-dimensional close packing in solids can be created. The spheres are properly positioned horizontally and vertically in this tight packing. Similarly, we can make a simple cubic lattice by stacking more layers one on top of the other. The primitive cubic unit cell is the unit cell of the basic cubic lattice.

Three-dimensional Close Packing from Two-Dimensional Hexagonal Close-Packing in Crystals:

Close packing in three dimensions derived from two-dimensional hexagonal close packing layers

With the support of two-dimensional hexagonal packed layers, three-dimensional close packing can be shaped in two ways:

1. Stacking the second layer on top of the first

2. Stacking the third layer on top of the second

Stacking the Second Layer Over the First Layer

Assume that we take two hexagonal tight-packed layers ‘A’ and position them over the second layer B (because the spheres in both layers are aligned differently) such that the spheres of the second layer are positioned in the depressions of the first layer. When a sphere from the second layer is positioned directly above the void (space) from the first layer, a tetrahedral void is created. We also note octahedral voids at the points where the second layer’s triangular voids are placed next to the first layer’s triangular voids in such a way that triangular space does not overlap. Six spheres surround the octahedral voids.

By Stacking the Third Layer Over the Second Layer

1. By covering tetrahedral voids 

2. By covering octahedral voids

Did You Know?

The spheres of the third layer are aligned directly above the spheres of the first layer in three-dimensional packing. If we give the first layer the letter A and the second layer the letter B, the pattern would be ABAB… and so on. The resulting structure is known as a hexagonal close-packed structure, or HCP.

Spheres are not put with either the second layer or the first layer in this form of packaging. The pattern would be ABCABC if we call the first layer A, the second layer B, and the third layer C (as it is now a separate layer). The resulting structure is also known as a cubic close packed (ccp) structure or a face-centred packed cubic structure (fcc). Metals such as copper and iron, for example, crystallize in the structure. Since each sphere in the system is in direct contact with 12 other spheres, the coordination number in both cases would be 12. The packing is extremely effective, with approximately 74% of the crystal being fully occupied.

Amino acids are organic compounds that contain the functional groups amino (–NH₂) and carboxyl (–COOH), as well as a side chain (R group) unique to each amino acid. Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) are the four essential elements of amino acids, while other elements can be present in the side chains of some amino acids.

In this article standard, sigma amino acid standard and non standard amino acids are discussed in detail.

Standard Amino Acids Definition

What are the standard and non standard amino acids?

The polarity (that is, the distribution of electric charge) of the R group is one of the most useful ways to classify the regular (or common) amino acids.

Given below is the number of standard amino acids and also standard amino acid structure.

Twenty Standard Amino Acids

1. Non-Polar Amino Acid

Glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, and tryptophan are all members of Group I amino acids. These amino acids have either aliphatic or aromatic groups in their R groups. This makes them hydrophobic. Globular proteins fold into a three-dimensional form in aqueous solutions to bury these hydrophobic side chains in the protein interior. 

A. Glycine

Glycine is the only amino acid that is not optically active and was the first to be isolated from a protein, in this case, gelatin (no d- or l-stereoisomers). When introduced into proteins, it is the most unreactive of the -amino acids due to its structural simplicity.

B. Leucine

In 1819, leucine was isolated from cheese, and in 1820, it was isolated in its crystalline form from muscle and wool. It was first synthesized in a laboratory in 1891. Given below is the amino acid standard structure.

C. Alanine

Alanine was first discovered in protein in 1875 and accounts for 30% of the residues in silk. Silk fibres are strong, stretch resistant, and flexible thanks to their low reactivity and clear, elongated structure with few cross-links.

D. Valine

After being isolated from albumin in 1879, the structure of valine was discovered in 1906. Mammalian proteins only contain the l-stereoisomer. Valine can be broken down into simpler compounds in the body, but in people with maple syrup urine disease, a defective enzyme prevents this from happening and can be fatal if left untreated.

E. Tryptophan

The structure of tryptophan was identified in 1907 after it was isolated from casein (milk protein), but only the l-stereoisomer appears in mammalian proteins.

F. Phenylalanine

In 1879, phenylalanine was isolated from a natural source (lupine sprouts) and chemically synthesized in 1882. The human body is normally capable of converting phenylalanine to tyrosine, but in people who have the hereditary disorder phenylketonuria (PKU), the enzyme responsible for this conversion is inactive.

G. Methionine

In 1922, methionine was isolated from the milk protein casein. Methionine is an essential sulfur source for a variety of body compounds, including cysteine and taurine. Methionine prevents fat accumulation in the liver and assists in the detoxification of metabolic wastes and contaminants, due to its sulfur content.

H. Isoleucine

In 1904, isoleucine was discovered in beet sugar molasses. The hydrophobic nature of isoleucine’s side chain plays a key role in deciding the tertiary structure of proteins that contain it.

2. Polar Uncharged Amino Acids

Serine, cysteine, threonine, tyrosine, asparagine, and glutamine are all members of Group II amino acids. This group’s side chains have a wide range of functional groups. Most, however, have at least one atom with electron pairs usable for hydrogen bonding to water and other molecules (nitrogen, oxygen, or sulfur).

A. Serine

Serine was first isolated in 1865 from silk protein. Humans can make serine from other metabolites, such as glycine, but mammalian proteins only contain the l-stereoisomer. Serine is required for the biosynthesis of several metabolites and is frequently required for the catalytic role of enzymes that contain it, such as chymotrypsin and trypsin.

B. Tyrosine

Tyrosine was isolated from the degradation of casein (a cheese protein) in 1846, after which it was synthesized in the lab and its structure determined in 1883. Humans can synthesize tyrosine from phenylalanine.

C. Glutamine

In 1883, glutamine was isolated from beet juice, then from a protein in 1932, and finally chemically synthesized the following year. Glutamine is the most abundant amino acid in the human body and serves a variety of functions.

D. Threonine

In 1935, threonine was isolated from fibrin and synthesized the following year. In mammalian proteins, only the l-stereoisomer appears, and it is relatively unreactive. Although it is involved in a variety of bacterial reactions, its metabolic function in higher animals, including humans, is unknown.

E. Asparagine

The first amino acid to be isolated from a natural source was asparagine, which was purified from asparagus juice in 1806.

F. Cysteine 

Cysteine was first isolated from a urinary calculus in 1810 and from hooves in 1899, and it is abundant in the proteins of fur, hooves, and skin keratin. It was then chemically synthesized, and the structure was determined in 1903.

3. Acidic Amino Acids

Aspartic acid and glutamic acid are the two amino acids in this category. Each one has a carboxylic acid on its side chain, which makes it acidic (proton-donating). The three functional groups on these amino acids can ionize in an aqueous solution at physiological pH, resulting in an overall charge of 1. Aspartate and glutamate are the ionic forms of amino acids.

A. Aspartic Acid

Aspartic acid was discovered in 1868 and is present in animal proteins; however, only the l-stereoisomer participates in protein biosynthesis.

B. Glutamic Acid 

In 1866, glutamic acid was isolated from wheat gluten, and in 1890, it was chemically synthesized. Only the l-stereoisomer is present in mammalian proteins, which humans can synthesize from the natural intermediate -ketoglutaric acid.

4. Basic Amino Acids

Arginine, histidine, and lysine are the three amino acids that make up this category. Each side chain is fundamental (i.e., can accept a proton). At physiological pH, both lysine and arginine have an average charge of +1). Ionic bonds form between the side chains of arginine and lysine, just as they do with aspartate and glutamate.

A. Arginine

When proteins are digested in humans, arginine is formed. The human body will then transform it into nitric oxide, a chemical that relaxes blood vessels.

Arginine has been proposed for the treatment of chronic heart disease, elevated cholesterol, impaired circulation, and high blood pressure due to its vasodilatory effects.

B. Lysine

In 1889, lysine was isolated from the milk protein casein, and its structure was discovered in 1902. Lysine is essential for the binding of enzymes to coenzymes and the proper functioning of histones.

Did You Know?

Non standard amino acids are those that have been chemically modified after being inserted into a protein (a process known as “post-translational modification”), as well as those that occur naturally in living organisms but are not present in proteins. Carboxyglutamic acid, a calcium-binding amino acid residue present in the blood-clotting protein prothrombin, is one of these modified amino acids (as well as in other proteins that bind calcium as part of their biological function). Collagen is the most abundant protein in vertebrates in terms of mass. 4-hydroxyproline and 5-hydroxylysine are modified versions of proline and lysine that make up a significant portion of collagen’s amino acids.

Revising the concept of Standard Amino Acids 

Revising the concept of Standard Amino Acids will not be that difficult. However, it might take a lot of your time if you do not understand the concept properly. To start learning the Standard Amino Acids – Detailed Explanation and FAQs, you will need a reliable study resource that provides you with accurate and detailed explanations of amino acids. Below are some tips to help you in learning the concept of Standard Amino Acids – Detailed Explanation and FAQs: 

• Firstly, you have to go through the textbook explanations of Standard Amino Acids – Detailed Explanation and FAQs to understand what amino acids are and how they work. 

• Once you are done with the textbook, you can refer to revision notes and reference guides to get a better understanding of Standard Amino Acids – Detailed Explanation and FAQs and enhance your knowledge. 

• Try to make your own notes while studying the Standard Amino Acids – Detailed Explanation and FAQs and make a summary of the concept as well. These notes and summary will help you in quick revisions before the final exam. 

• After you have thoroughly gone through the concept of Standard Amino Acids – Detailed Explanation and FAQs, you should start with the questions and problems given in your textbook and reference guides for practice. 

• You should use sample papers and previous year questions papers to pick out the questions based on Standard Amino Acids – Detailed Explanation and FAQs. You can solve these questions and understand the difficulty level of your tests. 

• Use ’s online learning platform to get a deep insight into the concept of Standard Amino Acids – Detailed Explanation and FAQs and ensure an excellent score in the final exam.    

Importance of Learning Standard Amino Acids

The concept of Standard Amino Acids – Detailed Explanation and FAQs is quite important to learn for all the students. This concept teaches you about various amino acids and how they are used in different areas. By understanding the uses of amino acids, you can enhance your knowledge of chemistry and ensure good marks in the exam. Here are some reasons why the Standard Amino Acids – Detailed Explanation and FAQs is important to learn: 

• The Standard Amino Acids – Detailed Explanation and FAQs holds a significant portion of the marking distributions in your exam. By learning this concept, you can ensure an excellent score in your tests and exams. 

• Amino acids play a vital role in building protein and the synthesis of neurotransmitters and hormones. Learning the Standard Amino Acids – Detailed Explanation and FAQs help you understand how amino acids build this protein in your body.  

• By Learning the Standard Amino Acids – Detailed Explanation and FAQs, you will understand which amino acids are good for your health. 

Carbohydrates are a group of organic compounds that occur in living tissues and foods in the form of sugars, cellulose, and starch. The general formula of carbohydrates is [CH_{2}O_{n}]. Just as in water, the ratio of oxygen and hydrogen is fixed in carbohydrates, which is 2:1. It generally breaks down to release energy in humans and animals. Today, we are going to learn about the classification of carbohydrates and their structures.

Carbohydrates Classification

Given below is the classification of carbohydrates in biochemistry.

Types of Carbohydrates – Simple Carbohydrates

The basic type of carbohydrates is simple carbohydrates that are found in natural sugars present in fruits, vegetables, milk, and honey. These carbohydrates are much simpler to study since they have a less complex structure.

Simple carbohydrates consist of only units of monosaccharides, which is why they are the smallest and simplest of all the other types of carbohydrates. Their smaller size plays a vital role in metabolism and digestion in the gastrointestinal tract.

Types of Carbohydrates – Complex Carbohydrates

Complex carbohydrates are an essential source of energy for our body. They give us the sustained fuel that our body needs for carrying out day-to-day activities, for working out, and for even taking rest. Complex carbohydrates often comprise different units of monosaccharides bound together and provide us with long-lasting energy. The complex carbohydrates are classified depending on their hydrolysis behavior. They are divided into three groups as follows.

1. Monosaccharides

2. Disaccharides

3. Polysaccharides

Monosaccharides

Monosaccharides are carbohydrates that cannot be hydrolyzed further for giving simpler units of either a polyhydroxy aldehyde or a ketone. If a monosaccharide consists of an aldehyde group, it is referred to as aldose and if it consists of a keto group then it is referred to as a ketose.

Disaccharides

After the process of hydrolysis, disaccharides tend to yield either two molecules of the same or the different monosaccharides.

1. Two units of monosaccharide are joined by an oxide linkage that is formed when there is the loss of water molecule, and this linkage is referred to as glycosidic linkage.

2. Sucrose is amongst the most common disaccharides that give both glucose and fructose on hydrolysis.

3. Maltose and lactose, often referred to as milk sugar, are also the two kinds of important disaccharides.

4. Maltose contains two α-D-glucose whereas lactose consists of two β-D-glucose that are connected through an oxide bond.

Polysaccharides

1. Polysaccharides consist of longer monosaccharide units that are joined together by glycosidic bonds.

2. Most of these polysaccharides act as storage for food, such as starch. Starch is known to be an important storage polysaccharide in plants.

3. Starch is a polymer of α glucose and has two components, that are amylose and amylopectin.

4. Cellulose is also an essential polysaccharide that is found mostly in plants.

5. It comprises β-D- glucose units that are joined by a glycosidic bond between the C1 of one glucose unit and the C4 of another glucose unit.

Structure of Carbohydrates

Carbohydrates have traditionally been characterized as compounds having the empirical formula [Cn(H_{2}O)m]. Glucose, fructose, and sucrose are popular sugars that suit this formula, however, currently, a carbohydrate is defined as a polyhydroxy aldehyde or polyhydroxy ketone with the traditional formula, a molecule closely similar to it, or oligomers or polymers of such molecules. Because they are water-soluble and difficult to crystallise, they need a different set of abilities to manipulate than traditional “natural products” like terpenes, steroids, and alkaloids.

A “monosaccharide” is a carbohydrate derivative with a single carbon chain; “disaccharide” and “trisaccharide” are compounds with two or three monosaccharide units linked together by acetal or ketal linkages. Larger aggregates with “a few” and “many” monosaccharide units are referred to as “oligosaccharide” and “polysaccharide,” respectively. The divide between “few” and “many” appears to be drawn at roughly 10 units in current use.

By the middle of the nineteenth century, chemists in Europe, particularly in Germany, had discovered a variety of relatively pure carbohydrates such as sucrose, cotton cellulose, starch, glucose, fructose, mannose, and lactose. Emil Fischer produced phenylhydrazine for his University of Munich thesis in 1878. He also found in 1884 that carbohydrates produced crystalline phenylosazone when two phenyl hydrazines interacted with the aldehyde group and the carbon next to it.

Structure of Carbohydrates – Glucose

Glucose is amongst the most important monosaccharides. The two commonly used methods to prepare glucose are as follows.

1. From Sucrose: When sucrose is boiled with dilute acid in an alcohol solution, glucose and fructose are obtained.

2. From Starch: Glucose can also be obtained by the hydrolysis of starch and boiling it with dilute sulphuric acid, at a temperature of 393K, under high pressure.

Glucose is also known as dextrose and aldohexose and is plentiful on earth.

Structure of Carbohydrates – Fructose

Fructose is an essential ketohexose having a molecular formula [C_{6}H_{12}O_{6}]. It consists of a ketone functional group situated at carbon number 2 and contains six carbon atoms in the form of a straight chain. The ring member of fructose is analogous to the compound called Furan and is therefore termed furanose. The cyclic structure of fructose is as follows:

Conclusion

We are all surrounded Carbohydrates are a group of organic compounds that occur in living tissues and foods. The general formula of carbohydrates is [CH_{2}O_{n}]. Just as in water, the ratio of oxygen and hydrogen is fixed in carbohydrates, which is 2:1.

Sulfur dioxide is an inorganic, heavy, colourless, and poisonous gas. It is produced in huge quantities in the intermediate steps of sulfuric acid manufacturing. Sulfur dioxide contains an irritating, pungent odour, familiar as the just-struck match smell. Occurring in nature in solution in the waters of some warm springs and volcanic gases, sulfur dioxide can usually be industrially prepared by the burning in the oxygen of sulfur or air or such compounds of sulfur as copper pyrite or iron pyrite. It has the chemical formula as SO2.

Structure and Bonding

SO2 is a bent molecule with the C2v symmetry point group. A valence bond theory approach by considering simply s and p orbitals would define the bonding in terms of resonance between the two resonance structures.

(Image to be added soon)

The sulfur–oxygen bond holds a bond order of 1.5. There is support for this simple approach that does not invoke the participation of d-orbital. In terms of electron-counting formalism, sulfur atoms contain a formal charge of +1 and an oxidation state of +4.

Occurrence

This is found on Earth and exists in the atmosphere and very smaller concentrations at about 1 ppm.

On the other planets, this compound can be found in different concentrations, the most significant being the Venus atmosphere, which is the third-most significant atmospheric gas at 150 ppm. There, it condenses in the formation of clouds, and is a key component of chemical reactions in the atmosphere of the planet, and contributes to global warming. It also has been implicated as a key agent in the early Mars warming, with concentration estimates in the lower atmosphere as high as 100 ppm, though it exists only in trace amounts. As on Earth, on both Mars and Venus, its major source is thought to be volcanic. The Io-atmosphere, a natural satellite of Jupiter, is 90% sulfur dioxide, and the trace amounts are also thought to exist in the Jupiter atmosphere.

It is thought to exist as a block of ice in abundance on the Galilean moons—as subliming frost or ice on the Io’s trailing hemisphere, and in the crust and mantle of Europa, Callisto, and Ganymede, also possibly in liquid form and reacting readily with water.

Production

Primarily, sulfur dioxide is produced for the manufacturing of sulfuric acid. In the United States, in the year 1979, 23.6 million tonnes of sulfur dioxide were used in the same way, compared to 150 thousand tonnes, which is used for other purposes. Most of the sulfur dioxide is produced by elemental sulfur combustion. Some quantity of sulfur dioxide can also be produced by roasting pyrite and other sulfide ores in the air.

Reactions

Sulfur dioxide is a reducing agent, featuring sulfur in the oxidation state of +4. It is oxidized by halogens to form sulfuryl halides, like sulfuryl chloride. The chemical reaction is given as follows.

SO2 + Cl2 → SO2Cl2

Laboratory Reactions

Sulfur dioxide is considered one of the few common acidic yet reducing gases. Being acidic, this compound turns moist litmus pink, then white (because of its bleaching effect). It can be identified by bubbling it through the dichromate solution and turning the solution to the green from orange (Cr3+ (aq)). It also reduces ferric ions to ferrous.

Sulfur dioxide reacts with certain 1,3-dienes in a cheletropic reaction to produce cyclic sulfones. On an industrial scale, this reaction is exploited for sulfolane synthesis, which is an essential solvent in the petrochemical industry.

(Image to be added soon)

Uses

The overarching and dominant use of sulfur dioxide is in the formation of sulfuric acid.

Precursor to Sulfuric Acid

Sulfur dioxide acts as an intermediate in the formation of sulfuric acid, being converted to sulfur trioxide, and then to the oleum, which can be made into the sulfuric acid. For this purpose, sulfur dioxide is made when the sulfur combines with oxygen. The conversion of sulfur dioxide to the sulfuric acid method is known as the contact process. Many billion kilograms are produced for this purpose annually.

As a Reducing Agent

Sulfur dioxide can also be a good reductant. It is also able to decolourize substances in the presence of water. Particularly, it is useful to reduce bleach for delicate materials such as clothes and papers. Normally, this bleaching effect does not last much longer. Oxygen reoxidizes the reduced dyes in the atmosphere by restoring the colour. Sulfur dioxide is used in the municipal wastewater treatment to treat chlorinated wastewater before release. It also reduces combined and free chlorine to chloride.

Aspirational Applications

Climate Engineering

Sulfur dioxide injections in the stratosphere have been proposed in climate engineering. The sulfur dioxide cooling effects would be the same as what has been observed after the large explosive eruption of Mount Pinatubo in 1991. However, this geo-engineering form would have uncertain regional consequences on the patterns of rainfall, for example, in the monsoon regions.

As a Refrigerant

Being condensed and possessing a high heat of evaporation easily, sulfur dioxide can be a candidate material for refrigerants. Before the chlorofluorocarbons development, sulfur dioxide was used as a refrigerant in home refrigerators.

Fibres are substances used to manufacture materials and fabrics such as cables, wires, clothes, curtains, and bedsheets. They are usually long, thin, and flexible, making them appropriate for manufacturing bendable, strong materials. Some of the most common types of fibres are cotton, silk, jute, linen, nylon, rayon etc. 

During manufacturing, several filaments of fibres come together to build a single product. For example, a cotton towel will require thousands of strands of processed cotton (a type of natural fibre) for its manufacturing. This is typically done in weaving factories.

Although fibres are mainly used in textiles, it should be noted that they have applications in almost all fields. Manufacturing of furniture, automobile, packaging, military devices, aerospace equipment, and other products that are used in day to day lives are some of the most common applications. Fibres are everywhere, making them an important part of modern life.

 

Types of Fibres

Depending upon the origin of the fibre, it is classified mainly into two types:

•  Natural fibres

•  Synthetic fibres

Natural fibre is anything that is procured from a natural source. An example of this type of fibre is cotton which is sourced from cotton seeds that grow on plants. Made of cellulose, an insoluble substance, cotton is fluffy and one of the most common fabrics used today to manufacture clothing materials. Both these types have subcategories. While natural fibres are sourced from vegetables, animals, and plants, synthetic (or manmade) fibres are produced using composition of chemical substances. 

 

Natural Fibres

 

()

 

Natural fibres may be sourced from plants and animals. They are usually processed and turned into yarn, which can then be converted into a product. Natural fibres like cotton are preferred for clothing materials due to their physical properties. They are usually soft and lightweight, making them a sought-after type in textiles.         

Other than textiles, natural fibres are also widely used in non-textile applications. However, it should be noted that natural fibres are thinner and have less strength when compared with synthetic fibres.

Examples of Natural Fibres

Some of the most common types of natural fibres are listed below:

Cotton – a ubiquitous material, it is obtained from cotton seeds and is widely used for textiles. Cotton is soft and lightweight, thus making it a comfortable fibre for clothing materials. All of this has increased its demand in the marketplace

 Silk – obtained from an insect, it is produced from the substance used to form a cocoon

Jute – a stronger fibre among cotton, silk and jute, it is obtained from plants and used to create sacks and other packaging materials.

Wool – obtained from sheep and other furry animals, it is preferred for cloth manufacturing due to its capacity to hold heat. Preferred by people living in regions with cold climate, wool is also a very common clothing fibre

Advantages of Natural Fibres

1. Comfortable to Wear- Clothes made of natural fibre are way more comfortable to wear than clothes made of synthetic fibres, especially in the summer season. In the summer season when the human body releases more sweat, a person needs a breathable fabric to wear which can absorb the excess moisture. Natural fibres like silk and cotton have the properties of allowing enough ventilation in extremely humid and hot weather. These fibres do not stick to the skin and cause allergic reactions like rashes.

2. Exceptional Insulators- Natural fibres have the capacity to trap air in between them, not allowing it to escape into the atmosphere. This air that is captivated in the fabric micro-holes provides warmth and helps maintain a person’s body temperature even in cold, chilling weather conditions. This is the reason why many skiers, trekkers and other people living in cold areas prefer to wear wool or silk.

3.  More Sustainable- As the name suggests, natural fibres are obtained from nature. With the increasing global warming caused due to global warming, the human population needs to use more sustainable clothes, which are also proven to be harmless for the environment. Since these fibres are obtained from plants and animals, they are biodegradable and can be disposed of. Natural fibres can be replaced, recycled or reused time and again in a sustainable way.

 

Disadvantages of Natural Fibres 

1.  More Expensive- Due to having the properties of a great insulator, being more sustainable and more comfortable to wear, natural fibres are generally more expensive than synthetic fibres. Since they are extracted directly from nature, the cost of manufacturing them is often higher than the cost of manufacturing synthetic fibres. The manufacturing process of natural fibres involves taking good and healthy care of the plants and animals that provide these fibres. For example, a pashmina shawl is made of pashmina wool which comes from an indigenous goat living in the high-altitude ranges of the Himalayan mountains. 

2.  Easily Damageable- Natural fibres tend to not last as long as synthetic fibres. They damage easily due to various reasons. For instance, washing cotton or wool excessively can cause wrinkles and shrink of the fabric over time. Alternatively, natural fibres can also become good food for moths and other types of insects if kept exposed to the environment for a long period of time. Since these fibres are made of biodegradable material, various types of insects can feed on them and destroy the clothes completely.

3. Inconsistent Production- The production of natural fibres is sometimes not under the complete control of humans. Nature is independent and does not function according to human’s needs and desires. Its availability is heavily affected by natural disasters and calamities which cause high fluctuations in its production and price.  

 

Synthetic Fibres

 

()

 

Also known as man made or artificial fibres, these are produced through chemical synthesis. Synthetic fibres were first developed in the nineteenth century. One of the main reasons for their creation was the need for stronger fibres that could withstand a lot of pressure. A lot of these fibres have extended use other than textiles.

Examples of Synthetic Fibres: Some of the most common types of synthetic fibres are listed below:

Rayon – a type of semisynthetic material, it is made from combining wood pulp (cellulose), carbon disulphide, and sodium hydroxide. It is used as an imitation of natural fibres like cotton and silk. There are also various subtypes of rayon.

Nylon – one of the most common synthetic fibre, it is entirely made of chemical processes.

Polyester – another common man made fibre, it is made chemically through plant proteins and is widely used in the manufacturing of plastic bottles. Its high strength and longer shelf life are the top characteristics

Several more types of synthetic fibres
are used for non-textile purposes. These are dacron, lyocell, modal, PAN, asbestos, spandex, and polyurethane. Some of these are mixed with natural fibres to create advanced fabrics that have both their characteristics. An example of this method is a stretchable fabric that is used for shirting and other clothing materials. It not only improves the look and feel but also adds to the quality.

 

Advantages of Synthetic Fibres

As mentioned above, synthetic fibres are preferred over natural fibres because of their advantages such as high strength and low making cost. This aligns with the exact need of why manmade fibres were invented in the first place.

In the twenty-first century, synthetic fibres make up for a large part of textiles due to the various advantages attached to them. This includes low cost, higher manufacturing profits, and higher strength that would extend their applications.

Some of these Advantages are Described in Detail Below:

High Strength – Plastic is one of the most popular types of synthetic fibres. It is so because of its series of positive qualities, one of which is strength. Plastic bottles, for instance, are stronger than those made from paper or wood. This same property is what gives synthetic fibres an upper edge over natural fibres

Low Cost and Easy Manufacturing – Manmade fibres can be mass-produced at a relatively lower cost than it takes to produce natural fibres. Moreover, natural fibres require a longer process while man made ones can be produced in a factory in lesser time. For example, cotton not only requires processing in the industry but also the time it needs for the plant to germinate, grow, and bear the seed that contains the cotton

Customization – One of the advantages of synthetic fibres is that they can be engineered to suit the needs. If a particular product requires the fibre to be less susceptible to breaking, it can be engineered through chemical or physical manipulation of the polymer

Most of today’s products, including clothing materials, use amalgamated fibres. As noted above, this allows the fabric or the combined substance to have the properties of both the fibres.

Disadvantages of Synthetic Fibres 

1.  Uncomfortable to Wear- Synthetic fibres can be very uncomfortable to wear as compared to natural fibres. These fibres absorb very little sweat from the body and that is why they are not recommended to be worn in humid weather conditions. Due to their lack of sweat absorbing capacity, they can cause itching and irritation to the sensitive human skin. Since they are made artificially by using chemicals and other synthetic materials, synthetic fibres have proven to cause different allergic reactions. Polyester, for example, can cause skin allergies and should be worn after careful inspection.

2.  Harmful for the Environment- These fibres are manufactured from chemicals and the by-products of petroleum, both of which are non-biodegradable in nature. Due to this, they take decades to decompose in the environment causing serious amounts of land and water pollution. Synthetic fibres also release poisonous gas upon burning that is harmful to humans to inhale and causes excess air pollution.

3. Non-resistant to Fire- The material used to make synthetic fibre- polymer- is easily flammable. It melts and shrinks very easily when it gets in contact with high heat or fire and can stick to the skin of the person wearing this synthetic cloth. Therefore, it is advised to avoid wearing any synthetic clothes, especially acrylic fabric, during cooking or doing any activity that involves the use of fire.

Carboxylic acids are compounds containing the carboxyl functional group in their molecules. The carboxyl group is made up of carbonyl and hydroxyl groups and therefore, the name carboxyl is derived from carbo (from carbonyl) and oxyl from the hydroxyl group. The carboxylic acids may be aliphatic or aromatic depending upon whether the -COOH group is attached to the aliphatic alkyl chain or aryl group respectively.

The functional groups that consist of a Carbonyl Group (C=O) along with a hydroxyl group (O-H) which is attached to the same carbon atom are known as carboxyl groups. The formula for Carboxyl Groups is-

-C(=O)OH

Acids with the presence of one carboxyl group are termed carboxylic acids and since they are proton-donors, they are also known as Bronsted-Lowry acids. Acids with the presence of two carboxyl groups are known as dicarboxylic acids and the ones with the presence of three carboxyl groups are known as tricarboxylic acids.

Salts and esters of carboxylic acids are known as carboxylates.

Though the IUPAC nomenclature of carboxylic acids is ‘oic acids’ in the suffix, ‘ic acids’ is used more commonly.

Qualitative Test for Carboxylic Acid

The following tests are performed for the identification of carboxylic acid.

1. Action with Blue Litmus

All carboxylic acids turn blue litmus red.

Procedure-

• Place the droplet of the liquid, solid or crystal on a moist blue litmus paper and observe the colour change.

• If the red colour changes to blue, it indicates the presence of a carboxylic group.

2. Action with Carbonates and Bicarbonates

Carboxylic acids decompose carbonates and bicarbonates evolving carbon dioxide with brisk effervescence. 

Carboxyl groups react with sodium hydrogen carbonate releasing carbon dioxide gas which can be identified by the effervescence produced. To distinguish carboxylic acids from phenols, this test can be used.

[RCOOH + NAHCO_3 rightarrow RCOONa + Co_2 uparrow + H_20]

Procedure-

• Take one ml of organic liquid in a test tube and add a pinch of sodium bicarbonate [(NaHCO_{3} )] to it.

• If carboxylic acid is present in the organic compound, a brisk effervescence is observed.

3. Carboxylic Acid NaHCO3 Mechanism

()

The reaction of carboxylic acids with aqueous sodium carbonate solution leads to the evolution of carbon dioxide producing brisk effervescence. However, most phenols do not produce effervescence with an aqueous solution of sodium bicarbonate. Therefore, this reaction may be used to distinguish between carboxylic acids with sodium bicarbonate or sodium carbonate, the carbon dioxide evolved comes from Na₂CO₃ or NaHCO₃ and does not form a carboxyl group.

4. Formation of Ester

When carboxylic acids are heated with alcohols in the presence of concentrated sulphuric acid and hydrochloric acid, esters are formed. The reaction is reversible and is called esterification.

Carboxylic acids react with alcohol when there is a presence of sulphuric acid to form an ester that has a fruity smell.

Procedure-

• To 0.1 g of the organic compound add 1 ml ethyl alcohol and one or two drops of concentrated sulphuric acid in a test tube. After heating the mixture in a water bath for about five minutes, pour it into a beaker that has water. If a fruity smell is observed, it indicates the presence of the carboxyl group in the organic compound. 

[RCOOH + C_2H_5OH rightarrow COOC_2H_5 + H_2O]

()

5. Fluorescein Test

This test is used for the identification of the dicarboxylic group. When the dicarboxylic compound is heated, it produces acid anhydride. This anhydride reacts with resorcinol in the presence of Conc. H₂SO₄ and produces a fluorescent dye. 

Procedure-

• Take a small amount of organic compound and heat it with resorcinol and one or two drops of concentrated sulphuric acid in a clean and dry test tube. 

• After a few minutes, the solution turns dark-brown and a liquid is formed.

• Add a few drops of this solution to a dilute NaOH solution.

• If the solution turns red with green fluorescence, it indicates the presence of dicarboxylic acid.

6. Reaction with FeCl₃

Some carboxylic acids give precipitates when they react with iron trichloride. For example, acetic acid gives puff coloured precipitate.

Did You know?

• Methanoic acid is used in leather tanning

• Methanoic acid is used as an antiseptic.

• Benzoic acid and some of its salts are used as urinary antiseptics.

• Carboxylic acid esters are used in perfumery.