WBBSE Class 10 Physical Science Notes Chapter 8.6 Organic Chemistry

Comprehensive WBBSE Class 10 Physical Science Notes Chapter 8.6 Organic Chemistry can help students make connections between concepts.

Organic Chemistry Class 10 WBBSE Notes

Organic Chemistry : All carbon containing compounds except oxides of carbon, metal carbonates, bicarbonate, hydrogen cyanide and metallic cyanides are organic compounds and the chemistry of organic compounds is known as organic chemistry.

Organic compounds is a separate branch because organic compounds:

• are large in number
• show isomerism
• are soluble in non-polar solvents
• have complex structures
• are bad conductors
• show catenation
• are made from small number of elements.

Role of organic compounds in life process : Organic compounds are intemately related to our daily life. In order to maintain the life process of our body the following process are required.

• Intake of nutritional food for the growth the living body.
• For repairing the depreciation of health.
• Mobility
• Reproduction

All these are fulfilled almost by all organic materials.

(i) The main ingredients in our food chart are classified of three types : carbohydrates (e.g. rice, wheat, sugar etc.), proteins (e.g. milk, fish, egg etc.) and fats (e.g. milk, oil, butter etc.)

(ii) These food materials are ultimately converted to single organic compounds in different metabolic process with the help of enzymes in our body.

(iii) Vitamin, an organic compound plays indirectly a very important role for maintaining the growth of our health.

(iv) For the translation and mobility of the animals, energy which is required is stored in our body. This energy is associated in an organic compound. This is known as ATP (adenosine triphosphate).

(v) Haemoglobin which is an organic compound an oxygen carrier supplies oxygen in the body.

Biomoleculcs: The molecules of compounds like carbohydrates, amino acids, proteins, vitamins, fats, RNA, DNA etc. which are essential for the continuation of life processes of biological species like plants and animals (including human beings) are known as biomolecules.

Some essential biomolecules are :

(i) Carbohydrates : These molecules are composed of carbon, hydrogen and oxygen. General formula of it is C_n(H₂O)_n. Carbohydrates. are the class of compounds that include polyhydric aldehydes, polyhydric ketones and large polymeric molecules that can be broken down to polyhydric aldehydes and ketones.

Carbohydrates which contain aldehyde groups are called aldose and the carbohydrate containing keto groups are called ketose.

Carbohydrates are mainly of three types :

(a) Monosaccharides : These are the simplest form and are not hydrolysed, e.g. glucose, fructose etc.

(b) Oligosaccharides: During hydrolysis they form fixed number (2-10) of more saccharides.

(c) Polysaccharides: These are the natural polymer of large number of mono saccharides. It has general formula (C₆H₁₀O₅)_n. e.g. starch, cellulose etc.

(ii) Proteins: Another class of compounds essential for living being are proteins. They contain carbon, hydrogen, oxygen and nitrogen. Proteins are consumed daily from our diet. During hydrolysis of proteins by acid, base or enzyme amino acids are produced.
Proteins are of three types :
(a) Simple protein
(b) Conjugated protein
(c) Derived protein.

(a) Types of simple protein :

• Albumin: This type of protein can be isolated from egg, milk, wheat, serum etc.
• Globulin: Proteins that are isolated from egg yolk, tissues, belong to this class of protein.
• Glutemin: This type of protein is present in wheat, rice etc.
• Protamin: This type of protein is present in wheat, barli etc.

(b) Conjugated protein : Examples of this type of protein are : nucleo protein, chromoprotein, glycoprotein, phosphoprotein, lipoprotein, metalloprotein.

(c) Derived protein : This type of proteins are available by the partial hydrolysis of protein of very high molecular weight by acid, base or enzyme to simpler protein.

(ii) Fats: Fats are composed of carbon, hydrogen and oxygen. These are made of glycerol and fatty aids. Fats may be of animal or vegetable origin.

Animal fats are found in : milk, cheese, butter, eggs, meat and oily fish.

Vegetable fats are found in : walnut, almonds, groundnut and coconut, mustard seeds, seasame seed etc.

Fat is a concentrated source of energy.

(iv) Vitamins: Vitamins are organic compounds containing carbon, hydrogen, oxygen and sometimes nitrogen and sulphur. Vitamins are necessary to carry out many vital processes. Their absence or deficiency causes many ailments and impairs the healthy living oi human being.

(v) Amino acids: Proteins are made of amino acids. These are the essential for living beings. Amino acids are the class of compounds containing amino group and carboxylic acid group. 1

Amino acids are of three types :

Neutral amino acids : Amino acids containing the same number of amino and carboxylic acid groups are called neutral amino acids. These have one -NH₂ group and one -COOH group. Total number  of amino acids in this group is 19. e.g. glycine (NH₂CH₂COOH), alanin [CH₃CH(NH₂)COOH] etc.

• Basic amino acids : This type of amino acids have two -NH₂ groups and one-COOH group, e.g. lysine, histidine etc.
• Acidic amino acids : This type of amino acids have two -COOH groups ’• and one -NH_Z group, e.g. aspartic acid, glutamic acid.

The essential amino acids are :

• Valine
• Lucine
• Iso-lucine
• Phenylalanine
• Threonine
• Methionine
• Argenine
• Lysine
• Histidine
• Tryptophan.                                                                                                              ¹

DNA (Deoxyribo nucleic acids): It is found in nucleus, mitochondria and chloroplast of the body cells. James Watson and Francis Crick were able to establish the structure of DNA in 1953. DNA molecule is double helical in nature. It contains three different chemical compositions.

• Phosphoric acid
• Deoxy ribose
• Pyridine like base adenine and guanine, pyrimidine like base thymine and cytonine.

DNA has two strands of polynucleotides coiled around each other by hydrogen; bond in the form of double helix.

Function of DNA :

• Transmission of herediatary characteristics.
• Biosynthesis of proteins.

The genetic information for the cell is preserved in the sequence of this base in the DNA molecule. When a cell divides, DNA molecules replicate and make exact copies of themselves so that daughter cell will have identical DNA to that of parent cell.

RNA (Ribonucleic acid): RNA molecule is single stranded, containing 1 ribose, phosphoric acid and uracil as the nitrogenenous base. RNA plays a very Vital role in life process. RNA carries the message of DNA and acts accordingly.

Type of RNA : (a) mRNA (b) tRNA (c) rRNA. RNA(tRNA, mRNA) helps synthesis of polypeptides, the intermediates of proteins.

Bonding In organic compounds Electronic configuration of carbon shows that the number of electrons available in the outermost orbit is 4. The outermost electrons can only be capable to form covalent bond by sharing and pairing of its electrons with that of other element. So, valency of carbon becomes 4.

Catenation : The property by virtue of which carbon forms covalent linkage amongst them to form stable carbon chains is knoun as catenation. Catenation is an unique property of carbon. As a result of catenation, carbon can form innumerable chemical species with the supplement in various ways by the necessary addition of other elements like H, O, N, P, S, halogens etc.

Difference between organic and inorganic compounds :

Organic Compounds	Inorganic Compounds
(i) Catenation property of carbon atoms and its effect : The catenation property of carbon atoms among themselves and other atoms gives rise to limitless number of organic compounds with strain chains and rings of carbon atoms.	(i) Due to absence of catenetion property of its atoms, the number of inorganic compounds formed by the rest erf the elements in not so large.
(ii) Class similarity : Organic compounds can be easily classified into different groups with certain similar characteristic properties.	(ii) In organic compounds cannot generally be classified into such groups with similar characteristics.
(iii) Thermal stability : Organic compounds are in general, thermally unstable and decompose at higher temperature.	(iii) These are more or less thermally stable., These can tolerate comparatively higher temperatures without decomposition.
(iv) Bonding: Organic compounds are formed through covalent bonding in their molecules.	(iv) These compounds are generally formed by eledrovalent or ionic bonding in their molecules.
(v) Melting and boiling points: As these compounds are covalent in nature, so they have comparatively lower melting and boiling points.	(v) As these compounds are ionic in nature, so they have high melting and boiling points.
(vi) Solubility: These are soluble in organic solvents like alcohol, ether, benzene etc. but generally insoluble in water.	(vi) These are soluble in ionising solvents like water but are generally insoluble in organic solvents.
(vii) Structural characteristics: They have widely varying structural forms, from simple chain structure to complex ring.	(vii) They have mostly simple structure.
(viii) Isomerism: Different types of isomerism often occur in organic compounds.	(viii) Isomerism is practically unknown in inorganic compounds.
(ix) Electrolytic character: These are generally non-electrolytes	(ix) Inorganic compounds are general electrolytes.

Classification of organic compounds :

Functional group : The groups which are responsible to characterise the compounds are Known as functional group.

Homologous series : It is a group of compounds in which the various members have similar chemical properties, possess the same functional group and can be represented by the same general formula. The different members of a homologous series are called homologous and the phenomenon is called homology.

Constitutional or Structural Isomerism : The phenomenon in which two or more different compounds obviously having different physical and chemical properties possess the same molecular formula but different molecular structures due to the arrangements of the constitutional or structural isomerism.

Types of structural isomerism : Three types

(a) Chain isomerism; The compounds of the same class, with the same molecular formula, have chain isomerism due chain carbon atoms.

(b) Position isonierism : The compounds of the same dass, with the same molecular formula, have position isomerism due to the position of functional groups.

(c) Functional group isomerism : The compounds of the same class, with the same molecular formula, have functional group isomerism due to different functional groups.

Hydrocarbons : Hydrocarbons are organic compounds containing only carbon and hydrogen atoms in their molecules.

Types of hydrocarbons: Hydrocarbons are divided into two classes, namely

• Saturated hydrocarbons
• Unsaturated hydrocarbons.

Alkane : Open chain saturated hydrocarbons are known as alkanes. General formula of these compounds are : C_nH_2n+2 (n = integers)

Carbon atoms of these compounds are linked by single covalent bonds. Hy­drogen atoms of these compounds are also linked to one or more carbon atoms by a single covalent bonds.

Saturated hydrocarbon molecules do not contain any formal functional group and as such exhibit very little chemical activity. These are therefore known as paraffins.

Methane: Methane is the first member of the hydrocarbons of the alkane series. It is a colourless gas with molecular formula CH₄.

Source:

(ii) Main source of methane is the natural gas. It is formed in nature in bio­logical decay of plants of swamps and marshes. Methane is called marsh gas. A little phosphine (PH₃) and phosphorous dihydride (P₂H₄) accompany the methane gas and make it spontaneously inflammable. So, it often burns with flashes of flame over marshes. This is well known as ‘will-O-the-wisp’. It is just a natural phenomenon.

Chemical properties:
(i) Burning of methane: It burns in air or oxygen when ignited, and is oxidised to carbon dioxide and water with the evalution of heat.
CH₄+2O₂ = CO₂ + H₂O + 213 kcal/ molecule.

(ii) Substitution reaction : It undergoes substitution reaction. The first step of the reaction is :

Methane: A green house gas: Like carbon dioxide, water vapour etc. methane is known as a green house gas (contribution 19%) because it is capable to absorb visible light from sun-rays and keep the earth surface and its surrounding warm.

Uses of methane:

• It is used as a domestic and industrial fuel by burning in gas-stoves. Almost 40% by volume of methane is present in coal gas.
• It is used in the large-scale production of carbon black which is largely
  used for making printers’ ink, paints, typewriter, ribbon, motor tyres etc.
• It is now used as a source of hydrogen for the synthesis of NH₃.
• It is used for the manufacture of methanol, chloromethane, chloroform etc.

Alkene: An alkene is an unsaturated aliphatic hydrocarbon with a double bond in-between two adjacent carbon atoms of its molecule.

General formula of alkene : C_nH₄ (where n is an integer)

Ethylene [or, Ethene]
The molecular formula of ethylene is C₂H₄ which can be written as CH₂ = CH₂.
It i colourless gas.

Source :
(i)

(ii) It is present in very small amount in coal gas.
(iii) Natural gas rich in methane when ignited at 1400°C — 1500°C at normal pressure, acetylene is obtained after cooling.

Chemical reaction :
(i) Addition reaction with hydrogen:

(ii) Addition reaction with bromine :

Uses of acetylene :

• As an illuminant acetylene is used in acetylene lamp.
• It is used as an oxyacetylene flame 2700°C, for cutting and welding iron plates and sheets.
• It is used for the preparation of acetaldehyde, acetic acid, ethyl alcohol, acetone etc.
• Acetylene is used for the preparation of weston, a solvent used in industry.
• It is used for the preparation of synthetic rubber and plastics.
• It is used as an anaesthatic agent.

Polymer : There are some organic molecules of low molecular weight, a large number of which join with one another repeatedly to produce a very big molecule of high molecular weight. The small molecules are known as monomers and the resulting large molecules are known as p tymers.

Some common polymers :

Hazards of using polymer materials in our environment :

• Polythene, PVC, synthetic rubber after use are left anywhere else. Tyre used in the wheel of a vehicles are also thrown in the dustbin or these are burnt out. These materials have no natural decay in the soil by bacteria.
• As a result there is a dumping of plastic materials and creates an environ­ment pollution.
• It destroys the soils where it is dumping.
• The plastic materials left in hills and mountain, is the cause of landslide.
• Tyre prepared from synthetic rubber when left in air produces free radicals in presence of sunlight which is cancer producer.

Possible alternatives to avoid the hazards :

• To get relief from these, limited uses are desirable
• Now-a-day some reagents are added to plastic materials so that they would not create any problem or hazard to mankind.
• Bags made to cloth, paper, jute should be used instead of polythene bags.

IUPAC (International Union of Pure and Applied Chemistry, 1957) nomenclature simple organic compounds :

Polymerisation: The process or technique through which monomer units combine to give a polymer is known as polymerisation.

Biodegradable polymers : The polymers that can be dissociated into small segments enzymes (produced by microorganisms) are called biodegradable polymers.

Example :
(i) PHBV (poly β-hydroxy butyrate co-β-hydroxy-valerate)

LPG (Liquified Petroleum Gas) : In refinning the crude petroleum, the gaseous products thus obtained the hydrocarbons of lower molecular weight after purification of these gaseous mixtures if there are cooled at hith pressure and low temperature, these are all condensed to liquidand. The liquid is known as Liquified Petroleum Gas (LPG).

Types of LPG :

• Heavier grade LPG (80-90%) : C₄-hydrocarbon (Butane, Isobutane, butene)
• Lighter grade LPG (90%) : C₃ hydrocarbon (Propane and propene, 10% C₄-hydrocarbon (Butane and butene) 2% Ethane and ethylene.

Calorific value : Amount of heat energy produced by the complete com­bustion of one gram of the fuel is known as its calorific value.
Calorific value of LPG ; 29500 kcal/m³

CNG (Compressed Natural Gas):
It is compressed natural gas. It contains mainly methane. It has calorific value 21300 Btu/Ib

Uses of Ethanol:

• Ethanol (C₂H₅OH) is used for drinking purpose.
• Ethanol is widely used as a solvent.
• Ethanol burns of give carbon dioxide and water and thus can be used as fuel.
• Ethanol is used as antifreeze.

Physical properties of Ethanol :

• It is colourless liquid having a sweet smell.
• It is highly soluble in water.
• It is volatile and inflammable.
• It is neutral and it does not change the colour of litmus solution.

Reaction of Ethanol :

(i) Reaction with sodium (active metal): Ethanol reacts with sodium, to form sodium ethoxide and hydrogen.
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

(ii) Reaction of ethanol with cone. H₂SO₄ for dehydration :
Ethanol reacts with cone. H₂SO₄ at about 170°C to form ethylene.

Uses of acetic acid (CH₃COOH)

• It is used as an aid in cooking and for making pickles as also a preservative of fish, meat, vegetable etc. as vinegar (6-8% water solution of acetic acid)
• It is used to prepare white paint.
• It is used to concentrate the latex of leather.

Reactions of acetic acid :

(i) Reaction of acetic acid with NaHCO₃ : During reaction of acetic acid with NaHCO₃, sodium acetate, carbon dioxide and water are produced.
CH₃COOH + NaHCO₃ → CH₃COONa + CO₂↑+ H₂O

(ii) Reaction of acetic acid with NaOH : Acetic acid reacts with NaOH to form sodium acetate and water.
CH₃COOH + NaOH → CH₃COONa + H₂O

(iii) Reaction of acetic acid with C₂H₅OH : This reaction is called esterifi­cation. During this reaction ethyl acetate and water are produced.

Toxicity of Methanol : Methanol has a high toxicity in human. If as little as 10 mL of pure methanol is ingested, for example, it can break down into formic acid, which can cause permanent blindness by destruction of the opti nerve and 30 mL is potentially fatal, although the median lethal dose is typically 100 mL. Toxic effects take hours to start and effective antidotes can often prevent permanent damage.

Methanol is toxic by two mechanisms. First methanol (whether it enters the body by ingestion, inhalation or absorption through the skin) can be fatal due to its CNS depressant properties in the same manner as ethanol poisoing. Second, in a process of toxication, it is metabolized to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver.

Methanol is converted to formal­dehyde via alcohol dehydrogenase (ADH) and formaldehyde is converted to formic acid (formate) via aldehyde dehydrogenase (ALDH). The conversion to formate via ALDH proceeds completely, with no detectable formaldehyde remaining.

Formate is toxic because it inhibits mitochondrial cytochrome C oxides, causing the symptoms of hypoxia at the cellular level, and also caus­ing metabolic acidosis, among a variety of other metabolic disturbances. So methanol is highly toxic and causes blindness insanity and even death. Ethanol is non-toxic but when drunk, it produces physiological effect and disturbs the brain activities.

Denatured spirit : Alcohol used for making beverages is highly taxed but the ethyl alcohol supplied to the chemical laboratories and industries is very cheap.

To make it unfit for drinking purposes, industrial alcohol is mixed with poisonous substance like methanol, pyridine etc. The process is known as denaturing and the product is called denatured alcohol. The ethylalcohol mixed with the methanol is called methylated spirit.