CARBON AND ITS COMPOUNDS (PART-2)

 Homologous Series: Series of organic compounds having the same functional group and chemical properties and successive members differ by a CH2 unit or 14 mass units are known as Homologous series.

Homologous series of Alkanes, Alkenes and Alkynes

Characteristic of Homologous Series

• The successive members in homologous series differ by CH2 unit or 14 mass unit.
• Members of given homologous series have the same functional group.
• All the members of homologous series shows similar chemical properties.

Functional Group: An atom or group of atoms present in a molecule which largely determines its chemical properties are called Functional Group.

Nomenclature of Organic Compounds: It is difficult to remember millions of compounds by their individual common name. Thus, to systematize the nomenclature of organic compounds IUPAC (International Union of Pure and Applied Chemistry) has given certain rule which is as follows:

1. Identify the Number of Carbon Atoms in the Compound

S. No	Number of Carbon Atoms	Word Root (-) (Suffix)	Single bond
1.	One carbon atoms (1-C)	Meth	+ ane
2.	Two carbon atoms (2-C)	Eth	+ ane
3.	Three carbon atoms (3-C)	Prop	+ ane
4.	Four carbon atoms (4-C)	But	+ ane
5.	Five carbon atoms (5-C)	Pent	+ ane
6.	Six carbon atoms (6-C)	Hex	+ ane

2. Identify the functional group

S. No.	Functional Group	Prefix	Suffix
1.	Double bond (=)	—	ene
2.	Triple bond (≡)	—	yne
3.	Chlorine (—Cl)	Chloro	—
4.	Bromine (—Br)	Bromo	—
5.	Alcohol (-OH)	—	ol
6.	Aldehyde (-CHO)	—	al
7.	Ketone (-CO-)	—	one
8.	Carboxylic acid (-COOH)	—	oic acid

3. Name the Compounds By Following Order
Prefix + Word Root + Suffix

Chemical Properties of Carbon Compounds: The important chemical properties are as follows:
1. Combustion: The complete combustion of carbon compounds in the air gives carbon dioxide water, heat and light.
CH3CH2OH(l) + O2(g) → CO2(g) + H2O(l) + Heat and light

Carbon burns in air or oxygen to give carbon dioxide and heat and light.
C(s) + O2(g) → CO2(g) + Heat and light

Saturated hydrocarbons burn with a blue flame in the presence of a sufficient supply of air or oxygen.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + Heat and light

In presence of limited supply of air, saturated hydrocarbon forms a sooty flame.

Unsaturated hydrocarbons burn with a yellow smoky flame.

The gas and kerosene stove used at home has inlet for air so that, burnt to given clean blue flame.
Due to presence of small amount of nitrogen and sulphur, coal and petroleum produces carbon dioxide with oxides of nitrogen and sulphur which are major pollutant.

2. Oxidation: Oxidation of ethanol in presence of oxidizing agents gives ethanoic acid.

Oxidizing Agent: Some substances are capable of adding oxygen to others, are known as Oxidising Agent.
Example: Alkaline KMnO4 (or KMnO4—KOH)
Acidified K2Cr2O7 (or K2Cr2O7—H2SO4)
KMnO4 – Potassium permanganate
K2Cr2O7 – Potassium dichromate

3. Addition Reaction: Addition of dihydrogen with unsaturated hydrocarbon in the presence of catalysts such as nickel or platinum or palladium are known as Hydrogenation (addition) reaction.

Catalyst: Substances that cause a reaction to occur or proceeds to different rate without consuming in it are called a catalyst. For example; Ni, Pt, Pd, etc.

Process of converting vegetable oil into solid fat (vegetable ghee) is called Hydrogenation of Oil.
Vegetable oil + H2   Vegetable ghee

Vegetable fats are saturated fats which are harmful for health.

Vegetable oil containing unsaturated fatty acids are good for health.

4. Substitution Reaction: Replacement of one or more hydrogen atom of an organic molecule by another atom or group of the atom is known as Substitution Reaction.

Some Important Carbon Compounds :
Ethanol (CH3CH2—OH): Commonly known as Ethyl Alcohol.
Physical Properties

• It is colourless, inflammable liquid.
• It is miscible with water in all proportions.
• It has no effect on the litmus paper.

Chemical Properties

• Reaction with sodium
  
• Reaction with concentrated H2SO4 (Dehydration Reaction)
  

Dehydrating agent: Substances which removes water from ethanol (alcohols) is known as Dehydrating agent. For example; Cone. H2SO4.
Uses: As solvent, as antiseptic (tincture iodine), as anti-freeze in automobiles.

Ethanoic Acid (CH3COOH): Commonly known as Acetic acid. 5-8% of ethanoic acid in water is called Vinegar. The melting point of pure ethanoic acid is 290 K and hence, it often freezes in cold climate so named as glacial acetic acid.

Physical Properties

• It is a colourless, pungent-smelling liquid.
• Miscible with water in all proportions.
• Turns blue litmus to red.

Chemical Properties
(i) Esterification Reaction: Reaction of ethanoic acid with an alcohol in the presence of a few drops of conc. H2SO4 as catalyst gives a sweet-smelling substance known as Esters, called Esterification reaction.

Esters are used in making perfumes and flavouring agents.                                                       Saponification Reaction: Reaction of esters with sodium hydroxide, gives alcohol and sodium salt of carboxylic acid (soap). This reaction is known as Saponification Reaction.

(ii) Reaction with Carbonates and Hydrogen Carbonates: Ethanoic acid reacts with sodium carbonates and sodium hydrogen carbonates to give rise to a salt, carbon dioxide and water.

• Used as vinegar.
• Used as raw material for the preparation of acetyl chloride and esters

Soaps and Detergents :
Soaps and Synthetic Detergents: Soaps and detergents are substances used for cleaning.
Soap: Soaps are sodium or potassium salts of higher fatty acids, such as Oleic acid (C17H33COOH), Stearic acid (C17H35COOH), Palmitic acid (C15H31COOH), etc. These acids are present in the form of their esters along with glycerol (alcohol containing three hydroxyl groups). These esters, called ‘glycerides’ are present in fats and oils of animal and vegetable origin.
Preparation of Soap: When an oil or fat (glyceride) is treated with sodium hydroxide solution, it gets converted to sodium salt of the acid (soap) and glycerol. The reaction is known as saponification.

Detergents: Chemically, detergents are sodium salts of sulphonic acids, i.e., detergents contain a sulphonic acid group (—S03H), instead^of a carboxylic acid group (—COOH), on one end of the hydrocarbon.

The cleansing action of detergent is considered to be more effective than a soap.
Cleansing Action of Soaps and Detergents: The cleansing action of soaps and detergents follows the same principle.

When soap or detergent is dissolved in water, the molecules gather together as clusters, called micelles. The tails stick inwards and the heads outwards.
In cleansing, the hydrocarbon tail attaches.itself to oily dirt. When water is agitated, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. This gives an opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.

16. Scum: The insoluble precipitates formed by soap molecule when they react with calcium and magnesium ions present in hard water. Due to this, a lot of soap gets wasted and cleansing action gets reduced to a larger extent.