Q. 564.4( 14 Votes )

Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction

Answer :

(a) Hydrogenation reaction: The reaction which is commonly used in the conversion of vegetable oils to fats is called hydrogenation reaction. During this reaction, hydrogen is added to unsaturated hydrocarbons. This is an addition reaction which takes place in the presence of catalyst such as palladium or nickel. Catalysts are compounds used to speed up the rate of a reaction without being eaten up during the process. When the hydrogen molecule reacts with an unsaturated hydrocarbon, double bond changes to a single bond. This can be shown by following equation.

A simple hydrogenation reaction can be represented as:

H2C=CH2+H2CH3CH3H2C=CH2+H2CH3CH3

alkene + hydrogen = alkane

Vegetable oils are commonly called polyunsaturated because there are several double bonds in it. Vegetable oils may be converted from liquids to solids by the hydrogenation reaction. Hydrogenated fats and oils are common ingredients in many foods. They are used to extend the longevity of a food item and retain the food flavor for a longer time.

(b) Oxidation reaction: Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. The opposite process is called reduction, which occurs when there is a gain of electrons during a reaction by a molecule, atom or ion. Metals such as sodium, magnesium, and iron are easily oxidized.

After oxidation, properties of an atom or compound change. For example, when an iron undergoes oxidation, it losses electrons. Unoxidized iron is a strong, while oxidized iron is a weak and brittle.

The following equation shows an oxidation reaction.CH3CH2CH2OH + alkaline KMnO4 CH3CH2OOH

(c) Substitution reaction: A substitution reaction is a reaction in which an atom or a group of atoms replaces other atom or atoms in reactants.

There are two types of substitution reactions: nucleophilic and electrophilic. In nucleophilic reactions, the new atom is electron-rich, while in electrophilic reactions, the new atom is electron-deficient.

CH3Cl react with a hydroxy ion (OH-) to produce CH3OH and chlorine. This substitution reaction replaces the chlorine atom on the original molecule with the hydroxyl ion.

The following equation is an example of substitution reaction.CH4 + Cl2 + sunlight CH3Cl + HCl

(d) Saponification reaction: Soaps are made by the process of saponification. Soaps are sodium or potassium salts of long chain fatty acids. When triglycerides in fats react with aqueous NaOH or KOH, they are converted into soap and glycerol. This is called saponification or alkaline hydrolysis of esters.

CH2COOC2H5 + NaOH CH3 COONa + C2H5OH

(e) Combustion reaction: Combustion reaction occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water. It is usually accompanied by the production of heat and light. Combustion involves a reaction between any combustible substance and an oxidizing agent to form an oxidized product.

The following equation is an example of combustion.CH4 + 2O2 CO2 + 2H2O + Heat and light

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