Reduced and oxidized

Aug 26, 2022, 16:45 IST

Concept of Reduced and oxidized

Chemistry deals with varieties of matter and change of one kind of matter into the other. Transformation of matter from one kind into another occurs through the various types of reactions. One important category of such reactions is Redox Reactions. These reactions find extensive use in pharmaceutical, biological, industrial, metallurgical and agricultural areas.

What is Oxidation- Loss of electron is known as Oxidation.

What is Reduction- Gain of electron is known as Reduction

Oxidizing and reducing agents 

Substances that oxidized is called reducing agent and substances that reduced is called oxidizing agent.

Important reducing agents :All metals, (ex. Na, Zn, Fe, Al etc), a few nonmetals (ex. C, H2, S, P etc.) Hydra acids (HCl, HBr, HI, H2S etc), Metallic hydrides (NaH, LiH, CaH2 etc). Organic compounds like HCOOH, (COOH)2 and tartaric acid and their salts, aldehydes, alkanes etc.

Lithium (Li) is the strongest reducing agent in solution, Cesium is the strongest reducing agent in absence of water.

Substances which act as oxidising as well as reducing agents are :

H2O2, SO2, H2SO3, HNO2, NaNO2, Na2SO3, O3 etc. Such a molecule is said to autooxidise and the process (reaction) as autooxidation or disproportionation.

 Types of Redox Reactions

1.  Combination reaction: A combination reaction may be denoted in the manner:

A + B → C

Either A and B or both A and B must be in the elemental form for such a reaction to be a redox reaction. All combustion reactions, which make use of elemental dioxygen, as well as other reactions involving elements other than dioxygen, are redox reactions. Some important examples of this category are:

2.  Decomposition reaction: Decomposition reactions are the opposite of combination reactions. In this, the breakdown of a compound into two or more components at least one of which must be in the elemental state. Examples of this class of reactions are:

3. Displacement reaction: In a displacement reaction, an ion (or an atom) in a compound is replaced by an ion (or an atom) of another element. It may be denoted as:

    X + YZ → XZ + Y

Displacement reactions fit into two categories: metal displacement and non-metal displacement.

a)    Metal displacement: A metal in a compound can be displaced by another metal in the uncombined state. A few such examples are:

b)    Non-metal displacement: The non-metal displacement redox reactions include hydrogen displacement and a rarely occurring reaction involving oxygen displacement.

 All alkali metals and some alkaline earth metals (Ca, Sr, and Ba) which are very good reductants, will displace hydrogen from cold water.

Less active metals such as magnesium and iron react with steam to produce dihydrogen gas:

Many metals, including those which do not react with cold water, are capable of displacing hydrogen from acids. Example:

4. Disproportionation reactions: A redox reaction in which a same element present in a particular compound in a definite oxidation state is oxidized as well as reduced simultaneously is a disproportionation reaction. It is a special type of redox reactions. One of the reactants in a disproportionation reaction always contains an element that can exist in at least three oxidation states. The element in the form of reacting substance is in the intermediate oxidation state and both higher and lower oxidation states of that element are formed in the reaction.

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