NEET Chemistry Notes Redox Reactions – Redox Reactions

NEET Chemistry Notes Redox Reactions – Redox Reactions

Redox Reactions

Redox Reactions

The reaction, which involves oxidation and reduction as its two half reactions is called redox reaction. A redox change occurs simultaneously.

Types of Redox‘Reactions

These are of three types as follows:

•  Intermolecular Redox Reactions

In such redox reaction molecule of one reactant is oxidised whereas, molecule of other is reduced.

These are further divided into two types:

Combination reactions in which two or molecules (in their zero oxidation state) combine together and one gets oxidised while the other gets reduced.

Displacement reactions in which an atom or ion in a compound is replaced by an atom or ion.
These are further divided into two types:

• Metal displacement reactions in which metal is displaced.
  
• Non-metal displacement reactions in which non-metal is displaced.
  
  Intramolecular Redox Reactions

Which involve oxidation of one element of a compound as well as reduction of other element of the same compound. Decomposition reactions are also intramolecular redox reactions, but to be a redox reaction, it is essential that one of the products of decomposition must be in the elemental state,
e.g.
Autoredox or Disproportionation Reactions

Which involves oxidation and reduction of the same element,
e.g.

Balancing of Redox Reactions

Redox reactions can be balanced through
ion electron method
oxidation number method.

• Ion Electron Method

The method involves the following steps:

• Write redox reaction in ionic form.
• Split redox reaction into oxidation half and reduction half reactions. Balance atoms of each half reactions by using simple multiples. For balancing H and O, add H⁺ ion and H₂0 to the appropriate sides, similarly add OH^– and H₂0 to the appropriate sides. Balance the charge on both the sides and multiply one or both half reactions by suitable number to equalise number of electrons in both equations. Add the two balance half reactions and cancel common terms.
• Oxidation Number Method

The method involves the following steps:

• Assign oxidation number to the atoms in the equation and write separate equations for atoms undergoing oxidation and reduction.
• Find the change in oxidation number in each equation and make the change equal in both the equations by multiplying with suitable integers. After adding both the equations complete the balancing (by balancing H and O).

Redox Titrations

The redox titrations is a type of titration based on a redox reaction between the analyte and titrant. Redox titration may involve the use of a redox indicator and or a potentiometer.

Types of Redox Titrations

The different types of redox titrations are given below:

Potassium Permanganate Titrations

In these titrations, KMn0₄ is self-indicator.

Potassium Dichromate Titrations

In which, the satne reducing agents listed above are directly titrated against K₂Cr₂0₇ in acidic medium,
e.g.
In this case, diphenylamine is the indicator.

Ceric Sulphate Titrations

The indicators used are diphenyl amine or diphenylbenzidine.

Sodium Thiosulphate Titrations

Titration in which sodium thiosulphate is a reducing agent and titrated against iodine.

These are of two types:

•  Iodimetric Titrations which involves direct use of iodine as the oxidising agent, using starch as an indicator,
  e.g.
• Iodometric Titrations in which oxidising agents such as KMn0₄,K₂Cr₂0₇ etc., are treated with KI. In this reaction,  I₂ is liberated quickly, which is titrated against sodium thiosulphate solution using starch as an indicator,

e.g.

ChemistryPhysicsBiology