Plus One Chemistry Notes Chapter 8 Redox Reactions is part of Plus One Chemistry Notes. Here we have given Kerala Plus One Chemistry Notes Chapter 8 Redox Reactions.
|Text Book||NCERT Based|
|Chapter Name||Redox Reactions|
|Category||Plus One Kerala|
Kerala Plus One Chemistry Notes Chapter 8 Redox Reactions
Redox reactions are combinations of oxidation and reduction reactions.
Any process which involves:
- addition of oxygen or electronegative radical.
- removal of hydrogen or electropositive radical.
eg., Addition of oxygen
C + O2→ CO2
Addition of electronegative radical
2FeCI2 + Cl2 → 2FeCI3
Removal of hydrogen
H2S + Br2 → 2HBr + S
Removal of electropositive radical
2KI + H2O2 → 2KOH + l2
Any process which involves
- addition of hydrogen or electropositive radical.
- removal of oxygen or electronegative radical
eg., Addition of hydrogen
Br2 + H2S → 2HBr + S
Addition of electropositive radical
2HgCI2 + SnCI2→ Hg2CI2+ SnCI4
Removal of oxygen
CuO + H2 → H2o + Cu
Removal of electronegative radical
2FeCI3 + SnCI2→ 2FeCI2+ SnCI4
Redox Reactions in terms of Electron Transfer Reactions
According to electronic concept the processes which involve loss of electrons are called oxidation reactions. Similarly processes which involve gain of electrons are called reduction reactions.
The atom which reduced, act as oxidising agent and the atom which oxidised act as reducing agent.
Oxidising agent (Acceptor of electron)
The substance which can bring about .oxidation of other substances is called an oxidising agent. Thus an oxidising agent is the substance that provides oxygen or removes hydrogen from any other substance or accepts electrons.
eg. S + O2 → SO2 (O2 is oxidising agent)
H2S + Cl2 → 2HCI + S (Cl2 is oxidising agent)
6HNO3 + S → H2SO4 + 2H2O + 6NO2 (HNO3is oxidising agent)
Reducing agent (Donor of electron)
The substance which can bring about reduction of other substance is called reducing agent . Thus reducing agent is the substance that provides hydrogen or removes oxygen from any other substances or donates electrons.
eg. ZnO + C → Zn + CO (C is reducing agent)
FeO + CO → Fe + CO2(CO is reducing agent)
H2SO4 + 2HBr→ SO2 + Br2 + 2H2O(Br is reducing agent)
Competitive Electron Transfer Reactions
Direct redox reaction.
A reaction in which the reacting species which is capable of losing electrons (reducing agent) and that capable of gaining electrons (oxidising agent) are present in the same solution is termed as direct redox reaction.
Indirect redox reaction or Electro chemical cell reaction.
The reaction in which the reacting species which is capable of losing electrons (reducing agent) and that capable of gaining electrons (oxidising agents) are kept separately and the transfer of electrons from one species to another does not take place directly is called an indirect redox reaction.
Based upon the relative electron releasing tendencies, metals have been arranged in the form of a series as reactive series of metals
Oxidation number is the apparent charge which an atom of the compound or ion has.
What is the oxidation number of Mn in KMnO4.
Oxidation number of Mn in KMnO4.
1 + x + (-2) x 4 = 0 ⇒ x = + 7
The oxidation number is expressed by putting a Roman numeral representing the oxidation number in parenthesis after the symbol of the metal in the molecular formula.
Stanous chloride is written as Sn(ll)CI2.
Oxidation and Reduction in terms of Oxidation Number
An increase in the oxidation number of the element in the given substance.
A decrease in the oxidation number of the element in the given substance.
Oxidising agents or oxidants.
A reagent which can increase the oxidation number of an element in a given substance are called oxidants.
Reducing agents or reductants.
A reagent which lowers or decrease the oxidation number of an element in a given substance are called reductants.
HBr – oxidation (reducing agent)
Cl2– reduction (oxidising agent)
Types of Redox Reactions
1. Combination reactions.
The reaction involves combination of a compound from two or more components atleast one of which must be in the elemental form or both the components are in the elemental state.
2. Decomposition reactions.
The reaction involves decomposition of a compound into two or more components atleast one of which must be in the elemental state.
3. Displacement reactions.
In a displacement reaction, an ion or an atom in a compound is replaced by an ion or an atom of another element.
eg., A + BC→ AB + C
- Metal displacement reaction. A metal in a compound can be displaced by another metal in the uncombined state.
- Non-metal displacement reaction. This include hydrogen displacement and a rarely occuring reaction involving oxygen displacement.
4. Disproportionation reactions.
In a disproportionation reaction an element in one oxidation state is simultaneously oxidised and reduced.
Balancing of Redox Reactions
Oxidation Number Method
Step 1: Write the correct formula for each reactant and product.
Step 2: Indicate the oxidation number of each atom involved in the reaction. Identify the elements whose oxidation numbers are changed.
Step 3: Calculate the increase or decrease in oxidation numbers per atom. Multiply this number of increase of oxidation number with the number of atoms which are undergoing change.
Step 4: Equate the increase in oxidation number with decrease in oxidation number on the reactant side by multiplying the formulae of the oxidising and reducing agents.
Step 5: Balance the equation with respect to all other atoms except hydrogen and oxygen.
Step 6: Finally balance hydrogen and oxygen. For reactions taking place in acidic solution, add H+ ions to the other side deficient in hydrogen atoms. For reactions taking place in basic medium, add H20 molecules to the side deficient in hydrogen atoms and simultaneously acid equal number of OH– ions on the other side of the equation.
Half Reaction Method or Ion-Electron Method
In this method, the two half equations are balanced separately equation. Balancing of chemical equation by ion-electron method can be done through the following steps:
Step 1: Write down oxidation number of the element which appears in the given skeleton equation.
Step 2: Identify the species getting oxidised arid that getting reduced from the oxidation numbers of the elements which occur in them.
Step 3: Split the whole in two half equations.
Step 4: Balance both the half equations separately as follows:
i. Balance all atoms other than H and O.
ii. Add electrons to either side to balance the ionic charges.
iii. Balance H and O by suitably adding H+ or H2O on the side as required.
Step 5: Multiply one or both half equations with a suitably factor so that the electrons are balanced.
Step 6: Add the two balanced and matched half equations to get the balanced equation for the overall reaction.
Redox Reactions as the Basis for Titrations
The reaction in which oxidation and reduction take place simultaneously is called redox reaction. Volumetric titrations based on simultaneous oxidation and reduction reactions are termed as redox titrations. Redox system having higher (more positive or less negative) E° value will show greater tendency for reduction. In redox systems the titration method can be adopted to determine the strength of a reductant / oxidant using a redox sensitive indicator.
Redox Reactions and Electrode Potential
Redox couple. A redox couple is defined as that having together the oxidised and reduced forms of a substance taking part in an oxidation or reduction half reactions.
Electrode potential. The tendency of an electrode to lose electrons or get oxidised (oxidation potential) and to gain electrons or get reduced (reduction potential) when it is in contact with its own ion or electrolyte is called electrode potential.
Standard Electrode Potential.
The tendency of an electrode to lose electrons or gain electrons when it is in contact with its own electrolyte at standard condition (1 atmospheric pressure and at 298 K) is called standard electrode potential. By convention, the standard electrode potential (E°) of hydrogen electrode is zero.
Redox reactions in Daily Life
- The redox reactions find wide applications in the study of electrode processes and cells.
- In metallurgical process. Metal oxides are reduced to metals by using suitable reducing agents.
- In photosynthesis.
Here Co2 is reduced to carbohydrate arid water is oxidised to oxygen.
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