Battery Combustion Rusting Refining of Impure metal Examples of Redox Reaction
Learning Objectives Classical and electronic concept of Oxidation and Reduction Oxidation number 11C08.1 Introduction to Redox Reaction
11C08.1 CV 1 Classical and Electronic Concept of Oxidation and Reduction
Redox = Red uction + Ox idation T he reaction in which oxidation and reduction reactions occur simultaneously . Redox Reaction
Oxidation Addition of oxygen/electronegative element to a substance Removal of hydrogen/electropositive element from a substance Classical Concept
Addition of hydrogen/electropositive element to a substance Removal of oxygen/electronegative element from a substance Reduction Classical Concept
Transfer of electron Electronic Concept
Transfer of electron Loss of electron Electronic Concept
Oxidation Increase in positive charge Decrease in negative charge Loss of electron Electronic Concept
Decrease in positive charge Increase in negative charge Reduction Gain of electron Electronic Concept
Example- Electronic Concept
Intensity of blue colour is reduced Initial stage Intermediate stage Final stage Cu +2 deposited as Cu Zn rod Electron Transfer Reactions
Intensity of blue colour is reduced Initial stage Intermediate stage Final stage Cu +2 deposited as Cu R elease of 2e - G ain of 2e - Zn rod E lectron releasing tendency of the metals : Zn > Cu Electron Transfer Reactions
Blue colour starts developing Initial stage Intermediate stage Final stage Ag deposited Cu rod Intensity of blue colour increases Electron Transfer Reactions
Blue colour starts developing Initial stage Intermediate stage Final stage Ag deposited Cu rod E lectron releasing tendency of the metals : Cu > Ag R elease of 2e - G ain of 2e - Intensity of blue colour increases Electron Transfer Reactions
Oxidation Reduction Addition of oxygen/electronegative element to a substance Removal of hydrogen/electropositive element from a substance Removal of oxygen/electronegative element from a substance Addition of hydrogen/electropositive element to a substance Loss of electron Gain of electron
11C08.1 CV 2 Oxidation Number
R eal or imaginary charge on an atom in the compound . . . . High E.N. -1 + 1 Oxidation Number (O.N.)
In elements, in the free or the uncombined state , each atom bears an oxidation number of zero . . . . . . . . . . Rules for Calculating Oxidation Number . .
For ions composed of only one atom; O.N. = charge on the ion. +2 +1 - 1 O.N.= +1 O.N.= +2 O.N.= -1 O.N. of Alkali metal in their compounds= +1 O.N. of Alkaline earth metal in their compounds = + 2 O.N. of Aluminum in its all compounds = +3 NOTE: Rules for Calculating Oxidation Number
3. O.N. of oxygen : In peroxide In super peroxide O.N.= -2 O.N.= -1 +1 +1 +1 -1 -1 +1 - 1 - 1 . . . . . . . . . . Mostly = Rules for Calculating Oxidation Number
In O.N.= +1 O.N.= +2 In -1 +1 -1 -1 +1 -1 +1 . . +1 . . . . . . . . Rules for Calculating Oxidation Number
O.N. of Hydrogen : O.N.= +1 Exception- When H is bound to metal, O.N. = -1 e.g. - LiH , NaH , CaH 2 +1 -1 -1 + 1 O.N.= -1 . . . . Mostly +1 Rules for Calculating Oxidation Number
5. O.N. = -1, halide ion Cl, Br and I when combine with oxygen ( oxoacid and oxoanion ) P ositive oxidation number For , For O.N=+7 O.N=+7 Rules for Calculating Oxidation Number
For a comound : Algebraic sum of O.N. of all the atoms = 0 For polyatomic ion : A lgebraic sum of O.N. of atoms = Charge on the ion . Rules for Calculating Oxidation Number
Metallic element Positive O.N. Non Metallic element Negative O.N. Transition metal Several positive O.N. Group 1 2 13 14 15 16 17 Element Na Mg Al Si P S Cl Compound NaCl MgSO 4 AlF 3 SiCl 4 P 4 O 10 SF 6 HClO 4 Highest O.N. state of the group element +1 +2 +3 +4 +5 +6 +7 OXIDATION NUMBER Rules for Calculating Oxidation Number
Alfred Stock Example :– Stannous chloride : Sn(II)Cl 2 S tannic chloride : Sn(IV)Cl 4 Stock Notation
Oxidation - O.N. of the element in the given substance Reduction - O.N. of the element in the given substance Reducing agent (R.A.)/Reductants : A reagent which can O.N. of the element in the substance Oxidizing agent (O.A.)/Oxidants : A reagent which can O.N. of the element in the substance Redox reaction - Reactions which involve change in O.N.
+1 - 2 +1 - 2 +4 - 2 Reduction Oxidation Example-
Oxidation Reduction Addition of oxygen/electronegative element to a substance Removal of hydrogen/electropositive element from a substance Removal of oxygen/electronegative element from a substance Addition of hydrogen/electropositive element to a substance Loss of electron Gain of electron O.N . of the element in the given substance O.N . of the element in the given substance
11C08.1 PSV 1
Q. Sol. Oxidation +3 +7 +2 +4 Reduction In this reaction act as a reductant so ans is (A)
ConcepTest Ready for a Challenge
Pause the video Time duration : 1 minute Q. What is the O.N. of Cl atom in and ?
O.N=+7 . . . . -2 + 2 . . . . + 2 -2 + 2 . . -2 . . +1 -1 . . O.N=+7 . . + 1 -1 . . . . -2 + 2 . . . . + 2 -2 . . . . + 2 -2 . . + 1 -1 Sol. Q. What is the O.N. of Cl atom in and ?
Summary Redox Reaction - The reaction in which oxidation and reduction reactions occur simultaneously. Oxidation Number(O.N.)- It represents the real or imaginary charge on an atom or element in the compound Oxidation Reduction Addition of oxygen/electronegative element to a substance Removal of oxygen/electronegative element from a substance Removal of hydrogen/electropositive element from a substance Addition of hydrogen/electropositive element to a substance Loss of electron Gain of electron O.N. of the element in the given substance O.N. of the element in the given substance
Learning Objectives Combination and Decomposition Reaction Displacement Reaction Disproportionation Reaction 11C08 .2 Types of Redox Reactions
11C08.2 CV 1 Combination and Decomposition Reaction
Combination reaction may be denoted as: Either one must be in elemental form Combustion Reactions + Combination Reaction
Combination reaction may be denoted as: Either one must be in elemental form Combustion Reactions Which make use of elemental dioxygen, are redox reaction + Combination Reaction
Combination reaction may be denoted as: Either one must be in elemental form Combustion Reactions Which make use of elemental dioxygen, are redox reaction Other Reactions + Combination Reaction
Opposite of combination reactions Breakdown of a compound into two or more components One of them must be in elemental state Decomposition Reaction
All decomposition reactions are not redox reaction No change in O.N. Decomposition Reaction
All decomposition reactions are not redox reaction No change in O.N. Decomposition Reaction
11C08.2 CV 2 Displacement Reaction
A n ion (or an atom) in a compound is replaced by an ion (or an atom) of another element Two types Metal displacement Non-metal displacement + + Replaces Displacement Reactions
A metal in a compound can be displayed by another metal in the uncombined state Finds application in purification of metals Metal Displacement
A metal in a compound can be displayed by another metal in the uncombined state Finds application in purification of metals Reduced Metal Displacement
A metal in a compound can be displayed by another metal in the uncombined state Finds application in purification of metals Oxidised Metal Displacement
A metal in a compound can be displayed by another metal in the uncombined state Finds application in purification of metals Reduced Metal Displacement
A metal in a compound can be displayed by another metal in the uncombined state Finds application in purification of metals Oxidised Metal Displacement
Zn > Cu > Ag Metal activity series
It includes hydrogen displacement and a rarely occurring reaction involving oxygen displacement Water Sodium Fire Non-metal Displacement
It includes hydrogen displacement and a rarely occurring reaction involving oxygen displacement Water Sodium Fire Non-metal Displacement
It includes hydrogen displacement and a rarely occurring reaction involving oxygen displacement All alkali metals and some alkaline earth metals and will displace hydrogen from cold water Water Sodium Fire Non-metal Displacement
Less active metals such as and react with steam to produce gas Production of dihydrogen gas Non-metal Displacement
Many metals are capable of displacing hydrogen from acids Used to prepare g as in the laboratory Metals Acids Dihydrogen gas Salt + + Non-metal Displacement
Note- and do not react with steam but are capable of displacing hydrogen from acids Non-metal Displacement
9 F 17 Cl 35 Br 53 I Halogens OXIDISING POWER Displacement reactions of Cl, Br and I using fluorine are not carried out in aqueous solution Halogen Activity Series
Chlorine can displace bromide and Iodide ions in an aqueous solution F or identifying and Gives colour Layer Test Halogen Activity Series
Bromine can displace Iodide ion in solution Halogen displacement reaction have industrial application Halides Halogen Oxidation Process Recovery strongest oxidising agent oxidise electrolytically Fluorine cannot recover from this method Halogen Activity Series
11C08.2 CV 3 Disproportionation Reaction
A n element is simultaneously oxidised and reduced One of the reacting elements should exist in atleast three oxidation state Disproportionation Reaction
P, S and Cl undergo disproportionation in alkaline medium : Disproportionation Reaction
P, S and Cl undergo disproportionation in alkaline medium : Disproportionation Reaction
Oxidises colour bearing stains of the substance to colourless compounds P, S and Cl undergo disproportionation in alkaline medium : Disproportionation Reaction
Fluorine reacts with alkali as: Being most E.N. element, it cannot exhibit any positive oxidation state F does not exhibit disproportionation tendency Exception of Disproportionation Reaction
ConcepTest Ready for a Challenge
Q . Pause the video Time duration: 2 minute Identify Disproportionation Reaction
Summary All combustion reactions, which make use of elemental dioxygen, as well as other reactions involving elements other than dioxygen, are redox reaction Decomposition reaction leads to the breakdown of a compound into two or more components In a disproportionation reaction an element in one oxidation state is simultaneously oxidised and reduced In a displacement reaction, an ion (or an atom) in a compound is replaced by an ion (or atom) of another element
Reference Questions NCERT Exercises : 8.4, 8.15, 8.24 and 8.28 NCERT In text : 5, 6 and 7 Workbook Questions : 5 and 19 11C08 .2 Types of Redox Reactions
11C08 .3 Balancing of Redox Reaction
Learning Objectives Oxidation number method Half reaction method 11C08 .3 Balancing of Redox Reaction
11C08.3 CV 1 Oxidation number method
Lets take an example of unbalanced equation in acidic medium Step 1 : Assign the oxidation number to all elements in the reaction. +6 - 2 +4 - 2 +3 +6 -2 Oxidation Number Method
Lets take an example of unbalanced equation in acidic medium Step 1 : Assign the oxidation number to all elements in the reaction. +6 - 2 +4 - 2 +3 +6 -2 Oxidation Number Method
+6 - 2 +4 - 2 +3 +6 -2 Step 3: Find the total change in O.N. for entire molecule. For , -3x2 = -6 For , +2x1 = +2 Oxidation Number Method Step 2: Balance atoms undergoing change in O.N.
Step 5: Charge balance using H + (acids) , OH - (basic) Step 4: Balance the or O.N. by multiplying some suitable number Oxidation Number Method +6 - 2 +4 - 2 +3 +6 -2
Step 6: Add H 2 O to balance H & O atom Step7: Verification: Oxidation Number Method Atoms of each element Total Charge
Q. Balance this equation by oxidation method in basic medium Sol. +7 -1 +4 +5 Step 1 : Assign the oxidation number to all elements in the reaction.
Q. Balance this equation by oxidation method in basic medium Sol. +7 -1 +4 +5 Step 1 : Assign the oxidation number to all elements in the reaction.
+7 -1 +4 +5 Step 2: Balance atoms undergoing change in O.N. Step 3: Find the total change in O.N. for entire molecule. For , -3x1 = -3 For , +6x1 = +6
Step 4: Balance the or O.N. by multiplying some suitable number +7 -1 +4 +5
Step 5: Charge balance using OH - (basic) Step 4: Balance the or O.N. by multiplying some suitable number +7 -1 +4 +5
Step 6: Add H 2 O to balance H & O atom Atoms of each element Total Charge Step7: Verification:
11C08 .3 PSV 1
Q. Balance the following equation in basic medium by oxidation number method. Sol . - 1 +5 -2 +2 Step 1 : Assign the oxidation number to all elements in the reaction.
Q. Balance the following equation in basic medium by oxidation number method. Sol . - 1 +5 -2 +2 Step 1 : Assign the oxidation number to all elements in the reaction.
Step 2: Balance atoms undergoing change in O.N. -2 Step 3: Find the total change in O.N. for entire molecule. For , +4x2 = +8 For , -6x1 = -6 - 1 +5 +2
Step 4: Balance the or O.N. by multiplying some suitable number - 1 +5 -2 +2
Step 4: Balance the or O.N. by multiplying some suitable number +5 -2 - 1 +2
Step 4: Balance the or O.N. by multiplying some suitable number +5 -2 - 1 +2
Step 4: Balance the or O.N. by multiplying some suitable number - 1 +5 -2 +2
Step 4: Balance the or O.N. by multiplying some suitable number Step 5: Charge balance using OH - (basic) Charge is already balanced - 1 +5 -2 +2
Step 6: Add H 2 O to balance H & O atom Atoms of each element Total Charge Step7: Verification:
11C08.3 CV 2 Half reaction Method
Lets take an example Step-1 Separate the equation into half – reactions Oxidation half reaction: +3 + 2 + 6 +3 I on-electron method Half Reaction Method
Lets take an example Step-1 Separate the equation into half – reactions Oxidation half reaction: Reduction half reaction: I on-electron method Half Reaction Method +3 + 2 + 6 +3
Half Reaction Method +3 + 2 + 6 +3 Oxidation half reaction Reduction half reaction Step-2 Balance the atom other than O and H in each half reaction individually. (Fe is already balanced)
Half Reaction Method +3 + 2 + 6 +3 Oxidation half reaction Reduction half reaction Step-3 For acidic medium, add H 2 O to balance O atoms and H + to balance H atoms
Half Reaction Method +3 + 2 + 6 +3 Oxidation half reaction Reduction half reaction Step-4 Add e - to one side of the half reaction to balance the charge
Half Reaction Method +3 + 2 + 6 +3 Oxidation half reaction Reduction half reaction Step-5 Multiply with suitable number to equalize e - in both half reaction
Half Reaction Method +3 + 2 + 6 +3 Oxidation half reaction Reduction half reaction Step-6 : Now add the two half reactions and cancel the e - on each side.
Half Reaction Method +3 + 2 + 6 +3 Step-7 Verification: Atoms of each element Total Charge Note- For reaction in basic medium. Firstly, follow all the steps of acidic medium . For each H + ion , add equal no. of OH - ion to both sides of the equation .
Q. Balance the following redox reaction in basic medium by ion-electron method. Sol . +7 +4 -1 Oxidation half reaction: Step-1 Separate the equation into half – reactions
+7 +4 -1 Q. Balance the following redox reaction in basic medium by ion-electron method. Sol . Oxidation half reaction: Reduction half reaction: Step-1 Separate the equation into half – reactions
Step-2 Balance the atom other than O and H in each half reaction individually. Oxidation half reaction Reduction half reaction
Step-2 Balance the atom other than O and H in each half reaction individually. Oxidation half reaction Reduction half reaction ( Mn is already balanced)
Oxidation half reaction Reduction half reaction Step-3 A dd H 2 O to balance O atoms and H + to balance H atoms
Oxidation half reaction Reduction half reaction Step-3 A dd H 2 O to balance O atoms and H + to balance H atoms
Oxidation half reaction Reduction half reaction Step-3 A dd H 2 O to balance O atoms and H + to balance H atoms
Oxidation half reaction Reduction half reaction Step-4 Add e - to one side of the half reaction to balance the charge
Oxidation half reaction Reduction half reaction Step-4 Add e - to one side of the half reaction to balance the charge
Oxidation half reaction Reduction half reaction Step-5 Multiply with suitable number to equalize e - in both half reaction
Oxidation half reaction Reduction half reaction Step-6 : Now add the two half reactions and cancel the e - on each side.
Step-7 In basic medium, For each H + ion , add equal no. of OH - ion to both sides of the equation
Step-8 Verification: Atoms of each element Total Charge
ConcepTest Ready for a Challenge
Q. Balance the following redox reaction in acidic medium by ion-electron method. Pause the video Time duration: 2 minute
Q. Balance the following redox reaction in acidic medium by ion-electron method. Sol . Step-1 Separate the equation into half – reactions Oxidation half reaction: +7 +4 +2 +6
Q. Balance the following redox reaction in acidic medium by ion-electron method. Sol . Step-1 Separate the equation into half – reactions Oxidation half reaction: Reduction half reaction: +7 +4 +2 +6
Step-2 Balance the atom other than O and H in each half reaction individually. Oxidation half reaction Reduction half reaction ( Mn is already balanced) ( S is already balanced)
Oxidation half reaction Reduction half reaction Step-3 A dd H 2 O to balance O atoms and H + to balance H atoms
Oxidation half reaction Reduction half reaction Step-3 A dd H 2 O to balance O atoms and H + to balance H atoms
Oxidation half reaction Reduction half reaction Step-4 Add e - to one side of the half reaction to balance the charge
Oxidation half reaction Reduction half reaction Step-4 Add e - to one side of the half reaction to balance the charge
Oxidation half reaction Reduction half reaction Step-5 Multiply with suitable number to equalize e - in both half reaction
Oxidation half reaction Reduction half reaction Step-5 Multiply with suitable number to equalize e - in both half reaction
Oxidation half reaction Reduction half reaction Step-6 : Now add the two half reactions and cancel the e - on each side.
Step-7 Verification: Atoms of each element Total Charge
Reference Questions NCERT Exercises : 8.18, 8.19, 8.23, and 8.25 NCERT In text : 8, 9 and 10 Workbook Questions : 17 and 18 11C08 .3 Balancing of Redox Reaction
11C08.4 Applications of Redox Reactions
11C08.4 Applications of Redox Reactions Learning Objectives Redox Reactions as the basis for Titrations Electrochemical cell Electrode Potential
11C08.4 CV 1 Redox Reaction as the basis for Titrations
Redox Reaction as the basis of Titration Redox Titrations Oxidant Reductant Indicator Method to determine the strength of a reductant/oxidant using a redox sensitive indicator Substance that changes color in response to a chemical change
Oxidizing Agents used in Redox Titration Potassium Permanganate Potassium Dichromate Iodine
Potassium Permanganate (oxidant) Self indicator Reductant End Point Pink colour
Potassium Dichromate (oxidant) Not a self indicator Reductant Diphenylamine / Diphenylbenzidine Intense blue colour End Point
Iodine KI solution Oxidising Agent / Iodine gives an intense blue colour with starch Starch
Iodine solution Sodium T hiosulphate Starch End Point
11C08.4 CV 2 Electrochemical Cell
Electrochemical Cell Devices which are used to convert electrical energy into chemical energy and vice versa Electrical energy is used to carry out a non-spontaneous redox reaction. Chemical energy of a spontaneous redox reaction is converted into electrical energy. Battery Anode Cathode Salt Solution Cathode Anode Salt Bridge
Galvanic Cell LOAN Left Oxidation Anode Negative Zn Anode Cu Cathode Overall cell reaction Solution Solution Voltmeter Anode Cathode Salt Bridge NaCl ( aq )
Salt Bridge U-shaped tube containing a chemically inert salt like Mobility of cation = Mobility of anion Completes the electrical circuit. Maintains the electrical neutrality of both electrodes. Maintains the spontaneity of cell reaction. Salt Bridge
IUPAC representation of Galvanic Cell At anode i.e. oxidation half: IUPAC notation: At cathode i.e. reduction half: IUPAC notation: Overall cell reaction: IUPAC notation: Zn Anode Cu Cathode Voltmeter Salt Bridge Galvanic Cell
11C08.4 CV 3 Electrode Potential
Electrode Potential Potential difference developed between electrode and electrolyte. Anode: Solution potential < Metal potential Cathode: Solution potential > Metal potential According to IUPAC convention, standard reduction potentials are now called standard electrode potentials . Electrode Potential Electromotive Force
Standard Hydrogen Electrode solution rod surface STP: and
Determination of standard electrode potential of metals solution rod Standard metal electrode Metal rod
Electrochemical Series Elements Electrode Reaction Elements Electrode Reaction (SHE) Oxidising Nature Reducing Nature
Selection of oxidising and reducing agents Higher the Reduction Potential higher will be the tendency to get reduced and better oxidising agent, So silver will undergo reduction. Lower the Reduction Potential higher will be the tendency to get oxidised and better reducing agent, So chromium will undergo oxidation. (SHE)
Reactivity of Metal Lower the Reduction Potential (more negative) higher will be the reactivity of metal , So chromium more reactive metal. (SHE)
11C08.4 PSV 1
Q. Given the standard electrode potentials, Arrange these metals in their increasing order of oxidising power. Sol. We know that, Higher the electrode potential, higher will the oxidising power of metal. So the order will be,
Summary Redox titrations Oxidizing agents: , , Electrochemical Cell (Galvanic cell) Salt bridge Electrode Potential- Potential difference developed between electrode and electrolyte Higher the Reduction Potential higher will be the tendency to get reduced and better oxidising agent
11C08.4 Applications of Redox Reactions Reference Questions NCERT Exercises: 26 to 30 Workbook Questions : 6 to 10, 14, 15, 20