NEET Chemistry Redox Reactions and Electrochemistry
Redox Reactions and Electrochemistry PDF Notes, Important Questions and Synopsis
SYNOPSIS
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Electrochemical cell |
Galvanic cell |
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This cell converts electrical energy to chemical energy. |
This cell converts chemical energy to electrical energy. |
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It requires a source of external energy. |
It is a source of energy. |
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It has a cathode as the negative electrode. |
It has a cathode as the positive electrode. |
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It has an anode as the positive electrode. |
It has an anode as the negative electrode. |
Electrode potential:
For any electrode → oxidation potential (OP) = −Reduction potential (RP)
Ecell = RP of the cathode – RP of the anode
Ecell = RP of the cathode + OP of the anode
E°cell is always a +ve quality and the anode will be an electrode of low RP.
- Greater the SRP value, greater will be the oxidising power.
- Concentration cell: A cell in which both electrodes are made of the same material.
For all concentration cells, E°cell = 0. - Electrolyte concentration cell:
Example: Zn(s) / Zn2+ (c1) || Zn2+(c2) / Zn(s)
Different types of electrodes:
- Metal–metal ion electrode
Example: M(s)/Mn+
Mn++ ne→M(s) - Gas–ion electrode
Pt/H2(Patm)/Hn+(XM) as a reduction electrode. - Oxidation –reduction electrode
Example: Pt/Fe2+ , Fe3+
As a reduction electrode: AgCl(s)+e → Ag((s) +Cl - Metal-metal insoluble salt electrode
Example: Ag/AgCl,Cl-
As a reduction Electode: AgCl(s) + e → Ag(s) +Cl-
- Electrolysis:
- Similarly, the anion which is a stronger reducing agent (low value of SRP) is liberated first at the anode.
Faraday’s law of electrolysis:
First law:
The mass of an atom or ion oxidised or reduced at either electrode (during electrolysis) is directly proportional to the quantity of electricity passed through the electrolyte.
Second law:
When the same quantity of electricity is passed through different electrolytes, the mass of substances deposited is proportional to their respective chemical equivalent or equivalent weight.
Conductance:
- Conductance is the property of a conductor which facilitates the flow of electricity through it.
- Specific conductors or conductivity: Conductance of a solution of definite dilution enclosed in a cell having two electrodes of unit area separated by 1 cm.
- Equivalent conductance: Conductance of all the ions produced by 1 gram equivalent of an electrolyte in a given solution.
- Molar conductance: Conductance of all the ions produced by ionisation of 1 g mole of an electrolyte when present in V mL of solution.
Kohlrausch’s law: Equivalent conductivity of an electrolyte at infinite dilution is equal to the sum of conductances of the anions and cations.
Ionic mobility: Distance travelled by the ion per second under the potential gradient of 1 volt per cm. Its unit is cm2S-1V-1.
Battery: A battery consists of two or more voltaic cells connected in series.
- Primary batteries:
- In primary batteries, the reaction occurs only once and cannot be reused again.
Examples:
Leclanché cell: A zinc container acts as the anode, and the cathode is a carbon (graphite) rod surrounded by powdered manganese dioxide and carbon.
Anode:
Cathode:
Mercury cell: It consists of zinc and mercury amalgam as the anode and a paste of HgO and carbon as the cathode.
- In primary batteries, the reaction occurs only once and cannot be reused again.
- Secondary batteries are portable voltaic cells which are rechargeable.
- The most important secondary cell is the lead storage battery commonly used in automobiles and invertors.
Anode:
Cathode:
Overall reaction:
Corrosion:
- In corrosion, a metal is oxidised by loss of electrons to oxygen and the formation of oxides.
- It is an electrochemical phenomenon.
- Corrosion of iron:
Oxidation:
Reduction:
- Atmospheric oxidation:
Videos
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- Same moles of which of the following species will require minimum amount of acidified KMnO4 for complete oxidation? (1) Ferrous ion (2) Sulphide ion (3) Oxalate ion (4) Sulphite ion Please solve it. Also is there any shortcut to solve this question fast.
- Please answer this
- Please answer this
- Please answer this
- Relation between oxidising agent and power And reducing agent and power
- ⭕Help me in this question....Thanks☺️
- Please answer
- Sir, please tell me if the balancing of this reaction is possible or not? It is not a redox reaction, and the question to balance this reaction, is wrong, right?
- Please answer
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