NEET Study Notes for Electrochemistry: The discipline in chemistry that deals with the study of the relationship between chemical reactions and electricity is called Electrochemistry. When, between a solid electrode or substance like an electrolyte, electrons flow, electric current triggers through electrolyte that causes liberation or absorption of heat, this is known as Electrochemical reactions.

• Electrochemistry forms part of Physical Chemistry in NEET Chemistry Syllabus. The overall weightage of this section is 32%. At least 1 question is expected from Electrochemistry.
• Candidates can practice sample questions after understanding the topics that are explained in this article as this will help you in scoring well for NEET 2022.

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Important topics in Electrochemistry

Electrochemical Cells

The device that helps in generation of chemical energy through chemical reactions is known as an electrochemical cell. A potential difference through chemical reactions is produced in electrodes due to electrochemical cells. The main components of electrochemical cells are- a pair of electron conductors, that are separated by an ionic conductor.

The two half cells in the electrochemical cell ensure that oxidation and reduction reaction takes place in each half of the cell.

Electrochemical cells consist of cathode and anode. The features of cathode and anode are:

Electrochemical Cells can be classified into

• Galvanic Cell- Galvanic cells are also known as Voltaic cells, In these cells transformation of chemical energy to electrical energy takes place. The occurrence of redox reactions in these cells is of spontaneous nature. While the anode in a Galvanic cell is negatively charged, the cathode is positively charged.
• Electrolytic Cell- In these cells, the transformation of electrical energy to chemical energy takes place. The occurrence of redox reactions requires energy which makes the non-spontaneous reactions. While the anode in an Electrolytic cell is positively charged while the cathode is negatively charged.

Check NEET Study Notes on Chemical Bonding

Electrode Potential

The contact of electrodes in a solution of its ions, leads to its tendency to lose or gain electrons. This is known as Electrode Potential. Electrode Potential is expressed in terms of volts and depending on its tendency to gain or lose electrons is called Oxidation or Reduction Potential.

Standard Electrode Potential

The measurement of potential for equilibrium is known as Standard Electrode Potential. It can also be defined as the standard value of EMF of a cell. The potential difference between electrolyte and electrode is the potential of an electrode, and this potential difference is called standard electrode potential.

We can determine the difference of two half-cells by

Eocell = Eored, Cathode – EoRed, Anode

Read:

• NEET Study Notes on Classification of Elements

• NEET Study Notes on Solid State

Electromagnetic Force of a cell (EMF)

Electrode Potential difference between two half cells is the Electromagnetic Force of a cell. It is also the reason for current flow in electrodes from high potential to low potential. The measuring force of free energy charge is also Electromagnetic Force.

Standard EMF of the cell can be determined by:

Specific Resistance, Specific Conductivity, and Molar Conductivity

Specific Resistance

The resistance offered on the application of a voltage of known amount in per unit length and cross-sectional area is called Specific Resistance.

where p is the specific resistance

R is resistance

A is the cross-sectional area

L is the length of the material

Specific Conductivity

The measure of a material’s ability to conduct electricity is known as Specific conductivity. The reciprocal of specific resistance, it is represented by K

where K is the conductivity

p is the resistivity

Thus, Specific Conductivity = Conductance * cell constant

S.I Unit of conductance is Siemens.

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Molar Conductivity

Conductivity of ions that are produced by dissolving a mole of electrolyte in a solution is called Molar Conductivity.

Molar Conductivity is given by

where K is the specific conductivity

V is the concentration in mole per liter

Variation of Molar Conductivity

With an increase in dilution and decrease in concentration, molar conductivity for strong and weak electrolytes increases.

• In the case of strong electrolytes, with an increase in concentration, molar conductivity also increases.
• In the case of weak electrolytes, with an increase in concentration, molar conductivity increases gradually.

Factors that affect Molar conductivity

• Nature of Electrolyte- In aqueous solutions, strong electrolytes are completely ionized. These have high specific conductivity. Examples- KCl, NH₄NO₃, HCl, weak electrolytes get ionized in fewer proportions. The conductivity is also less.
• Temperature- Inter ionic attraction, viscosity, and solvation of ion are decreased with an increase in temperature. This increase in temperature leads to an increase in conductivity.
• Viscosity- The higher the viscosity of solvent is, the less will be the conductivity.

Kohlrausch’s Law

As per Kolkrausch’s Law, at infinite dilution, the total of cations and anions ionic conductivities combine to the molar conductivity of an electrolyte.

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Nernst Equation

The relationship between ion concentration and electrode potential is given by Nernst Equation. The cell potential of electrochemical cells can be determined by Nernst Equation. Nernst Equation can be used for the determination of cell potential in an electrochemical cell at a specific temperature, reactant concentration, and temperature.

For Single Electrode Potential, Nernst Equation is

where Ecell is the cell potential

R is the universal gas constant

T - temperature

F- Faraday constant

N- number of electrons transferred in redox reaction

Relationship between Nernst Equation, Equilibrium Constant and Gibbs Energy change:

ΔG° = – nFE°cell

Commercial Cell

Commercial Cells can be classified into Primary and Secondary Cells. Primary cells cannot be used again or recharged. Electrode Reactions cannot be reversed by a source of energy that is external. Examples of Primary Cells are Dry Cells, Mercury cells. Secondary Cells can be recharged and used again. Examples of Secondary Cells are- Lead Storage Batteries and Nickel Cadmium Storage Cell.

• Dry Cells- Dry Cells are also known as Leclanche cells. In a dry cell, a metal container of zinc is present. A low moistured paste of electrolyte covers the metal electrolyte. The zinc container base acts as an anode and the carbon rod acts as a cathode. Manganese Dioxide and ammonium chloride paste, surround these and produce a voltage of 1.5V maximum. These are irreversible.

Cathode Reaction- MnO₂ + + e– MnO(OH) + NH₃

Anode Reaction- 

Potential of Cell- 1.25 V to maximum 1.5 V

Read NEET Study Notes on Structure of Atom

Corrosion

When undesirable compounds like oxides, sulfides, carbonates are formed on the surface of metal gradually, over time due to reacting with moisture and gases in the atmosphere, it leads to corrosion.

Factors Affecting Corrosion

• Reaction with atmospheric gases like CO₂, SO₂ etc
• Contact with Impurities
• Increase in Temperature
• Exposure to Moisture

Read NEET Study Notes for Reaction Mechanism

Mechanism of Corrosion

Formation of rust on the iron surface occurs through;

• Pure Iron acts as the Anode whereas the Cathode is the Impure Surface.
• Electrolyte Reaction takes place

  

  

• Anode Reaction that takes place is : 
• Cathode Reaction that takes place is : 
• The net reaction that occurs on the surface is : 

Prevention of Corrosion

Corrosion can be prevented by the following steps:

• Painting, coating, electroplating, galvanization.
• Using Anti Rust Compounds
• Usage of means of electrical Protection

Faraday’s Law of Electrolysis

Faraday’s First Law of Electrolysis

The quantity of electricity that passes through an electrolyte is directly proportional to the quantity of the substance that deposits at an electrolyte.

    

where I is the current strength in ampere

T is time in seconds

Q is the quantity of charge in coulombs

Z- Electrochemical equivalent constant

Thus W= Z when I is 1 ampere, time is 1 second and Q is 1 coulomb

Electrochemical equivalent is the quantity of substance deposited by 1-ampere current that passes for 1 second.

Faraday’s Second Law

When electricity in the same amount passes through different electrolytes substances liberated at electrodes is proportional to chemical equivalent weights. Thus

   

Read:

NEET Study Notes on Carbonyl Compounds

NEET Study Notes on IUPAC and Isomerism

What is Faraday’s Constant?

Faraday’s Constant or one Faraday the amount of charge carried by one mole of electrons.

    

Electrodes

Substance that conducts electricity and helps in the connection of circuit’s non-metallic components is called Electrode. An electrode is mainly used for conducting electricity for alteration of current in different ways by coming in contact with non-metallic parts of the circuit.

The two main types of electrodes are:

• Inert- Inert electrodes do not participate in any reaction. The common inert electrodes are Platinum, Graphite, Gold, Rhodium.
• Reactive- Reactive electrodes dissolve into electrolytes and take part in reactions. Some of the common Reactive electrodes are lead, zinc, copper, and silver.

NEET Sample Questions on Electrochemistry

Question: In the process of electrolysis, when the same quantity of electricity passes through different electrolytes, what is a mass of substances proportional to?

1. Chemical Equivalents
2. Molecular weight
3. Molecular numbers
4. Valencies

Answer: Chemical equivalents

Question: What is prevented when petroleum jelly is applied to lead-acid battery terminals?

1. Local heating
2. Short-circuiting
3. Corrosion
4. All of these

Answer: Corrosion

Question: What will be applied with an iron, for good quality in the process of plating iron particles with Nickel?

1. Copper
2. Aluminum
3. Chromium
4. Silver

Answer: copper

Question: Purity of metal on extraction from ores can be removed. What is this process called?

1. Anodizing
2. Electroplating
3. Electrodeposition
4. Refining

Answer: Refining

Question: Which compounds aqueous solution is the best conductor of electric current?

1. Fructose
2. Hydrochloric Acid
3. Ammonia
4. Acetic Acid

Answer: Hydrochloric Acid

Question: Which device transforms energy of the combustion field of Hydrogen and methane into electrical energy?

1. Fuel Cell
2. Dynamo
3. Electrolytic Cell
4. Ni-Cd cell

Answer: Fuel Cell

Question: Which product is obtained at the anode when electrolysis occurs of dilute sulphuric acid with the usage of platinum electrodes

1. Hydrogen Sulphide
2. Hydrogen
3. Oxygen
4. Sulfur dioxide

Answer: Oxygen

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