CBSE Class 12 Chemistry (Physical Chemistry)
Chapter 2: Electrochemistry
20 Important Questions and Answers
As per CBSE Syllabus 2026–27
1. What is electrochemistry? Explain its importance.
Answer:
Electrochemistry is the branch of chemistry that studies the relationship between electrical energy and chemical energy. It deals with chemical reactions involving the transfer of electrons, known as redox reactions. Electrochemistry is important because it helps in understanding the working of batteries, fuel cells, electroplating, corrosion, and industrial extraction of metals. It has numerous practical applications in everyday life, including power generation and storage. Electrochemical principles are also used in medical devices, sensors, and environmental monitoring. Thus, electrochemistry plays a vital role in both scientific research and technological development.
2. What is an electrochemical cell? Describe its components.
Answer:
An electrochemical cell is a device in which a chemical reaction produces electrical energy. It consists of two electrodes and an electrolyte solution. The electrode where oxidation occurs is called the anode, while the electrode where reduction occurs is called the cathode. The electrolyte allows the movement of ions between the electrodes. A salt bridge is often used to maintain electrical neutrality by permitting ion flow between the two half-cells. The flow of electrons from anode to cathode through an external circuit generates electric current. Electrochemical cells are widely used in batteries and power sources for electronic devices.
3. What is a Daniell cell? Explain its working.
Answer:
A Daniell cell is a galvanic cell that converts chemical energy into electrical energy through a spontaneous redox reaction. It consists of a zinc electrode dipped in zinc sulfate solution and a copper electrode dipped in copper sulfate solution. The two solutions are connected by a salt bridge. Zinc acts as the anode and undergoes oxidation, releasing electrons. Copper acts as the cathode where copper ions gain electrons and get reduced. Electrons flow from zinc to copper through the external circuit, producing electric current. The Daniell cell demonstrates the basic principles of electrochemical energy conversion.
4. Define electrode potential. What factors affect it?
Answer:
Electrode potential is the tendency of an electrode to gain or lose electrons when it is in contact with an electrolyte solution. It is measured relative to a standard reference electrode. Electrode potential depends on several factors, including the nature of the electrode, concentration of ions in solution, temperature, and pressure in case of gases. A higher reduction potential indicates a greater tendency to gain electrons. Electrode potentials help predict the direction of redox reactions and calculate cell voltages. They are essential in understanding the behavior and efficiency of electrochemical cells.
5. What is Standard Electrode Potential (E°)?
Answer:
Standard electrode potential (E°) is the electrode potential measured under standard conditions, which include 1 M concentration of ions, 1 atm pressure for gases, and a temperature of 298 K. It is measured with respect to the Standard Hydrogen Electrode (SHE), whose potential is assigned as zero volts. Standard electrode potentials indicate the relative tendency of species to undergo reduction. A more positive value signifies a stronger oxidizing agent, while a more negative value indicates a stronger reducing agent. These values are widely used for predicting reaction feasibility and calculating standard cell potentials.
6. What is a salt bridge? State its functions.
Answer:
A salt bridge is a U-shaped tube containing a concentrated solution of an inert electrolyte such as potassium chloride or potassium nitrate in a gel. It connects the two half-cells of an electrochemical cell. Its main function is to complete the electrical circuit by allowing ion migration. It maintains electrical neutrality by preventing the accumulation of positive and negative charges in the respective half-cells. The salt bridge also minimizes liquid junction potential and prevents direct mixing of the electrolytes. Without a salt bridge, the electrochemical cell would stop functioning due to charge buildup.
7. Why is the Standard Hydrogen Electrode (SHE) used as a reference electrode?
Answer:
The Standard Hydrogen Electrode (SHE) is used as a reference electrode because its potential is fixed at zero volts under standard conditions. It consists of a platinum electrode in contact with hydrogen gas at 1 atm pressure and hydrogen ion solution of 1 M concentration. Since absolute electrode potentials cannot be measured directly, the SHE serves as a standard against which all other electrode potentials are determined. It provides a reliable and reproducible reference point. Standard electrode potential values listed in electrochemical series are measured relative to the SHE.
8. What is EMF of a cell? How is it measured?
Answer:
The electromotive force (EMF) of a cell is the maximum potential difference between the two electrodes when no current flows through the circuit. It represents the driving force responsible for electron flow. EMF is measured using a potentiometer or a high-resistance voltmeter under open-circuit conditions. The EMF of a cell depends on the nature of the electrodes, electrolyte concentrations, and temperature. A positive EMF indicates a spontaneous cell reaction. The EMF provides information about the energy available from the electrochemical reaction and the efficiency of the cell.
9. State the Nernst equation and its significance.
Answer:
The Nernst equation relates the electrode potential of a cell to the concentration of reactants and products involved in the reaction. It is used when conditions differ from standard conditions.
E = E^\circ – \frac{0.0591}{n}\log Q
Here, E is the electrode potential, E° is the standard electrode potential, n is the number of electrons transferred, and Q is the reaction quotient. The equation helps calculate cell potentials under non-standard conditions. It is widely used to determine ion concentrations, equilibrium constants, and the direction of electrochemical reactions.
10. What is conductance? Differentiate between metallic and electrolytic conductance.
Answer:
Conductance is the ability of a substance to allow the flow of electric current. It is the reciprocal of resistance and is measured in siemens (S). Metallic conductance occurs due to the movement of free electrons in metals and decreases with increasing temperature. Electrolytic conductance occurs due to the movement of ions in solutions and generally increases with temperature. In metallic conductors, no chemical change takes place, whereas in electrolytic conductors, chemical reactions may occur at the electrodes. Both types of conductance are important in understanding electrical and electrochemical systems.
11. Define specific conductance and molar conductivity.
Answer:
Specific conductance, also called conductivity (κ), is the conductance of a solution contained between two electrodes one centimeter apart and having a cross-sectional area of one square centimeter. Molar conductivity (Λm) is the conductance of all ions produced by one mole of an electrolyte dissolved in a solution. It is expressed in S cm² mol⁻¹. Specific conductance depends on the number of ions present in a unit volume, whereas molar conductivity depends on dilution. Molar conductivity generally increases with dilution because ions move more freely and experience less interionic attraction.
12. How does molar conductivity vary with dilution?
Answer:
Molar conductivity increases with dilution because the ions become more separated and move more freely in solution. For strong electrolytes, the increase is relatively small since they are already almost completely ionized. For weak electrolytes, the increase is significant because dilution increases the degree of ionization, producing more ions. At infinite dilution, interionic interactions become negligible and molar conductivity reaches its maximum value. The variation of molar conductivity with dilution helps determine the dissociation behavior of electrolytes and provides valuable information about ionic mobility and electrolyte strength.
13. State Kohlrausch’s Law of Independent Migration of Ions.
Answer:
Kohlrausch’s Law states that at infinite dilution, each ion contributes independently to the total molar conductivity of an electrolyte, regardless of the nature of the other ion present. According to this law, the limiting molar conductivity of an electrolyte is equal to the sum of the individual ionic conductivities of its constituent ions. This law is useful for determining limiting molar conductivities of weak electrolytes, degree of dissociation, and solubility of sparingly soluble salts. It also provides evidence that ions migrate independently in very dilute solutions.
14. What is electrolysis? Give one application.
Answer:
Electrolysis is the process in which electrical energy is used to drive a non-spontaneous chemical reaction. It takes place in an electrolytic cell where an external power source forces electrons to move through the circuit. During electrolysis, oxidation occurs at the anode and reduction occurs at the cathode. Electrolysis is widely used in industries for metal extraction, purification, electroplating, and chemical manufacturing. One important application is the electrolytic refining of copper, where impure copper is purified to obtain high-purity copper required for electrical wiring and electronic equipment.
15. State Faraday’s First Law of Electrolysis.
Answer:
Faraday’s First Law of Electrolysis states that the mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. Mathematically, the mass deposited increases as more electric charge flows through the solution. This law shows that electrochemical changes depend on the amount of electricity supplied. It forms the basis for quantitative calculations in electrolysis and is widely applied in electroplating, metal extraction, and industrial electrochemical processes. The law was established through extensive experimental observations by Michael Faraday.
16. State Faraday’s Second Law of Electrolysis.
Answer:
Faraday’s Second Law of Electrolysis states that when the same quantity of electricity passes through different electrolytes, the masses of substances deposited are proportional to their equivalent masses. This means that substances with higher equivalent masses will be deposited in greater amounts for the same electric charge. The law establishes a relationship between chemical change and electrical charge. It is important in determining equivalent masses of elements and predicting the amount of material produced during electrolysis. Together with the first law, it forms the foundation of electrochemical calculations.
17. What is corrosion? Explain rusting of iron.
Answer:
Corrosion is the gradual deterioration of a metal due to chemical or electrochemical reactions with its environment. Rusting of iron is the most common example of corrosion. It occurs when iron reacts with oxygen and moisture present in the atmosphere. Iron undergoes oxidation to form iron ions, while oxygen is reduced in the presence of water. These products eventually form hydrated iron(III) oxide, commonly known as rust. Rust weakens the metal and reduces its durability. Corrosion can be prevented by painting, galvanization, alloying, and cathodic protection methods.
18. What are fuel cells? Mention their advantages.
Answer:
Fuel cells are electrochemical devices that convert the chemical energy of fuels directly into electrical energy through redox reactions. A common example is the hydrogen-oxygen fuel cell. In these cells, hydrogen acts as the fuel and oxygen acts as the oxidant. Fuel cells continuously generate electricity as long as reactants are supplied. Their advantages include high efficiency, low environmental pollution, continuous operation, and reduced dependence on conventional fuels. The hydrogen-oxygen fuel cell produces water as the only by-product, making it an environmentally friendly energy source for future applications.
19. What is cell notation? Write the notation for a Daniell cell.
Answer:
Cell notation is a symbolic representation of an electrochemical cell. It provides information about the electrodes, electrolytes, and direction of electron flow. In cell notation, the anode is written on the left and the cathode on the right. A single vertical line represents a phase boundary, while a double vertical line represents the salt bridge. For a Daniell cell, the notation is:
Zn | Zn²⁺ (1 M) || Cu²⁺ (1 M) | Cu
This notation indicates that zinc undergoes oxidation at the anode and copper ions undergo reduction at the cathode, producing electrical energy.
20. Explain the relationship between Gibbs free energy and EMF of a cell.
Answer:
The relationship between Gibbs free energy change (ΔG) and the EMF of a cell helps determine the spontaneity of electrochemical reactions.
\Delta G = -nFE
Here, ΔG is the Gibbs free energy change, n is the number of electrons transferred, F is Faraday’s constant, and E is the cell EMF. A positive EMF results in a negative ΔG, indicating a spontaneous reaction. Under standard conditions, the equation is written as ΔG° = –nFE°. This relationship connects thermodynamics with electrochemistry and helps evaluate the feasibility and energy changes of cell reactions.