CUET UG Chemistry Booster Test – 3 Basics of Electrochemistry

According to NCERT, the maximum useful electrical work obtainable from a galvanic cell is directly related to the Gibbs energy change of the cell reaction. The relationship is expressed as: where is the number of electrons transferred, is the Faraday constant and is the cell potential. For a spontaneous electrochemical reaction, the cell potential is positive and the Gibbs energy change is negative. A negative value of indicates that the reaction can perform useful work on the surroundings. The larger the negative value of Gibbs energy, the greater the maximum electrical work that can be obtained. Therefore, the decrease in Gibbs energy is the thermodynamic parameter that governs the electrical work output of a spontaneous galvanic cell. Hence option B is correct.

NCERT explains that conductivity depends on the number of ions present per unit volume. When an electrolyte solution is diluted, the number of ions per unit volume decreases, causing conductivity to decrease. However, molar conductivity increases because the ions experience less interionic attraction and move more freely. For strong electrolytes, a plot of molar conductivity against the square root of concentration can be extrapolated to zero concentration to obtain the limiting molar conductivity. Statement 4 is incorrect because dilution decreases rather than increases the number of ions per unit volume. Therefore statements 1, 2 and 3 are correct.

For the Daniell cell, the Nernst equation is As the reaction proceeds, zinc ions accumulate in solution while copper ions are consumed. Consequently, the reaction quotient increases. The logarithmic term therefore becomes larger, causing the cell potential to decrease progressively. Eventually, at equilibrium, the cell potential becomes zero and no further electrical work can be obtained. Therefore option C is correct.

Standard reduction potential measures the tendency of a species to gain electrons. A higher positive value indicates a stronger tendency to undergo reduction. Comparing the given values: The decreasing order is therefore: Hence option D is correct.

The Faraday constant is defined as the total electric charge carried by one mole of electrons. It is given by: where is Avogadro's number and is the electronic charge. Its value is approximately: Because it represents charge per mole, the correct SI unit is coulomb per mole. The Faraday constant plays a central role in electrochemistry and appears in relationships involving electrolysis, cell potentials and Gibbs energy calculations. Therefore option B is correct.

According to NCERT, Gibbs energy change is an extensive thermodynamic property. This means its value depends on the quantity of matter participating in the reaction. For the Daniell cell reaction, if the entire equation is multiplied by two, the standard Gibbs energy change also doubles. This behaviour is characteristic of extensive properties such as mass, volume and total energy. In contrast, quantities like temperature and pressure are intensive properties because they do not depend on the amount of substance present. Therefore, is an extensive thermodynamic property and option D is correct.

The standard electrode potential is the electrode potential measured under standard conditions, where the concentration of ionic species is unity, gases are at one bar pressure and the temperature is specified. Since absolute electrode potentials cannot be measured directly, NCERT defines standard electrode potentials relative to the Standard Hydrogen Electrode (SHE), whose potential is assigned zero volt. Standard electrode potentials provide a convenient method for comparing the tendencies of different species to undergo oxidation or reduction. These values are extensively used in predicting spontaneity, cell potential and oxidising or reducing strength. Therefore option C is correct.

During the discharge of a lead storage battery, the lead electrode acts as the anode. At this electrode, lead metal undergoes oxidation according to the reaction: Since lead loses electrons, it is oxidised. The substance that undergoes oxidation is called the reducing agent because it supplies electrons to another species. Meanwhile, lead dioxide at the cathode undergoes reduction. The lead storage battery is widely used in automobiles because it can deliver large currents and is rechargeable. Therefore solid lead acts as the reducing agent during discharge and option A is correct.

Kohlrausch's Law states that at infinite dilution, the molar conductivity of an electrolyte equals the sum of the ionic contributions of its constituent ions. Faraday's First Law of Electrolysis states that the amount of substance liberated during electrolysis is directly proportional to the quantity of electricity passed. The Nernst Equation relates cell potential to concentration through the reaction quotient. Faraday's Second Law states that when the same quantity of electricity passes through different electrolytes, the masses liberated are proportional to their equivalent weights. Therefore the correct matching is: 1-b, 2-c, 3-d, 4-a

NCERT explains that certain electrode reactions, particularly gas evolution reactions such as oxygen evolution, may require a voltage greater than that predicted by thermodynamics. Although the reaction is thermodynamically feasible, kinetic factors such as activation energy barriers and slow electron-transfer processes hinder the reaction rate. Consequently, an additional potential must be applied before the reaction proceeds at a measurable rate. This extra voltage is called overpotential or overvoltage. Overpotential plays an important role in industrial electrolysis because it affects energy consumption and electrode efficiency. Therefore option C is correct.

In electrolytic refining of copper, the impure copper slab is made the anode while a thin sheet of pure copper acts as the cathode. When electric current passes through the copper sulfate solution, copper atoms from the impure anode lose electrons and enter the solution as Cu²⁺ ions: Cu(s) → Cu²⁺ + 2e⁻ This process is oxidation. The Cu²⁺ ions then migrate through the electrolyte and are reduced at the cathode, depositing pure copper. Impurities either remain in solution or settle as anode mud. Thus, according to the passage, impure copper functions as the anode where dissolution occurs.

In the electrolytic refining of copper, Cu²⁺ ions present in the copper sulfate solution move toward the negatively charged cathode. At the cathode they gain electrons according to the reaction: Cu²⁺ + 2e⁻ → Cu(s) This process is reduction and results in the deposition of pure copper on the cathode surface. The discharged species is therefore the Cu²⁺ ion. Sulfate ions remain in solution and do not get discharged under these conditions.

Biological communication depends on electrochemical processes involving ion movement across cell membranes. Nerve impulses are generated by changes in membrane potential and transmitted through neurons to the brain and other parts of the body. Therefore biological signaling possesses an electrochemical origin and is transmitted through cells. It is not isolated from electrochemical laws; rather, it is governed by them. Furthermore, biological signaling is fundamentally different from the operation of industrial thermal power plants.

The electrochemical nature of nerve impulses demonstrates that the principles of physical chemistry are not restricted to laboratory systems or industrial electrolysis. They also explain fundamental biological processes such as neuronal communication, muscle contraction and ion transport across membranes. This broad applicability shows that electrochemistry is a highly interdisciplinary subject connecting chemistry, physics, biology and medicine. Hence the laws of physical chemistry govern many biological mechanisms.

An active electrochemical method of corrosion prevention involves attaching a more reactive metal such as magnesium or zinc to the iron structure. Because these metals have more negative electrode potentials, they oxidize preferentially: Zn → Zn²⁺ + 2e⁻ The electrons supplied prevent oxidation of iron, thereby protecting the structure from corrosion. This technique is known as cathodic protection using a sacrificial anode and is widely employed in pipelines, ship hulls and underground storage tanks. It represents a direct application of electrochemical principles to environmental and structural preservation.

The Hydrogen Economy is a proposed energy system in which hydrogen serves as a major fuel source. For hydrogen to remain environmentally sustainable, it should be produced using renewable energy resources. One of the most promising methods is the electrolysis of water powered by solar energy. During electrolysis, water decomposes into hydrogen and oxygen: 2H₂O(l) → 2H₂(g) + O₂(g) When solar energy supplies the required electrical energy, the entire process becomes renewable and nearly pollution-free. This approach reduces dependence on fossil fuels and minimizes greenhouse gas emissions, making it an important goal for future sustainable energy systems.

The lead storage battery is a secondary cell that can be recharged and reused. It contains approximately 38% sulfuric acid as the electrolyte. During discharge, both the lead anode and lead dioxide cathode are converted into lead sulfate (PbSO₄). When an external current is passed in the reverse direction, the discharge reactions are reversed and the original electrode materials are regenerated. Statement 1 is incorrect because PbO₂ forms the positive plate (cathode during discharge), whereas the anode consists of spongy lead (Pb). Therefore statements 2, 3 and 4 are correct.

Hydrogen-oxygen fuel cells employ porous electrodes coated with finely divided platinum or palladium. These noble metals function as catalysts that increase the rate of oxidation and reduction reactions occurring at the electrodes. The catalysts lower activation energy and allow efficient electron transfer without being consumed during operation. Their presence significantly improves fuel cell efficiency and performance. Therefore platinum and palladium are incorporated primarily as catalytic materials.

The Nernst equation relates cell potential to the concentrations of reactants and products participating in an electrochemical reaction. Since practical electrochemical systems seldom operate under standard conditions, the Nernst equation enables the calculation of cell potential at any concentration. It forms a crucial link between electrochemistry, thermodynamics and chemical equilibrium. This theoretical relationship greatly expands the scope of electrochemistry and allows prediction of cell behavior under real conditions.

The cell constant of a conductivity cell is defined as l/A, where l is the distance between electrodes and A is the electrode area. Since direct measurement is often inconvenient and inaccurate, the cell constant is determined experimentally. The cell is filled with a standard solution, usually potassium chloride (KCl), whose conductivity is accurately known. The resistance of the solution is measured and the cell constant is calculated using: Cell Constant = Conductivity × Resistance This method provides a precise value and is routinely used in conductometric measurements.