Problem 31 - A Complete Resource Book in Chemistry for JEE Main

Question

In the electrolysis of a fused salt, the weight of the deposit on the electrode, will not depend on (a) current intensity (b) electrochemical equivalent of the ions (c) time for electrolysis (d) temperature of the bath

Step-by-Step Solution

Answer

(d) temperature of the bath

Step 1: Understanding the Electrolysis Process

Electrolysis involves using an electric current to cause a chemical change, typically decomposition. In a fused salt, ions move towards their respective electrodes to get deposited as solid materials.

Step 2: Factors Affecting Electrode Deposits

The amount of substance deposited at the electrode is influenced by Faraday's laws of electrolysis. According to these laws, the mass of the substance (m) deposited is proportional to the total electric charge (Q) and is represented as: \[ m = Z \cdot Q \] where \( Z \) is the electrochemical equivalent, and \( Q \) is the charge passed through the substance.

Step 3: Considering Current Intensity

The current intensity (I) affects the charge (Q) since:\[ Q = I \cdot t \]Therefore, the mass deposited (m) is indeed dependent on the current intensity.

Step 4: Role of Electrochemical Equivalent

The electrochemical equivalent \( Z \) defines the mass of substance deposited per unit charge and clearly influences the mass deposited during electrolysis.

Step 5: Influence of Time on Electrolysis

Time (t) is directly proportional to the charge since:\[ Q = I \cdot t \]As a result, the mass of the deposited substance depends on the duration of electrolysis.

Step 6: Effect of Temperature on the Bath

While temperature can affect the conduction properties and efficiency of the process, the fundamental physics presented in Faraday's law do not include temperature as a variable affecting the mass deposited. Temperature impacts are secondary and indirect through conductivity or ion mobility but not directly on mass.

Key Concepts

Electrochemical Equivalent

The electrochemical equivalent, abbreviated as \( Z \), plays a pivotal role in the phenomenon of electrolysis. This value determines the mass of an element or compound deposited or dissolved at an electrode for a given amount of electrical charge. It's a unique constant for each substance and signifies how much "reacting power" it has when subjected to an electric current.
Faraday's laws of electrolysis provide the relationship between the quantity of electricity and the mass of substance deposited. This relationship is mathematically expressed as \( m = Z \cdot Q \), where:

• \( m \) is the mass of the substance in grams.
• \( Z \) is the electrochemical equivalent in grams per coulomb.
• \( Q \) is the total electric charge in coulombs.

Understanding \( Z \) is crucial because it directly tells us how much of a particular material will be deposited on the electrode for a given charge. This means that for electrolysis processes, knowing the electrochemical equivalent helps predict the exact amount of material that can be retrieved through different operational settings.

Current Intensity

Current intensity, or simply the amount of electric current, significantly influences electrolysis. In the electrochemical process, it defines the rate at which electricity is flowing and directly affects the amount of material that can be deposited.
Mathematically, the relationship is defined by the formula \( Q = I \cdot t \), where:

• \( Q \) is the electric charge in coulombs.
• \( I \) represents current intensity, measured in amperes.
• \( t \) is the time during which the current flows, in seconds.

Increasing current intensity means more charged particles flow per second. This, in turn, increases the total charge passing through the system during electrolysis, potentially leading to more mass being deposited on the electrode. Therefore, experimenting with different levels of current can significantly alter the outcomes in electrolysis, provided other conditions remain constant.

Effects of Temperature on Electrolysis

Temperature plays an interesting role in electrolysis. Though not a direct factor in Faraday's laws that determine the mass of deposits, it has notable effects on the electrolysis process itself.
Here is how temperature can influence it:

• Ionic Conductivity: Higher temperatures generally increase the mobility of ions. This is because the added heat reduces resistance, allowing ions to move more freely which can influence conduction efficiency.
• Reaction Rates: Increasing temperature typically increases chemical reaction rates; thus, the electrolysis reactions might occur more swiftly as the temperature rises.
• Energy Consumption: A higher temperature can reduce the energy requirement for maintaining the electrolyte in a molten or liquid state, which can lower the overall energy consumption of the system.

While the temperature doesn't change the fundamental relationship between charge and deposited mass, it affects the process's efficiency and kinetics. By adjusting the temperature, engineers can optimize the conditions to achieve desired results in real-world applications.