Question

Faraday's law of electrolysis fails when (a) temperature is increased (b) inert electrodes are used (c) a mixture of electrolytes is used (d) in none of these cases

Short answer

Faraday's law of electrolysis does not fail under the conditions of increased temperature, use of inert electrodes, or use of a mixture of electrolytes; it fails in none of these cases.

Step-by-step solution

Understanding Faraday's Law

Faraday's laws of electrolysis relate the amount of material altered at an electrode during electrolysis to the amount of electricity used. The laws state that the amount of chemical change is proportional to the amount of current passed and to the equivalent weight of the material being electrolyzed. These laws apply under a set of standard conditions, such as constant temperature and the use of inert electrodes.

Analyzing Option (a)

When the temperature is increased, the ionic conductivity can change, and the reaction kinetics at the electrodes can be affected. However, the fundamental relationship that Faraday's laws describe between charge passed and substance electrolyzed remains valid. Temperature changes might affect the efficiency or rate, but they do not cause Faraday's laws to fail.

Analyzing Option (b)

Inert electrodes, such as platinum or gold, do not participate in the chemical reactions during electrolysis. They serve as a medium for the transfer of electrons without undergoing any chemical change themselves. The use of inert electrodes does not have an impact on the validity of Faraday's laws since the laws are concerned with the substances that are electrolyzed, not with the electrode material.

Analyzing Option (c)

When a mixture of electrolytes is used, multiple reactions can occur at the electrodes, and different substances can be electrolyzed. However, as long as the total charge passed through the system is known, Faraday's laws still apply to the individual substances being electrolyzed. Therefore, the use of a mixture of electrolytes does not cause Faraday's laws to fail; it simply makes the application of the laws more complex.

Conclusion

Faraday's laws of electrolysis are not invalidated by any of the conditions described in options (a), (b), or (c). They are robust laws that hold under a variety of conditions, including those where the external factors such as temperature, electrode type, and composition of electrolyte are varied. Thus, the correct answer is that Faraday's law of electrolysis fails in none of these cases.

Key concepts

Electrolysis

Electrolysis is a fascinating chemical process in which electrical energy is used to drive a non-spontaneous chemical reaction. This technique is widely utilized for various applications, including electroplating, refining metals, and even the production of chlorine and sodium hydroxide through the electrolysis of saltwater. To put it simply, during electrolysis, an electric current flows through an ionic substance that is either molten or dissolved in a suitable solvent, resulting in chemical reactions at the electrodes and separation of materials.

A classic electrolysis setup involves two electrodes connected to a source of direct current. When the electrodes are immersed in the electrolyte and the current is switched on, positive ions, which are called cations, move towards the negative electrode—the cathode—where reduction takes place. Meanwhile, negative ions, or anions, move towards the positive electrode—the anode—where oxidation occurs. The substance that undergoes decomposition is the electrolyte, and its ions must be free to move in the solution for electrolysis to happen.

Understanding electrolysis is crucial for grasping the concept of Faraday's laws of electrolysis, which describe the quantitative aspects of this process.

Inert Electrodes

Inert electrodes play a pivotal role in the process of electrolysis, but they do so in a very unassuming way. These electrodes are made from materials that do not react with the electrolyte or the products of electrolysis. Examples of inert electrode materials include platinum and gold. As the name suggests, 'inert' means that they do not actively participate in the chemical reactions happening within the electrolytic cell.

Why are such electrodes used? The answer lies in their stability. Because they don't react or interfere with the electrolysis process, inert electrodes provide a consistent and reliable surface for the transfer of electrons. This is important for a controlled and predictable electrolysis reaction, ensuring that the only substances altered at the electrodes are those intended—typically the solute within the solution or the ionic liquid.

Moreover, the presence of inert electrodes does not mean Faraday's laws of electrolysis are no longer applicable; in fact, it's quite the opposite. These laws are still very much at work, dictating the amount of substance altered by a certain amount of electric current, regardless of the electrode's material.

Temperature Effect on Electrolysis

Temperature is a notable player in the field of chemistry, and it doesn’t stand on the sidelines in electrolysis either. Increasing the temperature generally increases the rate of chemical reactions, and in the case of electrolysis, it can enhance the ionic mobility within the electrolyte. This heightened mobility potentially allows for a greater and more efficient flow of current, meaning that more material can potentially be electrolyzed in less time. However, this doesn't mean Faraday's laws crumble under the heat.

Faraday's laws, which relate the amount of electrical charge used to the quantity of substance electrolyzed, remain steadfast because they are based on proportional relationships. Changes in temperature might affect the kinetics and efficiency of the process, but the foundational principle—that the quantity of material altered at an electrode is directly proportional to the amount of electricity used—inherits its robustness from the laws of conservation of charge and matter, remaining uncompromised under such thermal variations.

Electrolyte Mixtures

Navigating the electrolysis of mixtures of electrolytes can be compared to attending a crowded party—there's a lot going on and it's all about interactions. When multiple salts, acids, or bases dissolve in the same solution, they each break down into their respective ions, adding complexity to the electrolysis process. This could lead to a mixture of different reactions occurring at each electrode, depending on the electrode potentials required to reduce or oxidize the various ions present.

Despite the seemingly convoluted situation, Faraday's laws of electrolysis still hold true. The laws assert that the total mass of substances altered at an electrode is directly proportional to the total charge passed through the electrolyte. This means that even when multiple substances are being electrolyzed, we can apply Faraday's laws to each individual reaction—if we know the total charge and we understand the chemistry of the competing reactions.

So, when approaching electrolyte mixtures, Faraday's laws don't throw in the towel. They simply ask for a more analytical approach to discern how each substance is affected, often requiring calculations that respect the individual material's equivalent weight and the specific current or charge involved in its electrolysis.