Question

During the electrolytic reduction of alumina, the reaction at cathode is \(\ldots \ldots\) (a) \(3 \mathrm{~F}^{*} \rightarrow 3 \mathrm{~F}+3 \mathrm{e}^{-}\) (b) \(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}\) (c) \(2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{O}_{2}+\overline{4} \mathrm{H}^{+}+4 \mathrm{e}^{-}\) (d) \(\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al}\)

Short answer

(d) \( \mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al} \)

Step-by-step solution

Identify the Electrolytic Reaction

In the electrolytic reduction process, the cathode reaction involves the reduction (gain of electrons) of a substance. We need to find the correct reaction representing this process in the cathode for alumina.

Evaluate Each Option

Analyzing each option involves identifying which one represents reduction at the cathode: - (a) is not a cathode reaction because it shows oxidation (loss of electrons), not reduction. - (b) shows hydrogen ions gaining electrons to form hydrogen gas, but this is not typically involved in aluminum reduction. - (c) involves the formation of oxygen and hydrogen ions from water, which again denotes an anodic rather than cathodic reaction. - (d) shows aluminum ions gaining electrons to form aluminum, which is the correct reduction reaction for the cathode in the electrolytic reduction of alumina.

Select the Correct Reaction

From the analysis, option (d): \( \mathrm{Al}^{3+}+3 \mathrm{e}^{-} \rightarrow \mathrm{Al} \) is the correct reaction that represents the reduction process occurring at the cathode during the electrolytic reduction of alumina.

Key concepts

Cathode Reaction

The cathode reaction is a fundamental process in electrolysis, where reduction occurs. In this context, reduction means gaining electrons. During the electrolytic reduction of alumina, the cathode is the electrode where aluminum ions receive electrons. This process is essential for converting alumina (Aluminum oxide) into pure aluminum. The reaction occurring at the cathode can be represented by the equation:\(\mathrm{Al}^{3+}+3\mathrm{e}^{-}\rightarrow\mathrm{Al}\)Understanding this equation is crucial as it shows one aluminum ion gaining three electrons to transform into aluminum metal. This transformation is what makes the process economically viable, enabling the extraction of aluminum in its metallic form. The cathode reaction is vital because it defines the success of aluminum production in the electrolysis of alumina.

Reduction Reaction

In chemistry, a reduction reaction involves the gain of electrons by an atom or molecule. It is an integral part of redox (reduction-oxidation) reactions. In the electrolytic reduction of alumina, the role of the reduction reaction is to convert aluminum ions in the solution into solid aluminum. This occurs at the cathode - the negative electrode. The process can be summarized by these simple ideas:

• Aluminum ions ( Al^{3+} ) are positively charged.
• Electrons carry a negative charge.
• At the cathode, aluminum ions gain electrons, reducing their charge and forming aluminum metal.

The efficiency of a reduction reaction in the electrolysis cell directly affects the quality and yield of the aluminum produced, emphasizing the importance of controlling the conditions within the electrolytic cell.

Aluminum Electrolysis

Aluminum electrolysis is the industrial method used to extract aluminum from its oxide form, alumina. This process is primarily undertaken by the Hall-Héroult process, which is an electrolytic technique. It involves several key components: - **Electrolyte**: A molten bath of cryolite mixed with alumina. - **Anodes**: Carbon electrodes immersed in the bath. - **Cathode**: Where the aluminum ions gather to undergo reduction. During electrolysis, a direct current is passed through the cryolite, causing aluminum ions to be attracted to the cathode. Here, they receive electrons and form molten aluminum which can be collected. This process is not only vital because it allows the extraction of aluminum metal but also due to its economic and industrial significance. Aluminum electrolysis is energy-intensive, making it crucial to optimize the process to lower costs and enhance efficiency. Understanding the electrochemical principles, like cathode reactions and reduction processes, is essential for improving the overall efficiency of aluminum production.