Problem 147 - A Complete Resource Book in Chemistry for JEE Main

Question

For the electrolysis of \(\mathrm{CuSO}_{4}\) solution which is/are correct? (a) Cathode reaction: \(\mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}\) using \(\mathrm{Cu}\) electrode (b) Anode reaction: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2}++2 \mathrm{e}^{-}\)using \(\mathrm{Cu}\) electrode (c) Cathode reaction: \(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}\) using \(\mathrm{Pt}\) electrode (d) Anode reaction: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+{ }^{2}}+2 \mathrm{e}^{-}\)using \(\mathrm{Pt}\) electrode

Step-by-Step Solution

Answer

Options (a) and (b) are correct.

Step 1: Understanding Electrolysis Basics

In electrolysis, the cathode is where reduction occurs, and the anode is where oxidation occurs. For [ ext{CuSO}_4 ext{ solution}] with copper electrodes, copper from the solution is deposited at the cathode, and copper from the anode dissolves into the solution.

Step 2: Cathode Reaction Analysis

For a copper ([ ext{Cu}]) electrode in a [ ext{CuSO}_4 ext{ solution}], the appropriate cathode reaction is [ ext{Cu}^{2+} + 2 ext{e}^{-} ightarrow ext{Cu}], where copper ions are reduced to solid copper.

Step 3: Anode Reaction Analysis

At the anode with a copper electrode, the copper dissolves into the solution as [ ext{Cu} ightarrow ext{Cu}^{2+} + 2 ext{e}^{-}], creating copper ions. This corrects the balance of copper lost at the cathode.

Step 4: Analyzing Reactions with Platinum Electrodes

Using a platinum (Pt) electrode changes the reactions. At the cathode, hydrogen ions can be reduced to form [2 ext{H}^{+} + 2 ext{e}^{-} ightarrow ext{H}_2]. At the anode, with an inert Pt electrode, water is typically decomposed rather than copper being oxidized.

Step 5: Conclusion of Correct Options

Based on the analysis, option (a) is correct for the cathode reaction using copper electrodes, and option (b) is the correct anode reaction with copper electrodes. Options (c) and (d) involve a different setup and are incorrect in this context.

Key Concepts

Copper Electrodes

In the electrolysis of copper sulfate ( ₄) solution, copper electrodes play an essential role. Copper electrodes ensure that copper ions in the solution are continuously exchanged. At the cathode, a copper electrode permits copper ions ( ²⁺) to gain electrons and deposit as metallic copper. This provides a simple and effective way to gather pure copper. On the other hand, at the anode, the copper electrode maintains the balance by losing copper to the solution as ions. This means copper from the electrode itself dissolves into the solution, turning into ₂₊ ions.

• Using copper electrodes is significant as they actively participate in the electrolysis reactions, ensuring consistent transfer of copper.
• They help in maintaining a neutral concentration of ions within the solution.

Cathode Reaction

During electrolysis, the cathode is the site of reduction reactions. In our setup with copper electrodes, the primary cathode reaction is the reduction of copper ions from the solution. The reaction is given by:\[\text{Cu}^{2+} + 2\text{e}^{-} \rightarrow \text{Cu}\] This means that copper ions from the ₄ solution gain two electrons and form solid copper, depositing on the electrode.

• The reduction reaction contributes to the formation of a pure copper layer on the cathode.
• This process is efficient for copper purification as it directly transfers copper ions from the solution to a solid state.

Anode Reaction

The anode, in the context of the electrolysis of ₄ with copper electrodes, is where oxidation occurs. Here, the copper metal from the anode itself is oxidized, contributing ions back into the solution. This reaction is expressed as:\[\text{Cu} \rightarrow \text{Cu}^{2+} + 2\text{e}^{-}\]

• The anode reaction ensures that copper ions are replenished in the solution as copper dissolves away from the electrode surface.
• This process keeps the concentration of copper ions relatively stable, ensuring the cathode can continue its reduction process effectively.

Together, these reactions at the anode and cathode create a seamless cycle of copper ion exchange during electrolysis.