In the electrolytic cell, flow of electrons is from — Electrochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Distinguish Between External and Internal Circuits in an Electrolytic Cell An electrolytic cell is composed of two distinct parts that form a complete closed electrical loop: 1. **The External Circuit (External Supply):** This consists of the metallic wires and the external direct current (DC) power source (such as a battery) connected to the electrodes. Here, charge is carried solely by mobile electrons. 2. **The Internal Circuit (Internal Supply):** This consists of the electrolyte solution (or molten salt) containing mobile cations and anions. Here, charge is carried by the physical migration of ions, as free electrons cannot exist stably in solution. Step 2 - Analyze Electron Flow in the External Circuit The external power source acts as an electron pump that establishes the polarities of the electrodes: * The negative terminal of the battery pushes electrons through the external wire into the cathode, making it negatively charged: $$\text{Electron flow: Negative terminal of battery} \rightarrow \text{Cathode}$$ * The positive terminal of the battery pulls electrons through the external wire from the anode, making it positively charged: $$\text{Electron flow: Anode} \rightarrow \text{Positive terminal of battery}$$ Thus, in the external circuit, the overall physical flow of electrons is from the **anode to the cathode** through the external supply. Step 3 - Analyze Effective Electron Flow in the Internal Circuit In the internal circuit (within the solution), the circuit is completed through chemical redox reactions occurring at the electrode surfaces: * **At the Cathode (Reduction):** Cations ($\ce{M^{n+}}$) migrate to the cathode and consume electrons from its surface: $$\ce{M^{n+}(aq) + n e^- -> M(s)}$$ * **At the Anode (Oxidation):** Anions ($\ce{A^{m-}}$) migrate to the anode and release electrons onto its surface: $$\ce{A^{m-}(aq) -> A(s) + m e^-}$$ Looking at this process from the perspective of charge balance and electron transfer: * Electrons are continuously consumed at the cathode and generated at the anode. * To complete the circuit internally, negative charge is transported through the solution from the cathode toward the anode by migrating anions ($\ce{A^{m-}}$). * Therefore, the chemical redox reactions and ionic migration serve as an **internal supply** of charge that effectively transfers electrons from the **cathode to the anode**. Step 4 - Evaluate and Explain the Options * **Option (A) is incorrect:** Free electrons cannot exist or travel freely inside an aqueous solution ("in solution") because they would immediately react with water or other species. The charge inside the solution is carried by ions. * **Option (B) is incorrect:** Through the external supply (the metallic wires), electrons physically flow from the anode to the cathode, not from the cathode to the anode. * **Option (C) is correct:** As explained in Step 3, the internal circuit (internal supply) completes the closed loop by effectively transferring negative charge (electrons) from the cathode to the anode via ionic migration and electrode reactions. * **Option (D) is incorrect:** While it is true that electrons flow from the anode to the cathode in the external supply, this represents the external circuit rather than the internal mechanism described by option (C). $$\text{Correct Option: } \boxed{\text{C}}$$