Problem 57 - Chemistry Matter and Change

Question

Down’s Cell What reaction takes place at the cathode when molten sodium chloride is electrolyzed?

Step-by-Step Solution

Answer

The reaction that takes place at the cathode when molten sodium chloride is electrolyzed is the reduction half-reaction: \( Na^+ + e^- \rightarrow Na \). This involves sodium ions (Na+) gaining an electron (e-) to become neutral sodium atoms (Na).

Step 1: 1. Identify the cation, anion, and electrodes

As mentioned earlier, in molten NaCl, the sodium ion (Na+) is the cation and the chloride ion (Cl-) is the anion. The electrodes in the electrolysis process are the cathode (negative electrode) and anode (positive electrode). e-left : function(cathode(x) );

Step 2: 2. Migrate the cations to the cathode

During electrolysis, the Na+ ions are attracted to the cathode due to its negative charge. This migration of ions is an essential step in the process since it leads to the reduction reaction that will happen at the electrode.

Step 3: 3. Write the reduction half-reaction at the cathode

The reduction half-reaction that takes place at the cathode can be represented as: Na+ + e^- -> Na This equation indicates that sodium ions (Na+) gain an electron (e^-) to become neutral sodium atoms (Na).

Step 4: 4. Confirm that the reaction taking place at the cathode is a reduction reaction

In a reduction half-reaction, the species, in this case, the sodium ions (Na+), gain electrons. As we can see in the equation: Na+ + e^- -> Na The sodium ions (Na+) are gaining an electron (e^-) and transforming into neutral sodium atoms (Na). This confirms that the reaction taking place at the cathode is a reduction reaction.

Step 5: Conclusion

The reaction that takes place at the cathode when molten sodium chloride is electrolyzed is the reduction half-reaction: Na+ + e^- -> Na This reaction involves the sodium ions (Na+) gaining an electron (e^-) to become neutral sodium atoms (Na).

Key Concepts

Cathode and Anode in Electrolysis

Understanding the roles of the cathode and anode during electrolysis is crucial for comprehending how this process works. Electrolysis is a method used to induce a chemical reaction through the application of electrical energy. The cathode is the negative electrode where the reduction reaction takes place. On the other hand, the anode is the positive electrode where oxidation occurs.

In the context of sodium chloride electrolysis, when molten, the positively charged sodium ions (Na+) migrate towards the cathode, where they receive an electron and become neutral sodium atoms. In general, the cathode attracts cations, or positively charged ions, while the anode attracts anions, or negatively charged ions. This movement of ions toward their respective electrodes is essential for the electrolysis to proceed.

Reduction Half-Reaction

The reduction half-reaction is a fundamental concept in electrolysis and electrochemistry. Reduction is a process where a substance gains electrons, which is indicated by a decrease in its oxidation state. In the case of the sodium chloride electrolysis, the reduction half-reaction at the cathode can be
expressed as:
\[ Na^+ + e^- \rightarrow Na \]
This simple equation shows that each sodium ion (Na+) accepts one electron (e^-) to form a neutral sodium atom (Na). This gain of electrons by sodium ions is a defining characteristic of the reduction process. By understanding this reaction, students can grasp the transformation of ions into their elemental form during electrolysis.

Migrating Ions During Electrolysis

The migration of ions during the electrolysis of sodium chloride is an integral part of the process. Ions move towards electrodes where they can undergo the necessary reactions to form the desired products. For example, in the electrolysis of molten NaCl, Na+ ions move toward the cathode, while Cl- ions move toward the anode.

The sodium ions (Na+), which are cations, are attracted to the negatively charged cathode where they will be reduced, as described in their respective half-reaction. Conversely, the chloride ions (Cl-), as anions, move toward the positively charged anode where they will be oxidized and release electrons to complete the circuit. This movement is driven by the applied electrical potential that encourages the ions to travel towards the oppositely charged electrode.