Question

Which of the following statement is true for the electrochemical, Daniel cell?

• A. Electrons flow from copper electrode to zinc electrode.
• B. Current flows from zinc electrode to copper electrode.
• C. Cation moves toward copper electrode.
• D. Cation moves toward zinc electrode.
• E. Reduction occurs at cathode.

Hint:

In a Daniell cell, oxidation occurs at the anode (zinc), and reduction occurs at the cathode (copper). Electrons flow from anode to cathode, while current flows from cathode to anode externally.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A Daniel cell is a specific type of electrochemical cell involving zinc and copper electrodes. Its standard representation is Zn(s) | Zn\(^{2+}\)(aq) || Cu\(^{2+}\)(aq) | Cu(s). To answer the question, we need to know the processes occurring at the anode and cathode, the direction of electron and current flow, and the movement of ions in the salt bridge.
Step 2: Detailed Explanation:
In a Daniel cell:

Anode (Oxidation): Zinc is more reactive than copper, so it gets oxidized. The zinc electrode is the anode (negative electrode).
Reaction: Zn(s) \(\rightarrow\) Zn\(^{2+}\)(aq) + 2e\(^-\)

Cathode (Reduction): Copper ions get reduced. The copper electrode is the cathode (positive electrode).
Reaction: Cu\(^{2+}\)(aq) + 2e\(^-\) \(\rightarrow\) Cu(s)

Based on this, let's analyze the options:

(A) Electrons flow from copper electrode to zinc electrode: Electrons are released at the zinc anode and consumed at the copper cathode. So, they flow from Zn to Cu in the external circuit. This statement is false.

(B) Current flows from zinc electrode to copper electrode: Conventional current flows in the opposite direction to the flow of electrons. Since electrons flow from Zn to Cu, the current flows from Cu to Zn. This statement is false.

(C) Cation moves toward copper electrode: The copper electrode is the cathode where positive Cu\(^{2+}\) ions are consumed, leaving an excess of negative ions (like SO\(_4^{2-}\)) in the solution. To maintain electrical neutrality, cations (positive ions like K\(^+\) or Na\(^+\)) from the salt bridge move into the cathode compartment (towards the copper electrode). This statement is true.

(D) Cation moves toward zinc electrode: The zinc electrode is the anode where positive Zn\(^{2+}\) ions are produced. To neutralize this excess positive charge, anions (negative ions) from the salt bridge move towards the zinc electrode. This statement is false.

(E) Reduction occurs at cathode: By definition, the electrode where reduction takes place is called the cathode. In the Daniel cell, reduction of Cu\(^{2+}\) ions occurs at the copper electrode, which is the cathode. This statement is true.

Step 3: Final Answer:
Both statements (C) and (E) are true for a Daniel cell. Statement (E) is a fundamental definition true for all electrochemical cells, while statement (C) is a specific consequence of the process at the cathode in a Daniel cell. Since a multiple-choice question should ideally have only one correct answer, the presence of two correct options is likely why the question was cancelled in the official exam.