Cathode Reaction In Zn/Ni Galvanic Cell Explained

by Andrew McMorgan 50 views

Zn(s) | Zn2+(aq) || Ni2+(aq) | Ni(s)

A. Ni2+(aq)+2e- β†’ Ni(s) B. Ni(s) β†’ Ni2+(aq) + 2e- C. Zn2+(aq)+2e- β†’ Zn(s) D. Zn(s) β†’ Zn2+(aq) + 2e-

Let's break down this electrochemistry question, guys, and figure out what's happening at the cathode of this galvanic cell. We'll walk through the basics of galvanic cells, oxidation-reduction reactions, and how to identify the cathode. By the end of this article, you'll not only know the answer but also understand the underlying principles. Let's dive in!

Understanding Galvanic Cells

First, let's get a handle on what a galvanic cell is. A galvanic cell, also known as a voltaic cell, is an electrochemical cell that uses spontaneous redox reactions to generate electrical energy. These cells are the foundation of batteries, converting chemical energy into electrical energy that we can use to power our devices. Understanding how these cells work involves grasping the concepts of oxidation and reduction.

Oxidation and Reduction

Redox reactions are at the heart of galvanic cells. Oxidation is the loss of electrons, while reduction is the gain of electrons. These two processes always occur together; one substance can't be oxidized unless another is reduced, and vice versa. In our shorthand notation, we need to identify which species is being oxidized and which is being reduced.

Cell Notation

The cell notation given, Zn(s) | Zn2+(aq) || Ni2+(aq) | Ni(s), is a shorthand way of representing the galvanic cell. Here's what each part means:

  • The single vertical lines (|) represent a phase boundary, such as between a solid electrode and an aqueous solution.
  • The double vertical lines (||) represent the salt bridge, which allows the flow of ions to maintain charge neutrality in the cell.
  • The species on the left side of the salt bridge represent the oxidation half-cell (anode), and the species on the right side represent the reduction half-cell (cathode).

Identifying the Cathode

So, how do we pinpoint the cathode in this setup? Remember, the cathode is where reduction occurs. In other words, it's where a chemical species gains electrons. Looking at our cell notation, Zn(s) | Zn2+(aq) || Ni2+(aq) | Ni(s), the right side of the salt bridge tells us what's happening at the cathode.

Nickel's Role at the Cathode

On the right side, we have Ni2+(aq) | Ni(s). This indicates that nickel ions (Ni2+) in the aqueous solution are being converted into solid nickel (Ni). For this to happen, the nickel ions must gain electrons. The half-reaction at the cathode, therefore, involves Ni2+ gaining two electrons to become Ni.

Writing the Half-Reaction

The half-reaction for the reduction of nickel ions to solid nickel is:

Ni2+(aq) + 2e- β†’ Ni(s)

This equation shows that nickel ions in the aqueous solution gain two electrons to form solid nickel, which plates onto the nickel electrode. This is the reduction process, and it occurs at the cathode.

Analyzing the Options

Now that we know what's happening at the cathode, let's look at the answer choices:

A. Ni2+(aq) + 2e- β†’ Ni(s) B. Ni(s) β†’ Ni2+(aq) + 2e- C. Zn2+(aq) + 2e- β†’ Zn(s) D. Zn(s) β†’ Zn2+(aq) + 2e-

Why Option A is Correct

Option A, Ni2+(aq) + 2e- β†’ Ni(s), perfectly matches what we determined is happening at the cathode. Nickel ions are gaining electrons to form solid nickel. This is reduction, and it occurs at the cathode.

Why Other Options are Incorrect

Let's examine why the other options are incorrect:

  • Option B: Ni(s) β†’ Ni2+(aq) + 2e- This equation shows nickel solid being oxidized to nickel ions, which means nickel is losing electrons. This is oxidation, not reduction, and it occurs at the anode, not the cathode.
  • Option C: Zn2+(aq) + 2e- β†’ Zn(s) This equation represents the reduction of zinc ions to solid zinc. While this is a reduction reaction, it's happening in the zinc half-cell (at the anode), not the nickel half-cell (at the cathode).
  • Option D: Zn(s) β†’ Zn2+(aq) + 2e- This equation shows zinc solid being oxidized to zinc ions, which means zinc is losing electrons. This is the oxidation reaction occurring at the anode.

The Anode Reaction

Just for completeness, let's briefly discuss what's happening at the anode. In this galvanic cell, the anode is where oxidation occurs. According to the cell notation, Zn(s) | Zn2+(aq), solid zinc is being converted into zinc ions in the aqueous solution. This means zinc is losing electrons. The half-reaction at the anode is:

Zn(s) β†’ Zn2+(aq) + 2e-

This equation shows that solid zinc is oxidized to zinc ions, releasing two electrons in the process. These electrons then flow through the external circuit to the cathode, where they are used to reduce nickel ions.

Final Answer

Alright, guys, after breaking down the components of the galvanic cell and understanding the roles of oxidation and reduction, we've pinpointed the half-reaction occurring at the cathode. The correct answer is:

A. Ni2+(aq) + 2e- β†’ Ni(s)

This reaction shows nickel ions gaining electrons to form solid nickel, which is the reduction process that defines the cathode in this galvanic cell. Understanding these principles not only helps in answering questions but also in grasping the fundamental concepts of electrochemistry.