Problem 108 - Chemistry An Atoms First Approach

Question

Copper can be plated onto a spoon by placing the spoon in an acidic solution of \(\mathrm{CuSO}_{4}(a q)\) and connecting it to a copper strip via a power source as illustrated below: a. Label the anode and cathode, and describe the direction of the electron flow. b. Write out the chemical equations for the reactions that occur at each electrode.

Step-by-Step Solution

Answer

In this electroplating process, the copper strip serves as the anode and the spoon serves as the cathode. Electrons flow from the copper strip (anode) to the spoon (cathode) through the power source. At the anode, oxidation occurs, and the half-reaction is: \(\mathrm{Cu(s) \rightarrow Cu^{2+}(aq) + 2e^{-}}\). At the cathode, reduction occurs, and the half-reaction is: \(\mathrm{Cu^{2+}(aq) + 2e^{-} \rightarrow Cu(s)}\).

Step 1: Identify the Anode and Cathode

Firstly, we need to identify which of the two electrodes is the anode and which is the cathode. The anode is the electrode where oxidation occurs, and the cathode is the electrode where reduction occurs. In the given process, the copper strip loses its copper ions by providing them to the acidic solution of \(\mathrm{CuSO}_{4}\). Therefore, the copper strip is the anode. The spoon, on the other hand, gains copper ions from the solution and is plated with copper. Hence, the spoon serves as the cathode.

Step 2: Determine Electron Flow Direction

Now, we should describe the direction of electron flow in the circuit. Electrons always flow from anode to cathode in an electrochemical cell. So, the electrons flow from the copper strip (anode) to the spoon (cathode) through the power source (battery).

Step 3: Write Chemical Equations for Anode Reaction

At the anode (copper strip), we have an oxidation process, where the solid copper metal loses electrons to become copper ions which go into the solution. The half-reaction for this process can be written as: \[ \mathrm{Cu(s) \rightarrow Cu^{2+}(aq) + 2e^{-}}\]

Step 4: Write Chemical Equations for Cathode Reaction

At the cathode (spoon), we have a reduction process, where copper ions from the solution gain electrons and become solid copper metal, depositing on the spoon. The half-reaction for this process can be written as: \[ \mathrm{Cu^{2+}(aq) + 2e^{-} \rightarrow Cu(s)}\] These are the chemical reactions occurring at each electrode during the electroplating process.

Key Concepts

Electrochemical Cell

An electrochemical cell is a device that can generate electrical energy from chemical reactions or facilitate chemical reactions through the introduction of electrical energy. In the scenario of electroplating a spoon with copper, the cell includes two electrodes: the anode and the cathode, submerged in an acidic solution of copper sulfate (\( \mathrm{CuSO}_{4} \)).

• The **anode** is the copper strip, where oxidation takes place, meaning that copper metal loses electrons.
• The **cathode** is the spoon, where reduction happens, allowing copper ions to gain electrons and deposit as solid copper.

This creates a flow of electrons through the external circuit from the anode to the cathode. The electrolyte, \( \mathrm{CuSO}_{4} \) solution, allows ions to move and balance the charges resulting from electron transfer. Understanding the parts of an electrochemical cell helps us see how materials are moved at a microscopic level in processes like electroplating.

Oxidation and Reduction

For electroplating to work, it's essential to understand oxidation and reduction, also known as redox reactions. These reactions are all about the transfer of electrons:

• **Oxidation** occurs at the anode. This means that copper atoms on the copper strip lose electrons and go into the solution as copper ions:\[ \mathrm{Cu(s) \rightarrow Cu^{2+}(aq) + 2e^{-}}\]
• **Reduction** takes place at the cathode, where copper ions from the solution gain electrons and turn into solid copper, which deposits on the spoon:\[ \mathrm{Cu^{2+}(aq) + 2e^{-} \rightarrow Cu(s)}\]

In redox reactions, the loss of electrons is oxidation, and the gain of electrons is reduction. These reactions are simultaneous and help with tasks like metal plating, where we coat one material with another using electricity.

Electron Flow

Electron flow is the movement of electrons through an electrical circuit. In electroplating, this flow is crucial as it facilitates the redox reactions, enabling metals to deposit onto surfaces. Electrons always flow from the anode to the cathode.

• At the **anode**, electrons are provided by the oxidation of copper metal.
• They travel through the external circuit, driven by a power source, to the **cathode**.
• At the **cathode**, these electrons participate in the reduction of copper ions, leading to metal deposition.

Understanding electron flow in electrochemical cells is vital for controlling processes like electroplating. This principle is used to manipulate materials at the atomic level, enabling various technological applications.