Question

Jewelry is often manufactured by plating an expensive metal such as gold over a cheaper metal. How might such a process be set up as an electrolysis reaction?

Short answer

To set up an electrolysis process for gold plating, follow these steps: 1) Choose an electrolyte solution containing gold ions such as gold(III) sulfate (\(\text{Au}_2(\text{SO}_4)_3\)) or gold(III) chloride (\(\text{AuCl}_3\)). 2) Prepare an anode made of gold and a cathode made of the cheaper metal to be plated. 3) Connect the anode to the positive terminal and cathode to the negative terminal of a DC power supply. 4) Submerge the electrodes into the electrolyte solution and ensure they don't touch each other. 5) Turn on the power supply and adjust the voltage as needed (typically 1-3V) to plate the gold ions onto the cheaper metal's surface. 6) Allow the process to continue for a sufficient time to achieve the desired thickness, and monitor the voltage and electrodes. 7) Once completed, rinse the gold-plated metal and gently dry it.

Step-by-step solution

Understand the concept of electrolysis

Electrolysis is a chemical process where an electric current is passed through a solution containing ions to break down the compounds and separate the ions. In the case of plating jewelry, this process is used to deposit a thin layer of a precious metal like gold onto the surface of a cheaper metal.

Identifying the metals involved in the process

In this exercise, we will consider gold as the precious metal to be plated onto the surface of a cheaper metal, such as copper or brass. The gold will be used as an anode, and the cheaper metal as the cathode.

Choosing an appropriate electrolyte solution

To perform electrolysis, we need an electrolyte solution that can carry gold ions from the anode to the cathode. A suitable electrolyte for plating gold would be a solution containing gold ions such as gold(III) sulfate (\(\text{Au}_2(\text{SO}_4)_3\)) or gold(III) chloride (\(\text{AuCl}_3\)).

Preparing the electrodes

For the electrolysis process, we need an anode made of gold and a cathode made of the cheaper metal. Clean the surface of both the electrodes before placing them in the electrolyte solution to ensure proper adhesion of the gold layer onto the cheaper metal during the process.

Setting up the electrolysis process

To set up the electrolysis process, follow these steps: 1. Pour the selected electrolyte solution containing gold ions into a beaker. 2. Connect the anode (gold electrode) to the positive terminal of a DC power supply and the cathode (cheaper metal electrode) to the negative terminal. 3. Submerge both anode and cathode into the electrolyte solution, ensuring that they do not touch each other. 4. Turn on the power supply and adjust the voltage as needed (typically around 1-3V is required for gold plating). The flow of electric current will cause gold ions to migrate from the anode and get deposited onto the cathode surface.

Allow time for plating and monitoring the process

Allow the electrolysis process to continue for an adequate time to ensure a thin and even layer of gold on the cheaper metal. The duration of the process depends on the desired thickness of the gold layer. During the process, monitor the electrodes and voltage to ensure smooth plating.

Finishing the process and cleaning the plated jewelry

Once the desired thickness of the gold layer is achieved, turn off the power supply, and carefully remove the cathode (now gold-plated) from the electrolyte solution. Rinse it thoroughly with distilled water to remove any residual electrolyte solution and gently dry the jewelry with a soft cloth. Through these steps, the electrolysis reaction can be set up to plate an inexpensive metal such as copper or brass with gold, resulting in gold-plated jewelry.

Key concepts

Electrolysis Process

Electrolysis is a fascinating and central process in many industrial applications, including the production of gold-plated jewelry. To understand how it works, imagine a cell composed of two electrodes immersed in a liquid that contains ions—this liquid is known as the electrolyte solution. When an electric current is applied through the electrodes, the ions in the solution start to move. Cations, which are positive ions, migrate towards the cathode (the negative electrode) and are reduced (gain electrons), while anions, which are negative ions, move towards the anode (the positive electrode) and are oxidized (lose electrons).

In the context of gold plating, the purpose of electrolysis is to transfer gold ions onto another metal's surface to create a coating. This is achieved by setting up the gold as the anode, which dissolves into gold ions that move through the electrolyte and get deposited onto the cathode made of a less precious metal. The result is a beautiful, gold-layered item, such as a piece of jewelry.

Gold Plating Chemistry

The chemistry behind gold plating is quite precise, involving the use of gold compounds that can easily give up their gold ions. When setting up gold for electrolysis, we employ gold(III) compounds like gold(III) sulfate (\r\(\text{Au}_2(\text{SO}_4)_3\)) or gold(III) chloride (\r\(\text{AuCl}_3\)). These compounds form part of the electrolyte solution and, upon applying an electric current, gold ions are released into the solution. As the process continues, these gold ions are reduced when they reach the negatively charged cathode and deposit as a thin layer of solid gold. This way, jewelry makers can apply a high-value finish to more common metallic items without the exorbitant cost of solid gold products.

Electric Current in Electrolysis

The role of electric current in electrolysis is of utmost importance, as it directly affects the efficiency and quality of the plating. To achieve gold plating, a direct current (DC) power supply is crucial. Once the circuit is complete, electric current flows through the electrodes, driving the gold ions from the anode to the cathode. The rate at which gold ions are deposited, which determines the thickness and uniformity of the plating, is adjustable through the voltage applied. Typically, a lower voltage ensures a slower, more controlled deposition, leading to a smoother and more even gold layer. It's important to fine-tune the voltage and current settings, as too high of a current can cause rapid plating with poor adhesion or even the formation of unwanted textures on the jewelry's surface.

Electrolyte Solution

A carefully chosen electrolyte solution is pivotal in gold plating. It serves as the medium through which gold ions travel from the anode to the cathode. The electrolyte must contain a soluble form of gold, hence gold(III) salts like \r\(\text{Au}_2(\text{SO}_4)_3\) or \r\(\text{AuCl}_3\) are often used. These compounds are chosen because they dissolve well in water and readily release gold ions under the influence of electric current. Furthermore, the solution must be conducive to the uniform flow of ions, which is why the concentration of the electrolyte is just as critical as its composition. If the solution is too dilute or too concentrated, it can impair the plating process, leading to uneven thickness or poor adhesion of the gold layer. Temperature is also a key factor, as it affects the electrolyte's conductivity and the rate of reaction, making it essential to maintain the solution at an optimal temperature during the entire plating operation.