(64) (18th of 19 Chapters) Electrolysis - GCE O Level Chemistry Lecture

Applications of Electrolysis in Industry

Purification of Metals

Purpose:

Electrolysis is employed primarily to purify metals and recover valuable materials from ores and recycled products, enhancing their quality and usability in industry.

Process Overview:

• Electrode Arrangement:

  • The impure metal serves as the anode.

  • The pure metal, often in the form of a starter sheet, acts as the cathode.

• Current Passage:

  • An electric current is passed through an electrolyte solution, typically composed of metal salts.

  • This current facilitates the dissolution of the impure metal at the anode and the deposition of pure metal at the cathode.

Example with Copper:

• During the electrolysis of copper(II) sulfate solution using copper electrodes:

  1. The copper anode gradually dissolves, releasing copper ions (Cu²⁺) into the electrolyte.

  2. These copper ions migrate toward the cathode, where they undergo reduction and are deposited as pure copper.

  3. Impurities such as other metals or non-metals accumulate as sludge at the anode, which can be collected for further processing or disposal, thereby enhancing efficiency and sustainability of metal production.

Electroplating

Purpose:

Electroplating is a technique used to enhance the aesthetic appeal and protect objects from corrosion. By depositing a layer of metal over the object, it can achieve improved durability and a reflective, attractive finish.

Process Overview:

• Electrode Arrangement:

  • The object intended for plating is connected to the cathode.

  • The anode is made of the metal that is to be deposited on the object, providing a source of metal ions.

• Electrolyte: This solution contains metal ions corresponding to the metal of the anode.

Example with Chromium:

• In the process of chrome plating a tap:

  1. A chromium anode is used in conjunction with a solution of chromium sulfate as the electrolyte.

  2. Chromium ions are released into the electrolyte and migrate toward the cathode, chemically reducing and depositing as a thin layer of chromium on the tap.

  3. This plating not only enhances the appearance but also provides a resistant surface against scratches and corrosion.

Simple Cells

Function:

Simple cells serve to convert chemical energy stored in the reactants into electrical energy, powering devices and electronics.

Example of Zinc-Copper Cell:

• In a basic zinc-copper galvanic cell:

  1. Zinc acts as the anode, where it is oxidized into zinc ions (Zn²⁺), releasing electrons.

  2. Copper acts as the cathode, where it accepts electrons from the anode, and simultaneously reduces hydrogen ions in the electrolyte to hydrogen gas (H₂).

Electric Current Generation:

• The flow of electrons from the anode to the cathode generates an electric current, which can be harnessed to power various devices.

Efficiency Factors:

• Efficiency is influenced by several factors including the types of electrodes used, the concentration and type of electrolyte, and the overall design of the cell.

Unique Simple Cell Example:

• Electrolyte Change:

  • Utilizing CuSO₄ (copper(II) sulfate) instead of H₂SO₄ (sulfuric acid); zinc remains as the anode and copper as the cathode.

• Ion Discharge Behavior:

  • Copper ions (Cu²⁺) are preferentially discharged over hydrogen ions (H⁺) due to their higher reactivity and lower reduction potential.

• Process Steps:

  1. Zinc oxidizes and releases electrons that flow towards the copper electrode.

  2. Copper ions in the electrolyte accept these electrons and are reduced, resulting in the deposition of copper around the cathode.

  3. The voltage generated by the cell is determined by the differences in reactivities between the metals involved, with zinc and copper yielding approximately 1.1 volts.

Electrolysis Checkpoints

Checkpoint Questions Evaluation and Examples:

• Question 1:

  • Evaluate the intensity of blue color in cells with different electrodes (platinum vs. copper).

    • Identified Cells: Copper electrodes (Y and Z) maintain a blue color due to the presence of Cu²⁺ ions, while platinum electrodes (W and X) do not exhibit this color change, indicating no ionic activity related to copper ions.

• Question 2:

  • Analyze mass differences between electrodes (Q and S) concerning heavier cation deposits.

    • Explanation involves heavier cations, like silver (Ag⁺), leading to a greater mass increase on respective electrodes, as these ions are reduced and deposited.

• Question 3:

  • Discuss the formation of a yellow streak from Ag⁺ and I⁻ ions.

    • Reasoning behind the streak formation involves the mobility of ions and differences in reactivity, with Ag⁺ migrating faster than I⁻, resulting in the formation of a yellow precipitate closer to the cathode.

Conclusion

The importance of electrolysis in industrial applications cannot be overstated, as it plays a critical role in metal purification, electroplating, and electrical energy generation. A comprehensive understanding of these processes is essential for students and professionals in the field of chemistry, contributing to advancements across various industries.