Electrolytic purification of copper and aluminium

 

Electrolysis of copper involves the use of electrical energy to drive a non-spontaneous redox reaction, resulting in the deposition of copper metal at the cathode and the dissolution of copper ions at the anode. This process is commonly employed in the purification and electroplating of copper.

Here's a step-by-step explanation of the electrolysis of copper, along with examples:

Electrolysis of Copper Sulfate Solution:

1. Setup:

• A copper sulfate ($CuSO_4$) solution is commonly used. The electrolytic cell consists of two electrodes (usually copper rods), a power supply, and a solution of copper sulfate.

2. Electrodes:

• The anode is typically made of impure copper, and the cathode is made of a pure copper rod.

3. Reactions:

• At the anode: $\text{Cu} \rightarrow \text{Cu}^{2+} + 2e^-$
• At the cathode: $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$

4. Process:

• When an electric current is passed through the copper sulfate solution, copper ions ($Cu^{2+}$) migrate to the cathode and gain electrons, forming solid copper ($Cu$) that plates onto the cathode.
• At the anode, copper metal dissolves into copper ions, maintaining the concentration of copper ions in the solution.

5. Overall Reaction:

• $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$

6. Impurities:

• Impurities present in the impure copper anode remain in the solution or may form a sludge, leaving the pure copper to plate out on the cathode.

7. Application - Electroplating:

• Electrolysis of copper is used in electroplating processes where a thin layer of copper is deposited onto the surface of another metal. For example, electroplating a steel object with copper for decorative or protective purposes.

8. Faraday's Laws:

• The amount of copper deposited at the cathode is proportional to the quantity of electricity passed through the cell, as described by Faraday's laws of electrolysis.

9. Observations:

• Over time, the cathode will become coated with a layer of solid copper, and the anode may show signs of corrosion as it loses mass.

Example Calculation:

If a current of 2.0 amperes is passed through a copper sulfate solution for 2 hours, calculate the mass of copper deposited at the cathode.

Solution:

• First, calculate the total charge passed (Q) using the formula $Q = I \cdot t$, where $I$ is the current (2.0 A) and $t$ is the time in seconds (2 hours converted to seconds).
• Use Faraday's constant to relate charge to moles of electrons and then determine the moles of copper deposited.
• Finally, use the molar mass of copper to find the mass deposited.

This example illustrates the quantitative aspect of the electrolysis of copper and how the amount of deposited copper is related to the electric charge passed through the system.

Certainly! Here are 20 questions on the electrolytic purification of copper and aluminum, along with explained answers:

1. Q: What is the primary purpose of electrolytic purification in the extraction of metals like copper and aluminum?

A: Electrolytic purification is used to refine impure metals by using electrolysis to remove any remaining impurities and produce high-purity metals.

2. Q: In the electrolytic purification of copper, what is the role of the anode and cathode?

A: The impure copper is used as the anode, and pure copper is deposited at the cathode. The anode dissolves, releasing copper ions into the electrolyte.

3. Q: What electrolyte is commonly used in the electrolytic purification of copper?

A: Copper sulfate solution is typically used as the electrolyte in the purification of copper.

4. Q: Why is it important to ensure that the anode in copper purification is impure copper?

A: The impure copper anode ensures a continuous supply of copper ions into the electrolyte, allowing for the continuous deposition of pure copper at the cathode.

5. Q: What is the purpose of adding a small amount of acid to the electrolyte in copper purification?

A: The acid helps to increase the conductivity of the electrolyte, facilitating the movement of ions in the solution.

6. Q: Explain the role of the copper ions in the electrolytic purification of copper.

A: Copper ions are released from the anode, move through the electrolyte, and get deposited as pure copper at the cathode during the electrolytic purification process.

7. Q: What are the common impurities found in impure copper?

A: Impure copper can contain impurities such as iron, zinc, lead, and other metals.

8. Q: Why does the impure copper anode gradually decrease in size during the electrolytic purification process?

A: The impure copper anode dissolves as copper ions are released into the electrolyte, resulting in a gradual decrease in its size.

9. Q: What is the purpose of the porous pot in the electrolytic purification of copper?

A: The porous pot separates the anode and cathode compartments, preventing the mixing of impurities from the anode with the pure copper being deposited at the cathode.

10. Q: How is aluminum extracted, and what role does electrolysis play in its purification?

A: Aluminum is extracted from bauxite through the Bayer process, and electrolysis is used to purify the aluminum by removing impurities.

11. Q: In the electrolytic purification of aluminum, what materials are used as the anode and cathode?

A: The carbon lining of the electrolytic cell serves asthe cathode, and a graphite rod is used as the anode.

12. Q: What is the electrolyte used in the purification of aluminum through electrolysis?

A: Cryolite (sodium aluminum fluoride) is used as the electrolyte in the purification of aluminum.

13. Q: Why is the electrolyte in aluminum purification kept at a high temperature?

A: High temperatures are required to keep the electrolyte molten and facilitate the conductivity necessary for the electrolysis process.

14. Q: What is the purpose of adding alumina (aluminum oxide) to the electrolyte in aluminum purification?

A: Alumina is added to provide a source of aluminum ions for deposition at the cathode during electrolysis.

15. Q: Why is the anode in aluminum purification constantly replaced during the process?

A: The anode is consumed during the process as oxygen isevolved, and it needs to be regularly replaced to maintain the efficiency of the electrolytic cell.

16. Q: Explain the role of the graphite rods in the electrolytic purification of aluminum.

A: The graphite rods serve as the anode and participate inthe release of oxygen gas during the electrolysis ofaluminum.

17. Q: What are the environmental considerations associated with the electrolytic purification of metals like aluminum?

A: The process requires a significant amount of energy, often derived from fossil fuels, contributing toenvironmental concerns.

18. Q: How is the purity of the metals obtained through electrolytic purification determined?

A: The purity is determined through various analytical techniques, such as spectroscopy or chemical analysis, which assess the composition of the final metal product.

19. Q: What challenges are associated with the commercial production of aluminum through electrolysis?

A: High energy consumption, cost of raw materials, and environmental impact are significant challenges in the commercial production of aluminum through electrolysis.

20. Q: Can electrolytic purification be used for all metals, or are there specific criteria for its applicability?

A: Electrolytic purification is generally applicable tometals that can be deposited from an electrolyte. However, not all metals can be effectively purified using this method, and the choice depends on the specific characteristics of the metal and its compounds.