Problem 172 - A Complete Resource Book in Chemistry for JEE Main

Question

During the process of electrolytic refining of copper some metals present as impurity settle as anode mud. These are (a) \(\mathrm{Ag}\) and \(\mathrm{Au}\) (b) \(\mathrm{Pb}\) and \(\mathrm{Zn}\) (c) \(\mathrm{Fe}\) and \(\mathrm{Ni}\) (d) \(\mathrm{Sn}\) and \(\mathrm{Ag}\)

Step-by-Step Solution

Answer

The metals that settle as anode mud in copper refining are silver (Ag) and gold (Au).

Step 1: Understand Electrolytic Refining

Electrolytic refining is a process that uses electrolysis to purify metals by placing an impure metal, referred to as the anode, in an electrolyte solution while a pure metal acts as the cathode. When electricity passes through the cell, the pure metal is deposited at the cathode.

Step 2: Examine Impurities During Refining of Copper

In the electrolytic refining of copper, impurities in the anode can be broken down into two groups. Some are less noble than copper and dissolve into the solution, whereas others that are more noble than copper, such as gold (Au) and silver (Ag), do not dissolve and settle as anode mud (or slime).

Step 3: Identify the Metals in Anode Mud

Based on the refining process, metals that are more noble than copper, such as silver (Ag) and gold (Au), do not dissolve in the electrolyte and thus precipitate as anode mud.

Step 4: Select the Correct Answer

Among the given options, identify which metals align with being noble and able to settle as anode mud during the electrolytic refining of copper. The correct metals are silver (Ag) and gold (Au).

Key Concepts

Impurities in Electrolytic Refining

In the process of electrolytic refining of metals, impurities often play a crucial role in determining both the efficiency and the outcome of the operation. Electrolytic refining involves the use of electricity to purify metals through electrolysis. In this process, the impure metal is used as the anode and a strip of pure metal serves as the cathode. An electrolyte solution facilitates the movement of ions.

Impurities present during this refining stage are typically divided into two categories:

• Less noble metals: These are metals that are less resistant to corrosion and oxidation compared to the base metal being refined. They tend to dissolve in the electrolyte solution.
• More noble metals: These metals, such as gold (Au) and silver (Ag), do not dissolve during the refining process due to their higher resistance. They eventually settle as anode mud.

Understanding the behavior of these impurities is essential, as it determines how they will be managed during the refining process. The separation of impurities ensures the production of high-purity metal, which is the main goal of electrolytic refining.

Anode Mud

During electrolytic refining, particularly in the purification of copper, a byproduct known as anode mud is formed. Anode mud consists of the more noble impurities that do not dissolve into the electrolyte. These impurities sink to the bottom of the electrochemical cell.

Anode mud is valuable because it often contains precious metals such as:

• Silver (Ag)
• Gold (Au)

These metals are more noble than copper, indicating that they have a higher potential and do not dissolve in the electrolyte solution. Instead, these metals remain as solid residues which are then collected as anode mud.

The collection of anode mud is important in electrolytic refining because it allows for the recovery of these valuable metals, which can then be further processed or sold. By managing and extracting materials from anode mud, industries can improve the economic efficiency of the refining process.

Electrolysis in Metal Purification

Electrolysis is a foundational technique used in the purification of metals, such as copper. It involves using an electric current to drive a chemical reaction that separates pure metal from its impurities.

The basic setup includes:

• Anode: Made from the impure metal, this is where the metal starts before being purified.
• Cathode: A sheet of pure metal where the purified metal is deposited.
• Electrolyte: A suitable ionic solution that allows the passage of electricity and facilitates metal ion movement.

By sending electrical current through this setup, ions in the electrolyte move towards their respective electrodes. Pure metal ions from the anode dissolve into the solution, and then they travel to the cathode where they gain electrons and deposit as solid metal.

This process not only helps in achieving high purity levels but also enables the separation and collection of both less noble metals that dissolve into the electrolyte and more noble metals that form anode mud. Electrolysis is widely favored in the industry due to its effectiveness and ability to recover valuable metals from impurities.