Problem 138 - 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) Sn and \(\mathrm{Ag}\)

Step-by-Step Solution

Answer

The metals that settle as anode mud are (a) Ag and Au.

Step 1: Understanding Electrolytic Refining

In electrolytic refining, impurities in the copper dissolve in the solution, but less reactive metals do not dissolve and settle at the bottom as anode mud. This includes metals that are less reactive than copper.

Step 2: Identifying Reactive vs. Less Reactive Metals

Among the options given, metals like \(Fe,Zn, Ni, Pb, \) and \(Sn\) are more reactive than copper and would not settle as anode mud at the anode during electrolytic refining. Instead, metals like \(Ag\) (silver) and \(Au\) (gold), which are less reactive, do not dissolve and settle as anode mud.

Step 3: Comparing Options

Examine each given pair of metals to see if they are less reactive than copper. \(Ag\) and \(Au\) are both less reactive, whereas in other options, at least one metal is more reactive than copper will not settle as anode mud.

Step 4: Concluding the Correct Answer

Only option (a) \(\text{Ag and Au}\) contains metals that are less reactive than copper and would settle as anode mud during electrolytic refining. The other options include more reactive metals that would not settle as mud.

Key Concepts

Anode Mud in Electrolytic Refining

During electrolytic refining of copper, impurities play a crucial role in the process. An interesting phenomenon occurs when certain less reactive impurities do not dissolve in the electrolyte solution. Instead, they gather at the bottom of the cell, forming what is known as 'anode mud'. This mud consists of metals that are less reactive than copper, often including precious metals like silver (Ag) and gold (Au). Anode mud is significant not only because it indicates successful separation of materials but also because it can be collected and processed further to extract these valuable metals.
It's important to understand that the components of anode mud provide clues about the reactivity of the metals involved. In refining, more reactive metals dissolve first, while the less reactive ones settle as mud. This property is crucial for the purification of copper and enhances the economic value of the process.

Recognizing Less Reactive Metals

In the context of electrolytic refining, identifying less reactive metals is critical. These metals do not dissolve in the electrolyte during the purification process, unlike their more reactive counterparts.

• Silver (Ag)
• Gold (Au)

These metals are examples of elements that are less reactive than copper.
When you analyze the options given in the original exercise, metals such as iron (Fe), zinc (Zn), nickel (Ni), lead (Pb), and tin (Sn) emerge as more reactive than copper. Therefore, they won't settle as anode mud during the process. In contrast, Ag and Au, being less reactive, stay intact and form part of the anode mud.
Understanding these differences in reactivity helps in accurately identifying and utilizing each metal according to its chemical behavior during refining.

Copper Purification Process

Copper purification via electrolytic refining is a method used to upgrade the purity of copper extracted from ore. During this process, an electrolytic cell is set up where impure copper is made into the anode and pure copper is plated onto the cathode.
The choice of electrolyte is crucial – it can dissolve impurities while allowing pure copper to deposit as a solid on the cathode. Metals that are more reactive than copper dissolve in the electrolyte, but less reactive metals such as silver and gold remain undissolved and form anode mud. This results in a high purity level of copper, often exceeding 99% purity. This method not only refines copper efficiently but also recovers valuable precious metals from the anode mud, making the process economically beneficial.
In summary, understanding the reactivity of metals involved is vital for refining, as it dictates how and where each metal settles or dissolves during the purification process.