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) \(\mathrm{Sn}\) and \(\mathrm{Ag}\)

Step-by-Step Solution

Answer

The correct answer is (a) 1{Ag}1 and 1{Au}1.

Step 1: Understanding Electrolytic Refining

Electrolytic refining is a process used to purify metals. In the case of copper, impure copper is used as the anode and pure copper is deposited on the cathode. During this process, noble metals, which are often impurities and do not dissolve in the copper sulfate solution, settle down below the anode as anode mud.

Step 2: Identifying Noble Metals

In electrolytic refining, noble metals such as silver (1{Ag}1) and gold (1{Au}1) do not dissolve in the electrolyte solution because they are less reactive. Instead, they settle at the bottom of the cell as part of the anode mud.

Step 3: Evaluating Given Options

Option (a) lists metals 1{Ag}1 and 1{Au}1, which are noble metals. Option (b) lists 1{Pb}1 and 1{Zn}1, which are more reactive and don't form anode mud. Option (c) lists 1{Fe}1 and 1{Ni}1, which also dissolve in the electrolyte solution. Option (d) lists 1{Sn}1 and 1{Ag}1; 1{Ag}1 is noble, but 1{Sn}1 is reactive and doesn't form anode mud.

Step 4: Choosing the Correct Answer

Since 1{Ag}1 and 1{Au}1 are noble metals that settle as anode mud during the refining of copper, option (a) is the correct answer.

Key Concepts

Copper Purification

Electrolytic refining is a popular method used to purify copper. This process involves using an impure copper anode and a pure copper cathode, with an electrolyte solution like copper sulfate. When an electric current passes through the electrolyte, pure copper ions from the anode dissolve into the solution and are deposited onto the cathode, resulting in pure copper formation.
The process not only purifies copper but also separates impurities effectively. During the refining, useful and valuable metals can be recovered in their purest form. Electrolytic refining is highly efficient and capable of producing high-purity copper. Industries and manufacturing sectors rely heavily on this technique.
Some key points include:

• The anode is made from impure copper.
• The cathode comprises pure copper.
• The solution is typically copper sulfate.
• Impure copper dissolves, and pure copper plates the cathode.

Anode Mud

In the copper purification process, not all impurities in the impure copper anode dissolve in the electrolyte solution. Some of the impurities are noble metals, which are chemically stable and less reactive. These metals do not take part in the electrolysis and, therefore, settle at the bottom of the electrolytic cell, forming what is known as anode mud.
Anode mud is a valuable byproduct as it contains noble metals such as silver and gold, which can be extracted and sold for profit. The presence of these noble metals increases the economic value of the anode mud. Refining this mud can contribute significantly to the profitability of copper purification processes.
Understanding the composition of anode mud is crucial:

• Noble metals that do not react in the solution are present.
• Silver and gold are common elements in anode mud.
• It's a byproduct that holds economic value.

Noble Metals

Noble metals play a significant role in the process of electrolytic refining of copper. These metals are named so because of their exceptional stability and resistance to corrosion and oxidation. Their noble qualities mean they do not react easily in the copper sulfate solution during the refining process.
Common noble metals include silver (Ag) and gold (Au), among others. In the context of copper refining, these metals are impurities that don't dissolve with the copper ions. Instead, they faithfully remain in the form of anode mud, waiting to be recovered separately. Their chemical properties make them invaluable throughout various industries, mainly due to their durability and rarity.
Key aspects of noble metals are:

• They are less reactive compared to other metals.
• Silver and gold are examples that settle as anode mud.
• Their chemical inertness adds to their value and demand.