Electrolytic Refining: Assertion & Reason Analysis

This question asks us to evaluate two statements, an Assertion (A) and a Reason (R), related to the process of electrolytic refining.

Refining Process Explained

Electrolytic refining is a method used to purify metals to a very high degree. Here's a quick overview:

• Anode: Made of the impure metal.
• Cathode: Made of a thin strip of pure metal.
• Electrolyte: A solution containing ions of the metal being purified.

When electricity passes through, the impure anode dissolves, and pure metal deposits onto the cathode.

Assertion (A): Impurity Settling Verified

Statement (A): In electrolytic refining, insoluble impurities settle down at the bottom of the anode.

This statement is true. During electrolytic refining, the impure anode dissolves. However, some impurities present in the anode might be less reactive or insoluble in the electrolyte. These insoluble materials do not dissolve or participate in the electrochemical process. As the anode block dissolves away, these insoluble impurities detach and fall to the bottom of the electrolytic cell. This collection of settled impurities is often referred to as 'anode mud' or 'anode sludge'.

Reason (R): Impurity Insolubility Verified

Statement (R): These impurities do not dissolve in the electrolyte.

This statement is also true. The key characteristic of the impurities that form anode mud is their inability to dissolve in the electrolyte solution. If they were soluble, they would either remain in the electrolyte solution or potentially deposit onto the cathode, which would defeat the purpose of purification.

Explanation: Why Impurities Settle

The reason why insoluble impurities settle at the bottom of the anode is directly linked to their chemical property: they do not dissolve in the electrolyte.

Consider the process:

• The impure anode contains the desired metal along with impurities.
• When current is applied, the desired metal atoms at the anode lose electrons (get oxidized) and become ions, dissolving into the electrolyte (e.g., $Cu \to Cu^{2+} + 2e^-$).
• Impurities like gold, silver, platinum (less reactive metals) or other non-reactive materials do not get oxidized easily and thus do not form ions that dissolve in the electrolyte.
• As the main anode material dissolves, these unreacted, insoluble impurity particles are left behind and gravity causes them to fall to the bottom.

Therefore, the insolubility of these impurities (Reason R) is the direct cause of them settling down at the bottom of the anode (Assertion A).

Conclusion: Statement Validity and Relation

Both Statement (A) and Statement (R) are correct facts about electrolytic refining. Crucially, Statement (R) explains the underlying reason why Statement (A) happens. The impurities settle *because* they are insoluble in the electrolyte.