In the electrolytic refining of silver:

the anode is impure silver, cathode is pure silver

The correct answer is option 3. the anode is impure silver, cathode is pure silver.

In electrolytic refining of silver, the goal is to purify silver from an impure source. Here is a detailed explanation of the process and why the correct configuration is:

Process of Electrolytic Refining

Electrolytic Cell Setup:

Anode: This is the electrode where oxidation (loss of electrons) occurs. In the case of silver refining, the anode is made of impure silver. This means that the silver used at the anode contains both silver and other impurities.

Cathode: This is the electrode where reduction (gain of electrons) occurs. For refining silver, the cathode is made of pure silver. The pure silver cathode is where silver ions from the solution will be deposited.

Electrolyte Solution:

The electrolyte typically contains a silver salt, such as silver nitrate (AgNO₃), dissolved in water. The electrolyte provides a source of silver ions (Ag⁺) that migrate through the solution during the process.

Electrolytic Refining Steps

Oxidation at the Anode:

At the impure silver anode, silver atoms (Ag) lose electrons and become silver ions (Ag⁺) that dissolve into the electrolyte solution. The impurities present in the anode either remain at the anode or form insoluble compounds that do not dissolve into the solution.

\(\text{Ag (s)} \rightarrow \text{Ag}^+ \text{(aq)} + \text{e}^-\)

Migration of Silver Ions:

The silver ions (Ag⁺) in the electrolyte solution migrate towards the cathode under the influence of an electric current.

Reduction at the Cathode:

At the pure silver cathode, silver ions (Ag⁺) gain electrons and are reduced to solid silver (Ag) which gets deposited onto the cathode. This results in the gradual buildup of pure silver on the cathode.

\(\text{Ag}^+ \text{(aq)} + \text{e}^- \rightarrow \text{Ag (s)}\)

Why the Correct Configuration is (Anode: Impure Silver, Cathode: Pure Silver)

Impure Silver at the Anode:

The impure silver at the anode dissolves into the electrolyte, supplying silver ions to the solution. The presence of impurities in the anode does not affect the process as these impurities are either left behind or precipitate out of solution.

Pure Silver at the Cathode:

The pure silver cathode serves as the substrate where the pure silver ions are deposited. This ensures that the silver deposited on the cathode is of high purity.

Incorrect Options Explained

1. the anode is pure silver, cathode is impure silver:

If the anode were pure silver, there would be no source of silver ions from an impure source, and impurities would not be removed effectively. The cathode should always be pure silver to collect and form pure silver.

2. the anode is platinum, cathode is pure silver:

Platinum is not used as an anode material for refining silver. It is often used in electrolysis where no specific dissolution of the anode material is involved.

4. Both anode and cathode are platinum:  

Using platinum for both electrodes does not facilitate the purification of silver, as platinum does not participate in the dissolution or deposition of silver ions.

In summary, the correct configuration for electrolytic refining of silver is: 3. The anode is impure silver, the cathode is pure silver

This setup ensures that the silver is purified effectively by dissolving impure silver and depositing pure silver on the cathode.