Tarnished silver contains Ag2S. The tarnish can be removed by placing silverware in an aluminum pan containing an inert electrolyte soln, such as NaCL. Explain the electrochemical principle for this procedure, [The standard reduction potential for the half-cell reaction Ag2S(s)+2e-¡æ2Ag(s)+s^2-(aq) is .0.72V]
I can't read your equation. The idea here is that Al goes into solution and Ag^+ comes out of solution. You can write the two half cells.
Al ==> Al^+3 + 3e Eo = ??
Ag^+ +e ==> Ag(s) Eo = ??
Then balance the equations and add the two Eo values.
The electrochemical principle behind removing tarnish from silverware using aluminum and a salt solution is based on a redox reaction. Redox stands for reduction-oxidation, which involves the transfer of electrons between species.
In this case, the tarnish on silverware is caused by the presence of silver sulfide (Ag2S). To remove the tarnish, silver sulfide needs to be converted back into elemental silver (Ag). This conversion is achieved through a reduction reaction.
When silver sulfide (Ag2S) is in contact with aluminum (Al) in the presence of an electrolyte solution like sodium chloride (NaCl), the following reaction occurs:
2Al(s) + 3Ag2S(s) → 6Ag(s) + Al2S3(s)
In this reaction, aluminum (Al) acts as the reducing agent, meaning it loses electrons and undergoes oxidation. The silver sulfide (Ag2S) is reduced, meaning it gains electrons and forms elemental silver (Ag).
The aluminum metal provides a source of electrons through its oxidation process, while the silver sulfide acts as the oxidizing agent. The electrolyte solution, such as sodium chloride (NaCl), serves as a medium for conducting electricity by providing ions that can carry electric charge.
Essentially, the aluminum donates electrons, which reduces the silver sulfide to elemental silver, removing the tarnish. The reaction takes place due to the difference in standard reduction potentials between the two species involved.
The electrochemical principle behind the procedure of removing tarnish from silverware by placing it in an aluminum pan containing an inert electrolyte solution, such as NaCl, is called galvanic or electrochemical corrosion. This process takes advantage of the difference in reduction potentials between the silver sulfide (Ag2S) on the silverware and the aluminum (Al) in the pan.
The standard reduction potential of the half-cell reaction for the reduction of silver sulfide can be represented as follows:
Ag2S(s) + 2e- ⇌ 2Ag(s) + S2-(aq) E° = 0.72V
According to the electrochemical series, elements with higher reduction potentials are more easily reduced or undergo reduction reactions. In this case, the standard reduction potential of silver sulfide (Ag2S) is higher than that of aluminum (Al). Therefore, when the tarnished silverware is immersed in the electrolyte solution, a galvanic cell is set up.
The aluminum pan serves as the anode, where oxidation occurs, and the silverware acts as the cathode, where reduction takes place. During this process, aluminum atoms at the surface of the pan are oxidized, losing electrons to form aluminum cations (Al3+):
2Al(s) → 2Al3+(aq) + 6e-
Simultaneously, silver sulfide on the surface of the silverware is reduced by gaining electrons, transforming into silver metal (Ag):
Ag2S(s) + 2e- → 2Ag(s) + S2-(aq)
As the reaction progresses, the reduction of silver sulfide causes the tarnish to be removed from the silverware. The electrons released during the oxidation of aluminum at the anode flow through the wire connecting the two electrodes (silverware and aluminum pan), creating an electric current to complete the circuit.
Overall, this galvanic cell setup allows for the migration of silver ions from the tarnished silverware to the aluminum pan, resulting in the removal of the tarnish and the restoration of the silver's original appearance.