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Chapter 19: Problem 41

Tarnished silver contains \(\mathrm{Ag}_{2} \mathrm{~S}\). The tarnish can be removed by placing silverware in an aluminum pan containing an inert electrolyte solution, such as \(\mathrm{NaCl}\). Explain the electrochemical principle for this procedure. [The standard reduction potential for the half- cell reaction \(\mathrm{Ag}_{2} \mathrm{~S}(s)+2 e^{-} \rightarrow 2 \mathrm{Ag}(s)+\mathrm{S}^{2-}(a q)\) is \(-0.71 \mathrm{~V} .]\)

Short Answer

Expert verified
The cleaning of tarnished silverware in an aluminum pan with an electrolyte solution works on the principle of electrochemistry. The aluminum acts as a sacrificial anode, oxidizing to release electrons. These electrons reduce the tarnish (Ag2S) on the silverware back to silver metal, effectively cleaning it. The direction of electron flow is determined by the standard reduction potentials of the reactions involved.

Step by step solution

01

Identify the Redox Reactions

In the aluminium pan with a NaCl solution, two half-cell reactions are occurring. On the silverware (anode), a reduction reaction occurs: \[ \mathrm{Ag}_{2} \mathrm{~S}(s)+2 e^{-} \rightarrow 2 \mathrm{Ag}(s)+\mathrm{S}^{2-}(a q) \] Meanwhile, the aluminum acts as the cathode where an oxidation reaction takes place. This has to be determined first.
02

Determine the Half-cell Reaction for Aluminum

Knowing that aluminum is oxidized in this process, we can write the half-cell reaction for aluminum: \[ \mathrm{Al}(s) \rightarrow \mathrm{Al}^{3+}(a q)+3 e^{-} \]
03

Use the Electrochemical Series

The electrochemical series puts the electrode reactions in order of their standard electrode potentials. The series shows that aluminum has a more negative standard electrode potential than silver and thus, is more likely to lose electrons (oxidize).
04

Explain the Cleaning Process

The electrolyte solution enables ions to travel. As a result, the Al is oxidized, allowing electrons to be released and move to the Ag2S on the silverware. Here, the electrons are gained by the Ag2S, reducing it back to silver metal and thus, cleaning the tarnish.
05

Importance of Standard Reduction Potential

The negative potential given (-0.71V for the reduction of Ag2S to Ag) indicates that the reaction is non-spontaneous and requires an external source of electrons. Here, the aluminium provides the necessary electrons to reduce Ag2S on the silverware.

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Most popular questions from this chapter

Write the Nernst equation for the following processes at some temperature \(T\) : (a) \(\mathrm{Mg}(s)+\mathrm{Sn}^{2+}(a q) \longrightarrow \mathrm{Mg}^{2+}(a q)+\operatorname{Sn}(s)\) (b) \(2 \mathrm{Cr}(s)+3 \mathrm{~Pb}^{2+}(a q) \longrightarrow 2 \mathrm{Cr}^{3+}(a q)+3 \mathrm{~Pb}(s)\)

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