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Ch.20 - Electrochemistry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.20 - ElectrochemistryProblem 96
Chapter 20, Problem 96

A mixture of copper and gold metals that is subjected toelectrorefining contains tellurium as an impurity. The standard reduction potential between tellurium and its lowestcommon oxidation state, Te4+, isTe4+1aq2 + 4 e- ¡ Te1s2 E°red = 0.57 VGiven this information, describe the probable fate of tellurium impurities during electrorefining. Do the impuritiesfall to the bottom of the refining bath, unchanged, as copper is oxidized, or do they go into solution as ions? If theygo into solution, do they plate out on the cathode?

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1
Identify the process of electrorefining, which involves the oxidation of the impure metal at the anode and the reduction of the pure metal at the cathode.
Consider the standard reduction potential of tellurium (Te) and compare it with the standard reduction potentials of copper (Cu) and gold (Au).
Recognize that during electrorefining, metals with higher reduction potentials than the metal being refined will remain in solution, while those with lower reduction potentials will not be reduced at the cathode.
Since the standard reduction potential of Te (0.57 V) is lower than that of Cu (0.34 V) and Au (1.50 V), Te is less likely to be reduced at the cathode compared to Cu and Au.
Conclude that tellurium impurities are likely to remain in solution as ions and do not plate out on the cathode, while copper and gold are selectively deposited.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrorefining Process

Electrorefining is a method used to purify metals by using electrolysis. In this process, an impure metal is made the anode, and pure metal is deposited at the cathode. The impurities, depending on their solubility and electrochemical properties, can either remain in the solution or settle at the bottom. Understanding this process is crucial to predicting the behavior of impurities like tellurium during electrorefining.
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Standard Reduction Potential

Standard reduction potential (E°red) is a measure of the tendency of a chemical species to gain electrons and be reduced. A higher E°red value indicates a greater likelihood of reduction occurring. In the context of tellurium, the given E°red of 0.57 V suggests that Te4+ ions can be reduced to solid tellurium, influencing whether tellurium will remain in solution or deposit on the cathode during electrorefining.
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Behavior of Impurities in Electrolytic Solutions

The behavior of impurities in electrolytic solutions is determined by their solubility and electrochemical properties. Impurities can either dissolve as ions or precipitate out depending on their reduction potentials and interactions with the electrolyte. In the case of tellurium, its ability to exist as Te4+ ions means it may go into solution during electrorefining, potentially leading to its deposition on the cathode if conditions favor its reduction.
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Related Practice
Textbook Question

A disproportionation reaction is an oxidation–reduction reaction in which the same substance is oxidized and reduced. Complete and balance the following disproportionation reactions:

(b) MnO42-(aq) → MnO4-(aq) + MnO2(s) (acidic solution)

Textbook Question

(a) Calculate the mass of Li formed by electrolysis of molten LiCl by a current of 7.5 × 104 A flowing for a period of 24 h. Assume the electrolytic cell is 85% efficient. (b) What is the minimum voltage required to drive the reaction?