A mixture of copper and gold metals that is subjected to electrorefining contains tellurium as an impurity. The standard reduction potential between tellurium and its lowest common oxidation state, \(\mathrm{Te}^{4+}\), is $$ \mathrm{Te}^{4+}(a q)+4 \mathrm{e}^{-} \longrightarrow \mathrm{Te}(s) \quad E_{\mathrm{red}}^{\circ}=0.57 \mathrm{~V} $$ Given this information, describe the probable fate of tellurium impurities during electrorefining. Do the impurities fall to the bottom of the refining bath, unchanged, as copper is oxidized, or do they go into solution as ions? If they go into solution, do they plate out on the cathode?

Electrorefining is a process in which an impure metal is purified through the use of an electrolytic cell. In this case, a copper-gold mixture with tellurium impurities is being refined. When a voltage is applied, the impure metal reacts at the anode, and the pure metal deposits at the cathode. Impurities can either settle to the bottom as slag or enter the solution, depending on their properties.

We know the following information from the problem statement: - The standard reduction potential for tellurium, \(E_{\mathrm{red}}^\circ(\mathrm{Te}^{4+}/\mathrm{Te})\), is 0.57 V. - We are trying to determine the fate of tellurium impurities during electrorefining.

To determine the probable fate of tellurium impurities, we need to compare its standard reduction potential with that of copper. The standard reduction potentials for copper and gold are as follows: - Copper: \(E_{\mathrm{red}}^\circ(\mathrm{Cu}^{2+}/\mathrm{Cu}) = +0.337 \mathrm{~V}\) - Gold: \(E_{\mathrm{red}}^\circ(\mathrm{Au}^{3+}/\mathrm{Au}) = +1.498 \mathrm{~V}\) Since the standard reduction potential of tellurium is higher than that of copper but lower than gold, tellurium is more likely to be reduced than copper, but not as likely as gold.

We now consider the three possible scenarios: 1. Impurities fall to the bottom, unchanged: This situation would occur if tellurium neither oxidizes nor reduces during the electrorefining process, which is unlikely given the provided reduction potential. 2. Impurities go into solution as ions: This happens if tellurium oxidizes more readily than copper. Comparing reduction potentials, we find that tellurium's potential is higher than copper's. Therefore, tellurium is more likely to be reduced than copper, implying that tellurium ions would enter the solution and not turn to slag. 3. Impurities plate out on the cathode: This situation can occur when a metal with a higher reduction potential than copper plates out on the cathode during the process. The reduction potential of tellurium is higher than copper but lower than gold, which means tellurium will have a tendency to plate out on the cathode along with gold but before copper. Based on the discussion above, the probable fate of tellurium impurities during electrorefining is to go into solution as \(\mathrm{Te}^{4+}\) ions and then plate out on the cathode.