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Chapter 20: Problem 31

(a) What is the definition of the volt? (b) Do all voltaic cells produce a positive cell potential?

Short Answer

Expert verified
(a) A volt (V) is the unit of electrical potential difference in the SI system, defined as the potential difference across which one joule of work must be done to move a positive charge of one coulomb from a lower to a higher potential point, represented mathematically as \( 1V = \frac{1J}{1C} \). (b) All voltaic cells produce a positive cell potential, as they rely on spontaneous redox reactions to generate electrical energy. If a cell produces a negative cell potential, it would be considered an electrolytic cell instead, requiring external energy to drive the non-spontaneous redox reaction.

Step by step solution

01

(a) Definition of a volt:

A volt (V) is the unit of electrical potential difference in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta. One volt is the electrical potential difference across which one joule of work must be done to move a positive charge of one coulomb from the lower potential point to the higher potential point. Mathematically, it can be expressed as: \( 1V = \frac{1J}{1C} \) where V represents the voltage in volts, J represents the work done in joules, and C represents the charge in coulombs.
02

(b) Positive cell potential in voltaic cells:

A voltaic cell is an electrochemical cell in which a spontaneous redox (reduction-oxidation) reaction occurs, producing electrical energy. The cell potential, also known as the electromotive force (EMF), is the measure of the driving force that pushes the electrons through the external circuit. In general, a positive cell potential indicates that the redox reaction is spontaneous, and the cell can generate electrical energy. A positive cell potential would mean that the electrons would flow from the anode (the place of oxidation) to the cathode (the place of reduction) in the external circuit. So, do all voltaic cells produce a positive cell potential? In short, yes. To classify as a voltaic cell, the redox reaction must be spontaneous, which results in a positive cell potential. If it generated a negative cell potential, the cell would not be considered a voltaic cell, and the reaction would not be spontaneous. Instead, it would be an electrolytic cell, which requires an external energy source to drive the non-spontaneous redox reaction.

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Most popular questions from this chapter

Complete and balance the following equations, and identify the oxidizing and reducing agents: $$ \begin{array}{l}{\text { (a) } \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{I}(a q) \longrightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{IO}_{3}^{-}(a q)} \\ \quad {\text { (acidic solution) }} \\ {\text { (b) } \mathrm{MnO}_{4}^{-}(a q)+\mathrm{CH}_{3} \mathrm{OH}(a q) \longrightarrow \mathrm{Mn}^{2+}(a q)+} \\ \quad {\mathrm{HCOOH}(a q) \text { (acidic solution) }}\end{array} \\ {\text {(c) } \mathrm{I}_{2}(s)+\mathrm{OCl}^{-}(a q) \longrightarrow \mathrm{IO}_{3}^{-}(a q)+\mathrm{Cl}^{-}(a q)} \\ {\text { (acidic solution) }} \\ {\text { (d) } \mathrm{As}_{2} \mathrm{O}_{3}(s)+\mathrm{NO}_{3}(a q) \longrightarrow \mathrm{H}_{3} \mathrm{AsO}_{4}(a q)+\mathrm{N}_{2} \mathrm{O}_{3}(a q)} \\ {(\text { acidic solution })} \\ {\text { (e) } \operatorname{MnO}_{4}^{-}(a q)+\operatorname{Br}^{-}(a q) \longrightarrow \mathrm{MnO}_{2}(s)+\mathrm{BrO}_{3}^{-}(a q)} \\ {\text { (basic solution) }} \\ {\text { (f) } \mathrm{Pb}(\mathrm{OH})_{4}^{2-}(a q)+\mathrm{ClO}^{-}(a q) \longrightarrow \mathrm{PbO}_{2}(s)+\mathrm{Cl}^{-}(a q)} \\ {\text { (basic solution) }} $$

Indicate whether each statement is true or false: (a) The cathode is the electrode at which oxidation takes place. (b) A galvanic cell is another name for a voltaic cell. (c) Electrons flow spontaneously from anode to cathode in a voltaic cell.

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?

A voltaic cell is constructed with two \(\mathrm{Zn}^{2+}-\) Zn electrodes. The two half-cells have \(\left[\mathrm{Zn}^{2+}\right]=1.8 M\) and \(\left[\mathrm{Zn}^{2+}\right]=1.00 \times 10^{-2} M,\) respectively. (a) Which electrode is the anode of the cell? (b) What is the standard emf of the cell? (c) What is the cell emf for the concentrations given? (d) For each electrode, predict whether \(\left[\mathrm{Zn}^{2+}\right]\) will increase, decrease, or stay the same as the cell operates.

Gold exists in two common positive oxidation states, \(+1\) and \(+3 .\) The standard reduction potentials for these oxidation states are $$ \begin{array}{ll}{\mathrm{Au}^{+}(a q)+\mathrm{e}^{-}} \quad {\longrightarrow \mathrm{Au}(s) \quad E_{\mathrm{red}}^{\circ}=+1.69 \mathrm{V}} \\\ {\mathrm{Au}^{3+}(a q)+3 \mathrm{e}^{-} \longrightarrow \mathrm{Au}(s)} \quad {E_{\mathrm{red}}^{\circ}=+1.50 \mathrm{V}}\end{array} $$ (a) Can you use these data to explain why gold does not tarnish in the air? ( b) Suggest several substances that should be strong enough oxidizing agents to oxidize gold metal. (c) Miners obtain gold by soaking gold-containing ores in an aqueous solution of sodium cyanide. A very soluble complex ion of gold forms in the aqueous solution because of the redox reaction $$ \begin{array}{rl}{4 \mathrm{Au}(s)+8 \mathrm{NaCN}(a q)+2} & {\mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(g)} \\ {\longrightarrow} & {4 \mathrm{Na}\left[\mathrm{Au}(\mathrm{CN})_{2}\right](a q)+4 \mathrm{NaOH}(a q)}\end{array} $$ What is being oxidized, and what is being reduced in this reaction? (d) Gold miners then react the basic aqueous product solution from part (c) with Zn dust to get gold metal. Write a balanced redox reaction for this process. What is being oxidized, and what is being reduced?
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