The following sketch is of a voltaic cell consisting of two...

The following sketch is of a voltaic cell consisting of two standard electrodes for two metals, $M$ and $N$ : $$\begin{array}{ll} \mathrm{M}^{2+}(\mathrm{aq})+z \mathrm{e}^{-} \longrightarrow \mathrm{M}(\mathrm{s}) & E_{\mathrm{M}^{2+} / \mathrm{M}}^{\circ} \\ \mathrm{N}^{2+}(\mathrm{aq})+z \mathrm{e}^{-} \longrightarrow \mathrm{N}(\mathrm{s}) & E_{\mathrm{N}^{2+} / \mathrm{N}}^{\circ} \end{array}$$ Use the standard reduction potentials of these halfreactions to answer the questions that follow: $$\begin{array}{c} \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ag}(\mathrm{s}) \\ \mathrm{Zn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Zn}(\mathrm{s}) \\ \mathrm{Cu}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Cu}(\mathrm{s}) \\ \mathrm{A} 1^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s}) \end{array}$$ (a) Determine which pair of these half-cell reactions leads to a cell reaction with the largest positive cell potential, and calculate its value. Which couple is at the anode and which at the cathode? (b) Determine which pair of these half-cell reactions leads to the cell with the smallest positive cell potential, and calculate its value. Which couple is at the anode and which is at the cathode?

The following sketch is of a voltaic cell consisting of two standard electrodes for two metals, $M$ and $N$ :
$$\begin{array}{ll}
\mathrm{M}^{2+}(\mathrm{aq})+z \mathrm{e}^{-} \longrightarrow \mathrm{M}(\mathrm{s}) & E_{\mathrm{M}^{2+} / \mathrm{M}}^{\circ} \\
\mathrm{N}^{2+}(\mathrm{aq})+z \mathrm{e}^{-} \longrightarrow \mathrm{N}(\mathrm{s}) & E_{\mathrm{N}^{2+} / \mathrm{N}}^{\circ}
\end{array}$$
Use the standard reduction potentials of these halfreactions to answer the questions that follow:
$$\begin{array}{c}
\mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} \longrightarrow \mathrm{Ag}(\mathrm{s}) \\
\mathrm{Zn}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Zn}(\mathrm{s}) \\
\mathrm{Cu}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \longrightarrow \mathrm{Cu}(\mathrm{s}) \\
\mathrm{A} 1^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s})
\end{array}$$
(a) Determine which pair of these half-cell reactions leads to a cell reaction with the largest positive cell potential, and calculate its value. Which couple is at the anode and which at the cathode?
(b) Determine which pair of these half-cell reactions leads to the cell with the smallest positive cell potential, and calculate its value. Which couple is at the anode and which is at the cathode?

Key Concepts

Electrode Pair Selection for Maximum and Minimum Cell Potential

Selecting the appropriate electrode pairs involves comparing the standard reduction potentials of the available half-reactions. For the largest positive cell potential, one should pair the half-reaction with the highest standard reduction potential (acting as the cathode) with the one that has the lowest standard reduction potential (serving as the anode), thereby maximizing the difference (E_cathode ? E_anode). Conversely, to achieve the smallest positive cell potential, the half-reaction with a slightly higher reduction potential is paired with another reaction with a marginally lower reduction potential, minimizing this difference while still maintaining a spontaneous overall reaction.

Anode and Cathode Processes

In any electrochemical cell, the cathode is the electrode where reduction (gain of electrons) occurs, while the anode is where oxidation (loss of electrons) occurs. The identification of these processes is based on the relative standard reduction potentials of the half-reactions: the half-cell with the higher reduction potential typically acts as the cathode, and the one with the lower reduction potential serves as the anode.

Cell Potential Calculation

The overall cell potential (electromotive force) of a voltaic cell is determined by subtracting the standard reduction potential of the anode (site of oxidation) from that of the cathode (site of reduction). This is expressed mathematically as E_cell = E_cathode ? E_anode. A positive cell potential indicates a spontaneous reaction under standard conditions.

Standard Reduction Potential

The standard reduction potential is a measure of the tendency of a chemical species to gain electrons and be reduced under standard conditions (1 M concentration, 1 atm pressure, and 25°C). These potentials, typically listed in tables, help predict the direction of electron flow when different half-reactions are combined in an electrochemical cell.

Voltaic (Galvanic) Cell

A voltaic cell is an electrochemical cell that converts chemical energy into electrical energy through a spontaneous redox reaction. In such cells, two half-cell reactions (one oxidation and one reduction) occur in separate compartments and are connected by an external circuit and a salt bridge, enabling the flow of electrons between the electrodes.

Transcript

Please give Ace some feedback