A voltaic cell is constructed with an \(\mathrm{Sn} / \mathrm{Sn}^{2+}\) half- cell and a \(\mathrm{Zn} / \mathrm{Zn}^{2+}\) half-cell. The zinc electrode is negative. (a) Write balanced half-reactions and the overall cell reaction. (b) Diagram the cell, labeling electrodes with their charges and showing the directions of electron flow in the circuit and of cation and anion flow in the salt bridge.

Oxidation-reduction (redox) reactions are chemical reactions that involve the transfer of electrons between two substances. One substance loses electrons (oxidation) and another gains electrons (reduction).

In the context of a voltaic cell, like the one given in the exercise, zinc is oxidized, meaning it loses electrons, while tin is reduced, meaning it gains electrons. This can be seen in the half-reactions:

- **Oxidation**: \( \text{Zn (s)} \rightarrow \text{Zn}^{2+} \text{(aq)} + 2e^{-} \)
- **Reduction**: \( \text{Sn}^{2+} \text{(aq)} + 2e^{-} \rightarrow \text{Sn (s)} \)

Together, these half-reactions represent the overall redox process in the cell, resulting in the overall cell reaction: \( \text{Zn (s)} + \text{Sn}^{2+} \text{(aq)} \rightarrow \text{Zn}^{2+} \text{(aq)} + \text{Sn (s)} \). This exchange of electrons is what generates electrical energy in a voltaic cell.

Electrochemical cells are devices that convert chemical energy into electrical energy through redox reactions. There are two main types: voltaic (or galvanic) cells and electrolytic cells.

Voltaic cells, like the one in the exercise, generate spontaneous electrical energy from redox reactions between two different metals or metal compounds. In our example, zinc and tin form the two half-cells of the voltaic cell.

- **Anode**: The electrode where oxidation occurs. It is negative in a voltaic cell. Here, zinc (Zn) is the anode.
- **Cathode**: The electrode where reduction occurs. It is positive in a voltaic cell. Here, tin (Sn) is the cathode.

The flow of electrons from anode to cathode through an external circuit generates electrical energy. The movement of cations towards the cathode and anions towards the anode through a salt bridge maintains charge balance and completes the circuit.

A cell diagram is a shorthand representation of an electrochemical cell, showing the arrangement of the different components and their interactions. For the given voltaic cell involving zinc and tin, the cell diagram would look like this:

** Zn (s) | Zn^{2+} (aq) || Sn^{2+} (aq) | Sn (s) **

Here is how the cell diagram is structured:
- The single vertical line (|) represents a phase boundary, such as between a solid electrode and an aqueous solution.
- The double vertical line (||) represents the salt bridge between the two half-cells.

In the cell, electrons flow from the zinc electrode (anode) to the tin electrode (cathode), while the salt bridge allows ions to flow to balance the charges. This process can be visualized in a two-container setup, labeled with:
- The zinc electrode (anode) on the left, labeled negative, with Zn^{2+} ions flowing into the solution as zinc is oxidized.
- The tin electrode (cathode) on the right, labeled positive, with Sn^{2+} ions being reduced and depositing tin metal.
- The external circuit connecting the electrodes and completing the electrical flow path.
- The salt bridge, allowing anionic and cationic flow to maintain electrical neutrality.