Problem 109 - General Chemistry: Principles and Modern Applications

Question

Briefly describe each of the following ideas, methods, or devices: (a) salt bridge; (b) standard hydrogen electrode (SHE); (c) cathodic protection; (d) fuel cell.

Step-by-Step Solution

Answer

A salt bridge is a laboratory device maintaining electrical neutrality in a galvanic cell. The standard hydrogen electrode (SHE) is a redox electrode used as a reference for the determination of electrode potentials. Cathodic protection is a method used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A fuel cell is a device converting chemical potential energy into electrical energy, typically using hydrogen fuel and oxygen.

Step 1: Describing Salt Bridge

A salt bridge, in electrochemistry, is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (a type of battery), a type of electrochemical cell. It maintains electrical neutrality within the internal circuit, preventing the cell from rapidly running its reaction to equilibrium.

Step 2: Describing Standard Hydrogen Electrode (SHE)

The Standard Hydrogen Electrode (SHE), sometimes also called normal hydrogen electrode (NHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. It is usually used as a reference electrode for the determination of electrode potentials of other half-cells.

Step 3: Describing Cathodic Protection

Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. It is a method used to protect an object from corrosion by connecting it to another, more easily corroded 'sacrificial metal' to act as the anode.

Step 4: Describing Fuel Cell

A fuel cell is a device that converts chemical potential energy (energy stored in molecular bonds) into electrical energy. A typical fuel cell involves hydrogen fuel and oxygen from the air to run a reaction that produces electricity, with water and heat as the only byproducts.

Key Concepts

Salt Bridge

In the realm of electrochemistry, a salt bridge is an essential component that serves as a stabilizing link between two half-cells in a galvanic cell. Its role is to maintain electrical neutrality by allowing ions to flow between the separate compartments containing the oxidation and reduction reactions. Without a salt bridge, the build-up of charge would stop the electrochemical reactions, halting the production of electrical current.

The typical salt bridge is filled with a gel containing a salt solution, such as potassium chloride or sodium sulfate, which does not react with the substances in either cell. The ions move from the bridge into the half-cells, completing the electrical circuit and enabling the cell to continue operating efficiently. This process ensures the steady production of current and prevents the reactions from reaching their equilibrium state too quickly.

Standard Hydrogen Electrode (SHE)

The Standard Hydrogen Electrode, commonly abbreviated as SHE, is a universal reference point in electrochemistry. This electrode compares the potential of other electrodes and electrochemical cells. It consists of a platinum electrode in contact with a solution of H⁺ ions at a concentration of 1 mole per liter and bathed in hydrogen gas at a pressure of 1 atmosphere.

The SHE is assigned an arbitrary potential of 0 volts, and it establishes a consistent reference for measuring and comparing the electrode potentials of different half-cells. This hydrogen electrode is paramount when tabulating standard electrode potentials, which are crucial in predicting the direction of redox reactions and the voltage output of galvanic cells.

Cathodic Protection

Cathodic protection (CP) is a technique strategically employed to guard metals against corrosion, a process that can be detrimental to the integrity of metal structures. The principle behind CP is making the metal to be protected serve as a cathode of an electrochemical cell. By doing so, the oxidation reaction, which leads to corrosion, is suppressed, as the protected metal is prevented from losing electrons.

There are two prominent methods of cathodic protection: the sacrificial anode method and the impressed current method. In the sacrificial anode technique, the protected metal is connected to a more reactive metal, like zinc or magnesium. These anodes willingly corrode (oxidize) in place of the protected structure. In the impressed current method, an external current source sends electrons to the protected metal to offset corrosive processes. This CP approach is often used for pipelines, ship hulls, and other substantial structures.

Fuel Cell

A fuel cell, often seen as the beacon of green energy, transforms chemical energy into electrical energy through a reaction not too dissimilar from combustion but without burning. It uses hydrogen as its primary fuel, which reacts with oxygen from the air to create electricity. This process is marvelled for its cleanliness, as it emits only water and heat as byproducts, making no room for pollutants typical of fossil fuel combustion.

Fuel cells consist of an anode, cathode and an electrolyte that allows ions, but not electrons, to cross. At the anode, hydrogen molecules are split into protons and electrons. The electrons generate electricity as they flow through an external circuit to the cathode. Meanwhile, the protons migrate through the electrolyte to combine with oxygen at the cathode, forming water. Fuel cells are lauded for their applications in various sectors, including transport and stationary power generation, providing a sustainable and efficient energy solution.