Explain why a solution of \(\mathrm{HCl}\) in benzene does not conduct electricity but in water it does.

Ionic dissociation is crucial for understanding why certain substances conduct electricity when dissolved in a solvent, while others do not.

When a compound like HCl is dissolved in a solvent, its molecules may separate into positively charged cations and negatively charged anions. This process is known as ionic dissociation. These ions are essential as they carry the electric charge through the solution, enabling electrical conductivity. However, not all solvents promote ionic dissociation equally. Factors such as the solvent's molecular structure and its interactions with the solute play vital roles.

For instance, when HCl is dissolved in water, a polar solvent, the water molecules surround the HCl molecules. The slightly positive part of the water molecules attracts the Cl- ions, while the slightly negative part draws in the H+ ions. This electrostatic attraction is strong enough to separate the HCl into ions. Therefore, a solution's ability to conduct electricity is significantly influenced by the degree to which a solute undergoes ionic dissociation in a given solvent.

The distinction between polar and nonpolar solvents is a fundamental concept in understanding solubility and conductivity of solutions.

A polar solvent, like water, has molecules with a significant difference in charge distribution across its ends, which creates a dipole moment. This polarity allows it to dissolve ionic compounds and polar molecules effectively. The positive and negative ends of polar solvent molecules can interact with solutively charged ions, facilitating ionic dissociation.

On the other hand, nonpolar solvents such as benzene have molecules where the charge distribution is more uniform. Since there is no significant difference in the electric charge from one part of the molecule to another, nonpolar solvents are not adept at dissolving ionic compounds. They lack the ability to separate ions from an ionic lattice or prevent recombination of ions into neutral molecules. Consequently, a solution of HCl in benzene remains un-ionized, and hence incapable of conducting electricity due to the absence of ionic dissociation.

Mobile charge carriers are the ions or electrons that move through a solution or material, allowing it to conduct electricity. In the context of solutions, these carriers are typically ions that have resulted from the dissociation of an ionic solid or molecular compound.

The presence of mobile charge carriers is essential for electrical conductivity. In a solution where ionic dissociation occurs, such as HCl in water, the resulting H+ and Cl- ions serve as carriers for electrical charge. As these ions are free to move throughout the solution, they allow an electrical current to pass when a voltage is applied. The better the mobility of these charge carriers and the higher their concentration, the better the conductivity of the solution.

In contrast, in a non-conducting solution, such as HCl in benzene, the lack of ionic dissociation means no charge carriers are present to move the charge. Without these carriers, no current can flow, and the solution is effectively an insulator. Understanding the nature and availability of these mobile charge carriers is essential for grasping why some solutions conduct electricity and others do not.