Question

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

Short answer

HCl conducts electricity in water due to ionization but not in benzene, as it stays undissociated.

Step-by-step solution

Understanding HCl in Different Solvents

Hydrochloric acid (HCl) behaves differently depending on the solvent it is in. In water, HCl dissociates into ions, but in benzene, it does not.

Observing HCl in Water

In water, HCl dissociates into hydrogen ions ( ext{H}^+) and chloride ions ( ext{Cl}^-). This process is called ionization: \[ ext{HCl (aq)} ightarrow ext{H}^+ (aq) + ext{Cl}^- (aq) \]These ions are charged particles that move freely in solution, conducting electricity.

Observing HCl in Benzene

Benzene is a non-polar solvent, which means it does not support the ionization of HCl. As a result, HCl remains in its molecular form (HCl) in benzene, without dissociating into ions.

Comparing the Effects

The presence of free-moving ions is essential for the conduction of electricity. Since HCl in water generates ions and HCl in benzene does not, electricity is conducted in the aqueous HCl solution but not in benzene.

Key concepts

Ionization

When hydrochloric acid (HCl) is dissolved in water, it undergoes a process called ionization. During ionization, HCl molecules dissociate into hydrogen ions (\( \text{H}^+ \)) and chloride ions (\( \text{Cl}^- \)). Water is a polar solvent, with a unique ability to stabilize these ions. This is why water facilitates the ionization of HCl effectively.In contrast, when HCl is mixed with benzene, a non-polar solvent, there is no ionization. Benzene does not have the ability to stabilize ions like water does. Therefore, HCl remains as intact molecules in benzene. This difference is crucial since the presence or absence of ions directly affects the solution's properties, such as electrical conductivity.

Conductivity

For a solution to conduct electricity, it must contain free-moving charged particles (ions). In the case of HCl in water, the ionization process produces hydrogen ions and chloride ions. These ions move freely in the aqueous solution, allowing electricity to pass through. However, in benzene, there is no ion formation because it doesn't support the ionization of HCl. Since there are no ions present to carry an electric current, a solution of HCl in benzene is unable to conduct electricity. Thus, understanding electrical conductivity in solutions requires an appreciation of how and why ions are formed.

Polar and Non-polar Solvents

The type of solvent plays a crucial role in determining whether a solute like HCl will ionize. Polar solvents, such as water, have molecules with positive and negative ends (dipoles) that can surround and stabilize ions formed from substances like HCl. Non-polar solvents, like benzene, lack this dipole characteristic. They have even distributions of electrical charge, meaning they cannot stabilize charged ions the way polar solvents do. Thus, polar solvents facilitate the ionization of solutes like HCl, while non-polar solvents do not. This fundamental difference in solvent properties explains why HCl behaves differently in water versus benzene.

Dissociation of Acids

Dissociation refers to the process where molecules split into smaller particles, usually ions. In the context of acids like HCl, dissociation is where the acid molecule separates into hydrogen ions and corresponding anions (chloride ions, in this case). This process is driven primarily by the nature of the solvent. A polar solvent encourages acid dissociation, while a non-polar solvent does not. Understanding dissociation is important because it is directly linked to the concept of acidity and conductivity in solutions. Without dissociation, an acid cannot exhibit its typical acidic or conductive properties, as seen with HCl in benzene.