Hydrogen halides are covalent compounds but their aqueous solutions can conduct electric current. Explain.

Hydrogen halides, such as hydrochloric acid (HCl), hydrobromic acid (HBr), and hydrofluoric acid (HF), are indeed covalent compounds in their gaseous state. However, when these compounds dissolve in water, they exhibit the ability to conduct electric current. This phenomenon can be explained through the concepts of ionization and the nature of electrolytes.

The Nature of Hydrogen Halides

In their gaseous form, hydrogen halides consist of molecules made up of covalent bonds between hydrogen and halogen atoms. For example, in HCl, a hydrogen atom shares electrons with a chlorine atom, forming a covalent bond. This means that in the gas phase, hydrogen halides do not have free-moving charged particles, which are essential for conducting electricity.

Dissolution in Water

When hydrogen halides are introduced into water, they undergo a process called ionization. This is where the covalent bonds break, and the molecules dissociate into ions. For instance, when HCl dissolves in water, it ionizes as follows:

• HCl (aq) → H⁺ (aq) + Cl^- (aq)

This reaction shows that one molecule of hydrochloric acid produces one hydrogen ion (H⁺) and one chloride ion (Cl^-). The same process occurs for other hydrogen halides, resulting in the formation of their respective ions.

Conductivity of Aqueous Solutions

The key to understanding why aqueous solutions of hydrogen halides can conduct electricity lies in the presence of these ions. In an aqueous solution, the ions are free to move. When an electric field is applied, these charged particles migrate towards the electrodes: positive ions (cations) move towards the negative electrode (cathode), while negative ions (anions) move towards the positive electrode (anode). This movement of ions constitutes an electric current.

Electrolytes and Their Role

Hydrogen halides are classified as strong electrolytes because they completely ionize in water, producing a high concentration of ions. This is in contrast to weak electrolytes, which only partially ionize and produce fewer ions, resulting in lower conductivity. For example, acetic acid (CH₃COOH) is a weak electrolyte because it does not fully dissociate in solution.

Real-World Applications

The ability of hydrogen halides to conduct electricity in aqueous solutions has practical implications. For instance, hydrochloric acid is widely used in laboratories and industries, not only for its chemical properties but also for its ability to facilitate electrochemical reactions. Understanding the conductivity of these solutions is crucial in fields like electrochemistry, where the movement of ions is fundamental to processes such as electrolysis and battery operation.

In summary, while hydrogen halides are covalent compounds in their gaseous state, their ability to ionize in water transforms them into strong electrolytes, allowing their aqueous solutions to conduct electric current effectively. This interplay between molecular structure and ionic behavior is a fascinating aspect of chemistry that highlights the importance of understanding the properties of substances in different states.