International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What happens to the HCl molecule when dissolved in polar solvents?

1. It remains intact

2. It dissociates into ions

3. It evaporates

4. It forms a gas

The correct answer is: It dissociates into ions

When hydrochloric acid (HCl) is dissolved in polar solvents, such as water, it dissociates into ions. This process occurs because polar solvents have a significant dipole moment that can stabilize ions, allowing the H^+ (hydronium ion) and Cl^- (chloride ion) to separate from each other. The polar nature of the solvent facilitates the breaking of the H-Cl bond as the positive end of the water molecules attracts the Cl^- ions and the negative end attracts the H^+ ions. This dissociation is fundamental to the properties of strong acids, like HCl, which fully ionize in solution. The presence of these ions contributes to the solution's conductivity and acidity. In contrast, the other options do not accurately describe the behavior of HCl in a polar solvent. For example, it does not remain intact, evaporate, or form gas under typical conditions of dissolution in a polar solvent. These alternative scenarios do not apply directly to the process of ionization that characterizes the behavior of HCl in such environments.