Advanced Placement (AP) Chemistry Practice Exam

Which term describes the breaking up of ionic substances into its ions when dissolved in a solution?

1. Ionization

2. Dissociation

3. Solvation

4. Precipitation

The correct answer is: Dissociation

The process of breaking up ionic substances into their individual ions when they dissolve in a solution is referred to as dissociation. When ionic compounds, such as sodium chloride (NaCl), are mixed with water, the polar water molecules interact with the positive and negative ions of the compound. This interaction surrounds the ions and effectively pulls them apart into the solution. Each sodium ion (Na⁺) and chloride ion (Cl⁻) is then surrounded by water molecules, allowing them to disperse throughout the solvent. In contrast, the term ionization refers specifically to the process of forming ions from neutral atoms or molecules, often involving a chemical reaction or energy input. Solvation involves the interaction of solute particles with solvent molecules, which encompasses the process of dissociation but is broader and includes the stabilization of the ions as they enter the solution. Precipitation describes the process where soluble ions combine to form an insoluble solid that separates out of the solution, which is not relevant to the dissociation of ionic compounds. Thus, dissociation accurately captures the specific phenomenon of ionic compounds breaking apart into their respective ions upon dissolution.