Reactions in Aqueous Solutions: Solutions, Solubility, and Electrolytes

Reactions in Aqueous Solutions

Aqueous Solutions and Solubility

An aqueous solution is a homogeneous mixture of two or more substances where water acts as the solvent. The process of dissolving involves a solute (present in a smaller amount) and a solvent (present in the greatest amount), resulting in a uniform solution.

• Solute: The substance dissolved in the solvent; present in a smaller amount.

• Solvent: The substance that dissolves the solute; present in the greatest amount. Water is known as the universal solvent due to its ability to dissolve many substances.

• Solution: A homogeneous mixture of solute and solvent.

Example: Dissolving table salt (NaCl) in water forms a clear, uniform solution.

The Dissolution Process

When an ionic compound such as sodium chloride (NaCl) dissolves in water, the ions separate and disperse throughout the solution. Water molecules surround and stabilize the ions, preventing cations and anions from recombining.

• Solvation (Hydration): The process by which water molecules surround and interact with ions.

• Ion-Dipole Interactions: Water molecules, being polar, stabilize ions by orienting their partial charges toward the ions (oxygen toward cations, hydrogen toward anions).

Example: NaCl(s) dissolves to form Na+(aq) and Cl−(aq), each surrounded by water molecules.

Electrolyte and Nonelectrolyte Solutions

Substances dissolved in water can be classified based on their ability to conduct electricity:

• Electrolytes: Compounds whose aqueous solutions form ions that conduct electricity. These include most ionic compounds and some molecular compounds (acids).

• Nonelectrolytes: Compounds that do not dissociate into ions when dissolved in water and therefore do not conduct electricity. Most molecular compounds (except acids) are nonelectrolytes.

Example: Sodium chloride (NaCl) is a strong electrolyte. When dissolved:

$\mathrm{NaCl}(aq) \rightarrow \mathrm{Na}^+(aq) + \mathrm{Cl}^-(aq)$

This dissociation allows the solution to conduct electricity, as shown by a light bulb glowing when electrodes are placed in the solution.

Type of Compound	Behavior in Water	Electrical Conductivity
Ionic Compound (e.g., NaCl)	Dissociates into ions	Conducts electricity (electrolyte)
Molecular Compound (e.g., sugar)	Does not dissociate	Does not conduct electricity (nonelectrolyte)

Additional info: The images depict the molecular view of dissolution, showing water molecules surrounding ions and the resulting ability of the solution to conduct electricity.