What must be present in an aqueous solution for it to conduct an electric current? What general classes of compounds form solutions that conduct?

When we talk about ions in a solution, we refer to charged particles that result from the dissolving of certain substances in water. These substances break down into their constituent ions, a process known as ionization. The movement of these ions allows the solution to conduct electricity. For instance, when table salt (sodium chloride) dissolves in water, it separates into sodium ions (Na⁺) and chloride ions (Cl^-).
Conductivity in an aqueous solution directly depends on the presence of these free-moving ions. The more ions present, the better the solution can conduct electricity. This is why pure water is a poor conductor; it has very few ions.
On the contrary, when substances like salts or acids dissolve in water, they release a considerable number of ions, enhancing the solution's ability to conduct electricity. Understanding the role of ions in solution is fundamental to grasping why certain solutions conduct electricity while others do not.

Ionic compounds are a key category of substances that contribute to solution conductivity. These compounds are formed from metals and nonmetals. In these compounds, atoms transfer electrons to form positive and negative ions, creating a lattice structure in the solid state.
When ionic compounds dissolve in water, they dissociate completely into their respective ions. For example, sodium chloride (NaCl) breaks down into sodium ions (Na⁺) and chloride ions (Cl^-). This release of ions into the solution is what makes it conductive.
Another example is potassium nitrate (KNO₃). When it dissolves, it separates into potassium ions (K⁺) and nitrate ions (NO₃^-). These free ions can move freely in the solution, allowing it to conduct an electric current.
It's important to understand that the ability of ionic compounds to form conductive solutions is due to their complete dissociation in water.

Acids and bases also play a significant role in the conductivity of aqueous solutions. Strong acids and bases ionize completely in water, releasing ions that enhance conductivity.
A strong acid, like hydrochloric acid (HCl), dissociates fully into hydrogen ions (H⁺) and chloride ions (Cl^-). These ions are free to move in the solution, making it highly conductive.
Similarly, a strong base, such as sodium hydroxide (NaOH), dissociates into sodium ions (Na⁺) and hydroxide ions (OH^-), contributing to the solution's conductivity.
It's worth mentioning that not all acids and bases are strong. Weak acids and bases do not dissociate completely in water, resulting in fewer ions and thus lower conductivity.
An example of a weak acid is acetic acid (CH₃COOH), which only partially dissociates in solution. Therefore, understanding the strength of acids and bases is crucial to predicting their effect on solution conductivity.