An electrolyte is any substance that produces ions when dissolved in water, allowing the resulting solution to conduct an electric current. This movement of charged particles, or ions, is what facilitates the flow of electricity through the liquid. The strength of this electrical conductivity depends entirely on how efficiently the substance forms ions in the water. Determining if a substance is a strong electrolyte involves systematic identification based on a few distinct chemical categories.
What Makes an Electrolyte Strong
The difference between a strong electrolyte and a weaker one is the extent to which the substance dissociates or ionizes in an aqueous solution. A strong electrolyte is defined by its almost complete, 100% separation into constituent ions when dissolved in water. This high concentration of charged particles is what gives the solution a high electrical conductivity.
In contrast, a weak electrolyte, such as acetic acid, only partially dissociates, meaning most of the substance remains as intact molecules in the solution, limiting the number of ions available to carry a current. Non-electrolytes, like sugar or ethanol, do not dissociate into ions at all, and their solutions will not conduct electricity. The degree of ionization is the single defining factor for an electrolyte’s strength.
Identifying Strong Acids and Strong Bases
The first major category of strong electrolytes includes strong acids and strong bases. These compounds undergo complete ionization. Identifying these substances relies on a short, specific list, as any acid or base not on this list is considered weak.
The common strong acids include:
- Hydrochloric acid (HCl)
- Hydrobromic acid (HBr)
- Hydroiodic acid (HI)
- Nitric acid (HNO\(_{3}\))
- Perchloric acid (HClO\(_{4}\))
- Chloric acid (HClO\(_{3}\))
- Sulfuric acid (H\(_{2}\)SO\(_{4}\))
Only the first proton in sulfuric acid ionizes completely, but it is still categorized as a strong acid. The strong bases are the hydroxides of the Group 1 alkali metals and the heavier Group 2 alkaline earth metals.
The strong bases include:
- Lithium hydroxide (LiOH)
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Rubidium hydroxide (RbOH)
- Cesium hydroxide (CsOH)
The heavy Group 2 strong bases are calcium hydroxide (\(\text{Ca}(\text{OH})_{2}\)), strontium hydroxide (\(\text{Sr}(\text{OH})_{2}\)), and barium hydroxide (\(\text{Ba}(\text{OH})_{2}\)). If a compound is an acid or a base but does not appear on these specific lists, it is a weak electrolyte.
Identifying Soluble Ionic Compounds
The second large category of strong electrolytes is ionic compounds, formed from metal and nonmetal ions. The compounds are strong electrolytes if they are soluble in water, as they completely dissociate into constituent ions upon dissolving. Determining if an ionic compound is a strong electrolyte is a two-step process: first confirming it is ionic, and then consulting the solubility rules.
Certain ions always form soluble salts, which is the easiest way to identify a strong electrolyte. All compounds containing the following ions are universally soluble with no significant exceptions:
- Alkali metal ions (like \(\text{Na}^{+}\) or \(\text{K}^{+}\))
- Ammonium ion (\(\text{NH}_{4}^{+}\))
- Nitrate (\(\text{NO}_{3}^{-}\))
- Acetate (\(\text{CH}_{3}\text{CO}_{2}^{-}\))
- Perchlorate (\(\text{ClO}_{4}^{-}\))
These soluble compounds are strong electrolytes.
The next set of rules involves a few common exceptions that must be considered. Most salts containing chloride (\(\text{Cl}^{-}\)), bromide (\(\text{Br}^{-}\)), or iodide (\(\text{I}^{-}\)) are soluble, but they become insoluble—and thus not strong electrolytes—when paired with silver (\(\text{Ag}^{+}\)), lead (\(\text{Pb}^{2+}\)), or mercury(I) (\(\text{Hg}_{2}^{2+}\)). Most sulfate (\(\text{SO}_{4}^{2-}\)) salts are also soluble, with exceptions occurring when paired with barium (\(\text{Ba}^{2+}\)), lead (\(\text{Pb}^{2+}\)), and strontium (\(\text{Sr}^{2+}\)).