Electrolytes are substances that gain the capacity to conduct electricity when dissolved in water or melted. This electrical conductivity arises from the presence of mobile, charged particles known as ions within the solution. The ability of a dissolved substance to generate these ions determines its classification in chemistry.
Understanding Electrolytes and Dissociation
An electrolyte’s ability to conduct an electric current depends on a process called dissociation. Dissociation is the physical separation of an ionic compound into its constituent positive ions, or cations, and negative ions, or anions, when surrounded by polar water molecules. Water, being a polar solvent, is highly effective at overcoming the strong electrostatic forces that hold the ions together in the solid crystal structure.
The extent of this separation determines the substance’s categorization as either a strong or a weak electrolyte. Strong electrolytes undergo complete dissociation into ions when dissolved in water. This high concentration of mobile ions means the resulting solution is an excellent conductor of electricity. Conversely, weak electrolytes only dissociate partially, leaving most of the original substance in its molecular form, which results in poor electrical conductivity.
The Nature of Sodium Carbonate
Sodium carbonate (\(\text{Na}_2\text{CO}_3\)) is an inorganic salt, commonly known as soda ash or washing soda. As a compound formed from the metal sodium (\(\text{Na}\)) and the polyatomic carbonate ion (\(\text{CO}_3^{2-}\)), it is classified as an ionic substance. The crystal structure of solid sodium carbonate is held together by strong ionic bonds between the sodium cations and the carbonate anions.
When sodium carbonate is introduced to water, it is highly soluble, meaning the polar water molecules readily break these ionic bonds. The water molecules surround the individual ions, a process known as solvation, which effectively separates the ions and prevents them from re-associating. Chemically, this salt is derived from the reaction between a strong base, sodium hydroxide (\(\text{NaOH}\)), and a weak acid, carbonic acid (\(\text{H}_2\text{CO}_3\)).
Why Sodium Carbonate is a Strong Electrolyte
Sodium carbonate is classified as a strong electrolyte because of its behavior in aqueous solution. The rule in chemistry is that all soluble ionic salts, including \(\text{Na}_2\text{CO}_3\), dissociate completely upon dissolving. This complete separation ensures the maximum possible concentration of charged particles is available to facilitate the flow of electric current.
When one unit of solid sodium carbonate dissolves, it yields three separate ions in the solution. The compound breaks apart into two sodium ions (\(2\text{Na}^+\)) and one carbonate ion (\(\text{CO}_3^{2-}\)), as shown in the dissociation equation: \(\text{Na}_2\text{CO}_3(\text{aq}) \rightarrow 2\text{Na}^+(\text{aq}) + \text{CO}_3^{2-}(\text{aq})\). Because the dissolved salt separates completely, the solution contains a dense population of mobile ions. This high concentration allows the solution to conduct electricity effectively, confirming its classification as a strong electrolyte.
Strong Electrolyte Behavior Versus Solution pH
A common point of confusion arises because the classification of a substance as a strong electrolyte is distinct from the resulting solution’s acidity or basicity, which is measured by pH. While \(\text{Na}_2\text{CO}_3\) is a strong electrolyte due to its complete dissociation, the solution it forms is notably basic. This basic nature is not a result of the initial dissociation, but a subsequent reaction involving one of the resulting ions.
The carbonate ion (\(\text{CO}_3^{2-}\)), which is the anion of the weak acid carbonic acid, acts as a weak base in water. This ion undergoes a reaction called hydrolysis, where it accepts a proton (\(\text{H}^+\)) from a water molecule. This process generates hydroxide ions (\(\text{OH}^-\)) according to the equation: \(\text{CO}_3^{2-} + \text{H}_2\text{O} \rightarrow \text{HCO}_3^- + \text{OH}^-\).
The production of these hydroxide ions raises the solution’s pH significantly above \(7\). Depending on the concentration, the pH of a sodium carbonate solution can range between \(11\) and \(12\), indicating a highly basic environment. Crucially, the basic nature of the solution does not diminish the fact that the original \(\text{Na}_2\text{CO}_3\) salt fully separated into ions, maintaining its classification as a strong electrolyte.