Ammonium nitrate (\(\text{NH}_4\text{NO}_3\)) is a common compound used globally in various applications. It is widely recognized as a high-nitrogen fertilizer and is also a primary component in industrial explosive mixtures used in mining and construction. The interaction of this white crystalline salt with water raises a fundamental chemical question: does it qualify as a strong conductor of electricity in solution?
Understanding Electrolytes
An electrolyte is a substance that, when dissolved in water, produces ions and creates a solution capable of conducting an electric current. The water molecules effectively pull the constituent particles of the substance apart, allowing charged ions to move freely. The strength of an electrolyte is determined by the extent to which this separation, or dissociation, occurs in the aqueous solution.
Strong electrolytes are defined by their complete dissociation into ions, meaning virtually 100% of the dissolved substance forms charged particles. This high concentration of mobile ions makes the solution an excellent conductor of electricity. Examples of strong electrolytes include strong acids, strong bases, and most soluble salts.
In contrast, a weak electrolyte only partially dissociates or ionizes in water, typically ranging from 1% to 10%. This small number of resulting ions leads to a solution that conducts electricity poorly. Weak acids and weak bases, like acetic acid or ammonia, fall into this category. Non-electrolytes, such as sugar or ethanol, dissolve in water but do not form any ions, meaning the resulting solution does not conduct electricity at all.
Ammonium Nitrate as an Ionic Compound
Ammonium nitrate is unequivocally classified as a strong electrolyte. This classification is based on its chemical structure as an ionic compound, often referred to as a salt. The solid crystal lattice of \(\text{NH}_4\text{NO}_3\) is composed of two polyatomic ions: the positively charged ammonium cation (\(\text{NH}_4^+\)) and the negatively charged nitrate anion (\(\text{NO}_3^-\)).
A fundamental rule in chemistry is that soluble ionic compounds, or salts, are defined as strong electrolytes because they dissociate completely when dissolved in water. Ammonium nitrate has exceptionally high solubility, meaning it readily dissolves in water to a great extent.
Furthermore, the specific ions that make up the compound confirm its high solubility. Solubility rules state that all compounds containing the ammonium ion (\(\text{NH}_4^+\)) are soluble, without exception. Similarly, all compounds containing the nitrate ion (\(\text{NO}_3^-\)) are also soluble.
The Dissociation Process
The strong electrolyte nature of ammonium nitrate means its dissolution process involves a complete separation of its constituent ions. When the solid \(\text{NH}_4\text{NO}_3 (\text{s})\) is placed in water, the polar water molecules surround and pull apart the ions in the crystal lattice. This process is represented by a single arrow in the dissociation equation, which signifies the reaction goes entirely to completion: \(\text{NH}_4\text{NO}_3 (\text{s}) \rightarrow \text{NH}_4^+ (\text{aq}) + \text{NO}_3^- (\text{aq})\).
For every one mole of ammonium nitrate dissolved, one mole of ammonium ions and one mole of nitrate ions are produced, totaling two moles of ions. The complete and immediate generation of these mobile charged particles is what makes the resulting solution highly electrically conductive. The nitrate ion (\(\text{NO}_3^-\)) is derived from a strong acid, nitric acid, and does not undergo any further reaction with water molecules.
A nuance arises with the ammonium ion (\(\text{NH}_4^+\)), which is the conjugate acid of the weak base ammonia (\(\text{NH}_3\)). While the initial salt dissociation is 100%, the resulting \(\text{NH}_4^+\) ion can undergo a minor, secondary reaction with water called hydrolysis, acting as a very weak acid. However, this partial, secondary reaction does not diminish the initial complete dissociation of the salt itself.