Sections 8.8, 8.9, and 8.11 presented and applied three patterns that were used to write the chemical formulas and names of hydrohalogenated, "HX," and polyatomic, "HNPoly," Arrhenius acids and metal hydroxide, "M(OH)Y," Arrhenius bases, respectively. Recall that an Arrhenius acid is defined as a proton, H+1, donor in water, and an Arrhenius base is defined as a hydroxide ion, OH–1, donor in water. However, these patterns were developed solely based on the ion symbols, H+1 and OH–1, that are referenced in the definitions of Arrhenius acids and bases, respectively, and do not address the defined requirement that these ions be donated in water. Therefore, while the chemical formulas that were developed from these patterns contain the types of ions that must be present in Arrhenius acids and bases, since the dissociative behaviors of the corresponding molecules were not analyzed, these compounds cannot be definitively classified as Arrhenius acids or bases. Because the complete definitions of Arrhenius acids and bases were not utilized to develop the "HX," "HNPoly," and "M(OH)Y" patterns, applying these symbolisms to classify a particular chemical as an Arrhenius acid or an Arrhenius base is a "shortcut." Furthermore, since using a "shortcut" to analyze information occasionally generates misleading or erroneous results, as exemplified by the "Group A/B valence electron" and the "Reverse Criss-Cross Method" "shortcuts" that were presented in Sections 2.7 and 3.10, respectively, any acid/base classification that results from comparing these patterns to a particular chemical formula must be independently-verified through an alternative process, in order to be accepted by the scientific community.
Based on the criteria that are described in the previous paragraph, both the types of ions that are present in a compound and the dissociative behavior of that compound in an aqueous solution must be analyzed, in order to classify a substance as an Arrhenius acid or an Arrhenius base. Recall that the solution equations that were presented in Chapter 7 are, by definition, symbolic representations of the dissociative behaviors of solutes. Therefore, in order to definitively classify a chemical as an Arrhenius acid or an Arrhenius base through a scientifically-sound, verifiable process, the solution equation for a particular chemical must be written, and the generated symbolic information must then be compared to the chemical and behavioral criteria that are established in the definitions of Arrhenius acids and Arrhenius bases.
For example, use a solution equation to classify HNO3, which exhibits the characteristics of a strong electrolyte when dissolved in water, as an Arrhenius acid or an Arrhenius base.
Because the given chemical formula, HNO3, contains one hydrogen and a nitrate ion, NO3–1, which is a polyatomic anion, the corresponding molecule can be classified as a polyatomic, or "HNPoly," Arrhenius acid. However, because the "HNPoly" pattern is a "shortcut," in order to definitively classify HNO3 as an Arrhenius acid, a solution equation for this chemical must be written, and the generated symbolic information must be compared to the chemical and behavioral criteria that are established in the definition of an Arrhenius acid.
In order to apply the strong electrolyte solution equation pattern that was presented in Section 7.6, each substance that is referenced in the given statement must first be classified as a solute or a solvent. Because the indicator word "in" is present in the given statement, the chemical that is mentioned after this word, water, H2O, is the solvent in this solution, and the remaining substance, HNO3, is the solute, "by default."
A "forward," or left-to-right, arrow is utilized in the solution equation for a strong electrolyte, the chemical formula of the solvent, water, H2O, is written over this arrow, and the chemical formula of the solute, HNO3, is written on the left side of the arrow. Because a strong electrolyte completely dissociates into its constituent cations and anions as it dissolves, the ion symbol for each of these particles is written on the right side of the arrow. The anionic component of HNO3 is the nitrate ion, NO3–1, which is a polyatomic anion. The remaining element that is present in the given solute, hydrogen, H, does not typically ionize. However, because the given statement explicitly indicates that HNO3 exhibits the characteristics of a strong electrolyte, which must, by definition, dissociate into cations and anions during the solvation process, the hydrogen that is present in HNO3 must ionize to form a cation, H+1. Finally, in order to indicate that the cation and anion are unique particles, a plus sign is used to separate their symbols. The information that is described in this paragraph is reflected in the solution equation that is shown below.
Since the left and right sides of this solution equation contain equal amounts of hydrogen ions, H+1, and nitrate ions, NO3–1, the solution equation that is shown above is balanced and, therefore, is the chemically-correct representation of the dissociation of HNO3 in water.
Recall that an Arrhenius acid is defined as a proton, H+1, donor in water, and an Arrhenius base is defined as a hydroxide ion, OH–1, donor in water. Therefore, in order to be classified as an Arrhenius acid, both the types of ions that are present in the given solute, HNO3, and the dissociative behavior of HNO3in an aqueous solution must be analyzed.
Because an Arrhenius acid must be dissolved in an aqueous solution, water must be the solvent that is used to prepare an Arrhenius solution. As stated above, the chemical formula of the solvent must be written over the arrow in a solution equation. Therefore, because "H2O," the chemical formula of water, occupies this position in the solution equation that is shown above, the requirement that an Arrhenius acid be dissolved in an aqueous solution is satisfied.
Additionally, an Arrhenius chemical must donate, or produce, a particular type of ion. Therefore, a solute can only be classified as an Arrhenius acid if a proton, H+1, is written on the right, or product, side of the arrow in a solution equation. Because a hydrogen ion, H+1, is present on the right side of the solution equation that is shown above, a protonis produced, or donated, during the dissociation of HNO3.
Based on the analysis that is described in the previous paragraphs, the indicated solute, HNO3, can be definitively classified as an Arrhenius acid. This definition-driven assignment aligns with the "shortcut" conclusion that was established above.