Lithium nitrate (\(\text{LiNO}_3\)) is an inorganic salt formed when the lithium cation (\(\text{Li}^+\)) bonds ionically with the nitrate anion (\(\text{NO}_3^-\)). When this solid is dissolved in water, the resulting solution is classified using the pH scale. The pH scale ranges from 0 to 14, where values below 7 indicate acidity, values above 7 indicate basicity, and a value of 7 indicates neutrality.
The pH Classification of Lithium Nitrate
When lithium nitrate is dissolved in water, it forms a neutral solution. This means the concentration of hydrogen ions and hydroxide ions remains balanced. The solution’s pH value is therefore approximately 7, which is the midpoint of the pH scale.
How Salts Derive Their Acidity or Basicity
Salts are ionic compounds formed through the neutralization reaction between an acid and a base. The resulting pH of a salt solution depends entirely on the relative strengths of these original parent compounds. Chemists classify parent acids and bases as either “strong,” meaning they ionize completely in water, or “weak,” meaning they ionize only partially.
The key to determining a salt solution’s pH lies in hydrolysis, the reaction of a salt’s constituent ions with water. Ions derived from strong parent compounds generally do not react significantly with water. These spectator ions will not alter the natural balance of \(\text{H}^+\) and \(\text{OH}^-\) ions already present.
Conversely, ions derived from a weak parent compound will undergo hydrolysis. For example, the conjugate base of a weak acid reacts with water to produce hydroxide ions (\(\text{OH}^-\)), making the solution basic. The conjugate acid of a weak base reacts to produce hydrogen ions (\(\text{H}^+\)), resulting in an acidic solution. Neutrality is maintained only when neither ion participates significantly in this reaction.
Why Lithium Nitrate is Chemically Neutral
The neutrality of lithium nitrate is explained by the strength of its parent acid and parent base. Lithium nitrate is composed of the lithium cation (\(\text{Li}^+\)) and the nitrate anion (\(\text{NO}_3^-\)). The lithium cation is the remnant of the strong base Lithium Hydroxide (\(\text{LiOH}\)).
The nitrate anion (\(\text{NO}_3^-\)) is the remnant of the strong acid Nitric Acid (\(\text{HNO}_3\)). Because both parent compounds are classified as strong, neither the \(\text{Li}^+\) nor the \(\text{NO}_3^-\) ions tend to react with water molecules. The ions simply dissociate and remain surrounded by water, a process called hydration, without engaging in hydrolysis.
Since neither the lithium ion nor the nitrate ion removes or contributes excess \(\text{H}^+\) or \(\text{OH}^-\) ions, the neutral equilibrium of the water is not disturbed. The concentration of \(\text{H}^+\) remains equal to the concentration of \(\text{OH}^-\) in the solution. This indifference to the water’s natural ionization is why a lithium nitrate solution maintains a neutral pH of 7.