8.6 How Salts Can Change the pH of a Solution of Water

Salts can affect the pH of a solution when dissolved in water due to the dissociation of their ions. When certain salts dissolve in water, they can produce either acidic, basic, or neutral solutions depending on the nature of the ions they contain.
Salts derived from strong acids and strong bases: Salts like sodium chloride (NaCl), potassium bromide (KBr), and potassium nitrate (KNO3) are formed from the combination of strong acids and strong bases. These salts generally do not affect the pH of the solution significantly. They dissociate completely into their respective ions (Na+, Cl-, K+, Br-, NO3-) and do not contribute to the concentration of hydrogen ions (H+) or hydroxide ions (OH-) in the solution. Therefore, they create a neutral solution (pH 7).
Salts derived from strong acids and weak bases or weak acids and strong bases: These salts can affect the pH of a solution. For example:
a. Salts from strong acids and weak bases (e.g., ammonium chloride NH4Cl): The ammonium ion (NH4+) is acidic because it can react with water to produce hydronium ions (H3O+), thereby lowering the pH of the solution slightly.
b. Salts from weak acids and strong bases (e.g., sodium acetate CH3COONa): The acetate ion (CH3COO-) is basic because it can react with water to produce hydroxide ions (OH-), leading to a slight increase in pH.
Salts derived from weak acids and weak bases: The pH effect of these salts depends on the relative strengths of the acid and base they are derived from. They can produce acidic, basic, or neutral solutions based on which component is stronger.
In summary, the influence of a salt on the pH of a solution depends on the ions it releases upon dissolving and whether those ions have acidic, basic, or neutral properties. This interaction with water and subsequent ionization determines whether the solution becomes more acidic, more basic, or remains neutral.