ph of aqueous solution of one of the following salts is independent of its concentration. the salt
Which salt has a pH of its aqueous solution independent of its concentration?
The pH of an aqueous solution of a salt can be influenced by several factors, including the nature of the cation and anion that make up the salt. However, there are specific scenarios where the pH is independent of the concentration of the solution. Let’s explore these scenarios:
Strong Acids and Bases: Neutral Salts
- Salts Formed from Strong Acids and Strong Bases: These salts are neutral salts, such as sodium chloride (NaCl), potassium nitrate (KNO₃), or barium sulfate (BaSO₄), and dissociate completely in water without affecting the pH. These salts do not hydrolyze in water and do not alter the concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻) in the solution. As a result, the pH of solutions of these salts is typically neutral (around 7) and independent of concentration, provided the solution is dilute enough to prevent significant ionic strength effects.
Special Case: Salts from Amphiprotic Ions
One of the most interesting cases is salts formed from amphiprotic ions, such as sodium hydrogen carbonate (NaHCO₃) or sodium hydrogen phosphate (Na₂HPO₄). These salts contain ions capable of both accepting and donating protons, thus exhibiting a buffer-like behavior under certain conditions.
An Example: Sodium Salts of Weak Acids
To further elaborate, consider sodium acetate (CH₃COONa), a salt derived from acetic acid (CH₃COOH) and sodium hydroxide (NaOH). When dissolved in water, sodium acetate dissociates to give acetate ions (CH₃COO⁻) and sodium ions (Na⁺). The acetate ion, being the conjugate base of a weak acid, tends to slightly shift the solution’s pH to the basic side. However, the pH isn’t strictly independent of concentration in this case, as dilution will reduce the buffering capacity.
Salts of Amphiprotic Ions That Truly Meet the Condition
A notable exception where the pH remains fixed, even at varying concentrations, involves salts formed entirely from amphiprotic ions in such a manner that the solution behaves as a buffer. This occurs often in compounds like sodium bicarbonate (NaHCO₃), where the concentrations of the bicarbonate ion and its conjugate acidity/base form balances at a pH that depends significantly on equilibrium considerations rather than concentration changes.
Visualization:
| Salt Type | pH Dependence on Concentration |
|---|---|
| Strong Acid + Strong Base Salts | Independent (Neutral, pH ~7) |
| Amphiprotic Salts | Often Independent due to buffer effects when low |
Conclusion
The salts whose aqueous solutions have a pH largely independent of their concentration are those formed between the ions of strong acids and bases or those involving amphiprotic ions with exclusive intrinsic buffering systems. Understanding these concepts is crucial when considering the chemistry involved in developing buffer solutions and other industrial applications where pH stability is essential.
If you have any more questions or need further clarification, feel free to ask!