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pH Formula for Salt of Weak Acid/Base:
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This calculator determines the pH of a 1.0 M solution of ammonium formate, which is a salt formed from a weak acid (formic acid) and a weak base (ammonia). The pH calculation considers the dissociation constants of both the acid and base components.
The calculator uses the formula:
Where:
Explanation: This formula applies specifically to salts of weak acids and weak bases at 1.0 M concentration, where the pH depends on the relative strengths of the conjugate acid and base.
Details: Accurate pH calculation is essential for understanding chemical behavior in solution, predicting reaction outcomes, and designing buffer systems for various applications in chemistry and biology.
Tips: Enter the acid dissociation constant (Ka) and base dissociation constant (Kb) in mol/L. Both values must be positive numbers. The concentration is fixed at 1.0 M for this specific calculation.
Q1: Why is the concentration fixed at 1.0 M?
A: This calculator is specifically designed for 1.0 M ammonium formate solutions. Different concentrations would require a modified formula.
Q2: What are typical Ka and Kb values for ammonium formate?
A: For formic acid, Ka ≈ 1.8 × 10⁻⁴; for ammonia, Kb ≈ 1.8 × 10⁻⁵. These values yield a pH of approximately 6.5 for 1.0 M ammonium formate.
Q3: Does this formula work for other salts?
A: This specific formula applies to salts of weak acids and weak bases. Different types of salts (strong acid/weak base, weak acid/strong base) require different calculation methods.
Q4: Why is the pH calculation logarithmic?
A: pH is defined as -log[H⁺], making it a logarithmic scale. The relationship between Ka, Kb, and pH is naturally logarithmic due to the nature of acid-base equilibria.
Q5: Are there limitations to this calculation?
A: This calculation assumes ideal behavior, constant temperature (25°C), and neglects activity coefficients. It may be less accurate at very high or very low concentrations.