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Ka Calculation Formula:
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The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation reaction of an acid. From pH and concentration, we can calculate Ka using the relationship between hydrogen ion concentration and acid concentration.
The calculator uses the formula:
Where:
Explanation: This formula is derived from the equilibrium expression for weak acid dissociation and assumes that the acid is monoprotic and that the concentration of H⁺ comes primarily from the acid dissociation.
Details: Knowing the Ka value is essential for understanding acid strength, predicting pH of solutions, designing buffer systems, and studying chemical equilibria in various chemical and biological systems.
Tips: Enter the pH value (0-14) and the initial concentration of the acid in mol/L. The calculator will compute both the hydrogen ion concentration and the acid dissociation constant (Ka).
Q1: What is the relationship between pH and [H⁺]?
A: pH = -log[H⁺], so [H⁺] = 10^(-pH). This is the fundamental relationship used in the calculation.
Q2: When is this calculation valid?
A: This calculation is valid for weak acids where the approximation [H⁺] ≈ √(Ka·C) holds true and for concentrations where C > [H⁺].
Q3: What are typical Ka values for common acids?
A: Strong acids have Ka > 1, weak acids have Ka < 1. For example, acetic acid has Ka ≈ 1.8×10⁻⁵, while hydrochloric acid is considered strong with Ka >> 1.
Q4: Can this be used for polyprotic acids?
A: This specific formula is designed for monoprotic acids. Polyprotic acids require more complex calculations considering multiple dissociation steps.
Q5: What are the limitations of this calculation?
A: The calculation assumes ideal behavior, neglects activity coefficients, and may not be accurate for very dilute solutions or very strong acids where additional factors need consideration.