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Acid Dissociation Constant (Kₐ) Formula:
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The acid dissociation constant (Kₐ) is a quantitative measure of the strength of an acid in solution. It describes the equilibrium between the undissociated acid and its dissociation products. For acetic acid, this represents how readily it donates protons in aqueous solution.
The calculator uses the acid dissociation constant formula:
Where:
Explanation: The formula calculates the dissociation constant from initial pH measurements, assuming the acid is weak and the approximation holds true for dilute solutions.
Details: Accurate Kₐ determination is crucial for understanding acid strength, predicting buffer capacity, calculating pH of solutions, and designing chemical processes involving acid-base reactions.
Tips: Enter pH value between 0-14 and initial acid concentration in mol/L. Ensure measurements are taken at consistent temperature as Kₐ is temperature-dependent.
Q1: Why use initial pH for Kₐ calculation?
A: Initial pH provides the hydrogen ion concentration before significant dilution or reaction occurs, giving the most accurate representation of the acid's inherent dissociation tendency.
Q2: What is the typical Kₐ value for acetic acid?
A: Acetic acid has a Kₐ of approximately 1.8 × 10⁻⁵ mol/L at 25°C, classifying it as a weak acid.
Q3: When is this approximation valid?
A: This approximation works best for weak acids where [H⁺] is much smaller than C, and for concentrations where activity coefficients are close to 1.
Q4: How does temperature affect Kₐ?
A: Kₐ values are temperature-dependent. Most acids show increased dissociation with rising temperature due to endothermic nature of dissociation.
Q5: Can this method be used for strong acids?
A: No, this method is designed for weak acids. Strong acids are essentially completely dissociated, making Kₐ calculation from pH impractical.