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Weak Acid Dissociation Formula:
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Aqueous dissociation refers to the process where weak acids partially ionize in water, establishing an equilibrium between the undissociated acid and its ions. The extent of dissociation is quantified by the acid dissociation constant (Ka) and the initial concentration of the acid.
The calculator uses the weak acid approximation formula:
Where:
Explanation: This approximation is valid when the dissociation is small (typically less than 5%) and assumes that the concentration of H⁺ ions from water is negligible compared to that from the acid.
Details: Calculating the percentage dissociation helps in understanding the strength of weak acids, predicting pH of solutions, and designing buffer systems in various chemical and biological applications.
Tips: Enter the acid dissociation constant (Ka) as a unitless value and the concentration in molarity (M). Both values must be positive numbers. The approximation is most accurate when the calculated dissociation is less than 5%.
Q1: When is the weak acid approximation valid?
A: The approximation is valid when the percentage dissociation is less than about 5% and Ka << c.
Q2: What if the dissociation is greater than 5%?
A: For higher dissociation percentages, the quadratic formula or iterative methods should be used for more accurate results.
Q3: Does this work for weak bases?
A: A similar approximation exists for weak bases using Kb instead of Ka, but this calculator is specifically designed for weak acids.
Q4: What are typical Ka values for weak acids?
A: Weak acids typically have Ka values between 10⁻² and 10⁻¹⁰. Strong acids have Ka values much greater than 1.
Q5: Why is the percentage dissociation important?
A: It helps determine the extent of ionization, which affects the acid's conductivity, reactivity, and ability to act as a buffer.