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Acetic Acid Dissociation Constant:
Ka = dissociation constant for acetic acid at 25°C. Literature value.
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The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution. For acetic acid, it represents the equilibrium constant for the dissociation reaction: CH₃COOH ⇌ CH₃COO⁻ + H⁺. The literature value for acetic acid at 25°C is 1.8 × 10⁻⁵.
The calculator uses the weak acid dissociation formula:
Where:
Explanation: This formula applies to weak acids where the degree of dissociation is small, and we can make the approximation that [H⁺] = [A⁻] and [HA] ≈ C - [H⁺].
Details: Knowing the Ka value is crucial for understanding acid strength, predicting pH of solutions, designing buffer systems, and in various chemical and biological applications. Acetic acid's Ka indicates it's a weak acid.
Tips: Enter the initial concentration of acetic acid in molarity (M), measured pH value, and temperature in Celsius. Ensure concentration is greater than the calculated [H⁺] concentration for valid results.
Q1: Why is acetic acid's Ka 1.8 × 10⁻⁵?
A: This value indicates acetic acid is a weak acid that only partially dissociates in water, with about 0.4% dissociation at 0.1 M concentration.
Q2: How does temperature affect Ka?
A: Ka values are temperature-dependent. The provided literature value is for 25°C. Temperature changes can shift the equilibrium position.
Q3: What is pKa and how is it related to Ka?
A: pKa = -log₁₀(Ka). For acetic acid, pKa = -log(1.8 × 10⁻⁵) = 4.74. Lower pKa means stronger acid.
Q4: When is the approximation [HA] ≈ C valid?
A: This approximation works well for weak acids (Ka < 10⁻³) where dissociation is less than 5%. For stronger acids, the exact quadratic formula should be used.
Q5: What are common sources of error in Ka determination?
A: Temperature fluctuations, pH meter calibration errors, impurity in acetic acid sample, and ignoring activity coefficients can affect accuracy.