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Equilibrium Constant Equation:
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The equilibrium constant (Keq) calculated from pKa represents the acid dissociation constant for weak acids in aqueous solution. It quantifies the extent to which an acid donates protons in solution and is fundamental to understanding acid-base chemistry.
The calculator uses the equilibrium constant equation:
Where:
Explanation: The equation converts the logarithmic pKa scale to the linear equilibrium constant scale, where lower pKa values correspond to stronger acids and higher Keq values.
Details: Calculating Keq from pKa is essential for predicting acid strength, understanding buffer systems, calculating pH of solutions, and designing chemical reactions in analytical chemistry, biochemistry, and pharmaceutical sciences.
Tips: Enter the pKa value as a dimensionless number. The calculator will compute the corresponding equilibrium constant. Typical pKa values range from -10 for strong acids to 50 for very weak acids.
Q1: What is the relationship between pKa and acid strength?
A: Lower pKa values indicate stronger acids, as pKa = -log(Ka). A difference of 1 pKa unit represents a tenfold difference in acid strength.
Q2: What are typical pKa values for common acids?
A: Strong acids: pKa < 0 (HCl: -6.3, H₂SO₄: -3), weak acids: pKa > 0 (acetic acid: 4.76, carbonic acid: 6.3), very weak acids: pKa > 10.
Q3: How does temperature affect pKa values?
A: pKa values are temperature-dependent. Most change by 0.01-0.03 units per °C, so measurements should specify temperature (usually 25°C).
Q4: Can this calculator be used for bases?
A: For conjugate bases, use pKb = 14 - pKa (in water at 25°C), then apply the same formula: Kb = 10^(-pKb).
Q5: What are the limitations of this calculation?
A: This assumes ideal behavior and constant temperature. For precise work, consider ionic strength effects and temperature corrections.