Equilibrium constant of a weak acid. In discussing the equilibrium involved when a weak acid is added to water, a heterogeneous equilibrium forms in which aqueous acid molecules, HB aq , react with liquid water to form aqueous hydronium ions and aqueous anions, B- aq. When the equilibrium in question occurs in solution, the chemical formulas enclosed in brackets in the equilibrium constant expression represent the molarities of the substances. It is convenient to represent the proton transfer as a simple ionisation.
The Ka value of some weak acid in the order of decreasing strength are listed in tabular form. The weaker the acid,the smaller the value of Ka. There are several ways to determine Ka of a weak acid. Aspirin is a weak organic acid whose molecular formula may be written as HC9H7O4.
The derivation is involved, but the Henderson-Hasselbach equation relates these quantities in the following manner:. Example: The K a of acetic acid, the main component of vinegar, is 1. This means that at pH lower than acetic acid's pKa, less than half will be dissociated, or ionized; at higher pH values, more than half will be ionized.
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont.
Formerly with ScienceBlogs. More about Kevin and links to his professional work can be found at www. Example: What is the pH of a solution of 0. How to Calculate the Percentage of Ionization Given How to Calculate Percent Dissociation. How to Calculate the pH of a Strong Acid. How to Calculate Hydrogen Ion Concentration. What Is the Meaning of a Ph Scale?
How to Calculate Titratable Acidity. How to Calculate Alkalinity After Titration. How to Calculate Kb From Ka. How to Determine Conjugate Bases of Acids. How to Calculate ph And pOH. How to Calculate Ka From Ph. How Is pH Calculated?
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