Lactic acid (CH3 CH(OH) COOH) has one acidic hydrogen. A 0.10 M solution of lactic acid has a pH

step 1 Lactic acid has one acetic hydrogen. The given solution has a pH of 2 .44. We calculate the valu

Lactic acid (CH3 CH(OH) COOH) has one acidic hydrogen. A...

Key Concepts

Acid Dissociation Constant (Ka)

Ka is a measure of the extent to which an acid dissociates in solution. It is defined by the equilibrium expression Ka = [H+][A–]/[HA] for the reaction in which the acid (HA) donates a proton to form its conjugate base (A–) and a hydrogen ion (H+). A larger Ka value signifies a stronger acid that ionizes more completely in solution.

Acid-Base Equilibrium

Acid-base equilibrium refers to the state where the rate of dissociation of the acid matches the rate of the reverse reaction, establishing constant concentrations of reactants and products. Understanding this equilibrium and its associated expression is crucial for linking the observed pH of a solution to the concentration of ions present, thus allowing for the calculation of Ka.

pH is a logarithmic scale that quantifies the concentration of hydrogen ions in a solution. It is defined as pH = -log[H+]. This concept is essential because it provides a direct connection between the measurable acidity of a solution and the concentration of hydrogen ions produced by the dissociation of an acid.

Weak Acid Approximation

For weak acids, the degree of dissociation is small relative to their initial concentration. This approximation simplifies equilibrium calculations by assuming that the change in concentration due to dissociation is negligible compared to the initial concentration. This simplification is particularly useful when calculating Ka, though it must be confirmed that the approximation does not significantly affect the accuracy of the result.

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