The graph in Figure P15.2 shows the percent ionization of...

The graph in Figure P15.2 shows the percent ionization of two acids as a function of concentration in water. Which line describes the behavior of $\mathrm{HNO}_{3},$ and which line describes the behavior of acetic acid $\left(\mathrm{CH}_{3} \mathrm{COOH}\right) ?$ (Check your book to see figure)

Key Concepts

Percent Ionization

Percent ionization refers to the fraction of acid molecules that dissociate into ions in an aqueous solution. It is a key concept when analyzing how much an acid contributes to the concentration of hydrogen ions (H?) in the solution, and it varies with both the strength of the acid and its concentration.

Strong vs Weak Acids

This concept differentiates acids based on their ability to ionize in water. Strong acids ionize nearly completely, meaning that almost every molecule donates a proton, while weak acids only partly ionize. This distinction is crucial for understanding why strong acids maintain a high percent ionization regardless of concentration changes and why weak acids show a significant change in ionization in response to dilution.

Acid Dissociation Constant (Ka)

The acid dissociation constant (Ka) quantifies the extent of ionization of an acid in water. A larger Ka value indicates a stronger acid that ionizes more completely, whereas a smaller Ka value corresponds to a weaker acid with a lower degree of ionization. This constant is fundamental for predicting the percent ionization and the behavior of an acid under various conditions.

Effect of Concentration on Equilibrium

This concept involves understanding how changes in the concentration of reactants or products in an acid-base equilibrium can shift the balance of ionization. In weak acids, decreasing the concentration of the acid can lead to an increase in percent ionization as the system adjusts to maintain equilibrium, a phenomenon explained by Le Chatelier's principle. For strong acids, the effect of concentration changes is minimal since they are nearly completely ionized.

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