Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (b) Using Appendix D, calculate the Ka for pyridinium bromide.

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Identify the species in solution: Pyridinium bromide dissociates into \( \text{C}_5\text{H}_5\text{NH}^+ \) and \( \text{Br}^- \). The \( \text{C}_5\text{H}_5\text{NH}^+ \) acts as a weak acid in water.

Write the equilibrium expression for the dissociation of \( \text{C}_5\text{H}_5\text{NH}^+ \): \( \text{C}_5\text{H}_5\text{NH}^+ + \text{H}_2\text{O} \rightleftharpoons \text{C}_5\text{H}_5\text{N} + \text{H}_3\text{O}^+ \).

Use the pH to find the concentration of \( \text{H}_3\text{O}^+ \): \( \text{[H}_3\text{O}^+] = 10^{-\text{pH}} \).

Assume that the initial concentration of \( \text{C}_5\text{H}_5\text{NH}^+ \) is equal to the concentration of \( \text{H}_3\text{O}^+ \) at equilibrium, since the solution is dilute.

Calculate \( K_a \) using the expression \( K_a = \frac{[\text{C}_5\text{H}_5\text{N}][\text{H}_3\text{O}^+]}{[\text{C}_5\text{H}_5\text{NH}^+]} \), where the concentrations of \( \text{C}_5\text{H}_5\text{N} \) and \( \text{H}_3\text{O}^+ \) are equal to the \( \text{H}_3\text{O}^+ \) concentration found from the pH.

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Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This means that they produce a high concentration of ions in solution, which is crucial for understanding their behavior in chemical reactions and their effect on properties like conductivity and pH.

pH and Acidity

pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or basicity. A lower pH value, such as 2.95, signifies a more acidic solution, which is relevant for calculating the dissociation of weak acids and their equilibrium constants, such as Ka.

Acid Dissociation Constant (Ka)

The acid dissociation constant (Ka) quantifies the strength of an acid in solution, representing the equilibrium between the undissociated acid and its ions. It is calculated using the concentrations of the products and reactants at equilibrium, and is essential for understanding the behavior of weak acids in solution.