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Ch.16 - Aqueous Equilibria: Acids & Bases
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.16 - Aqueous Equilibria: Acids & BasesProblema 154
Capitolo 16, Problema 154

In aqueous solution, sodium acetate behaves as a strong electrolyte, yielding Na+ cations and CH3CO2 - anions. A particular solution of sodium acetate has a pH of 9.07 and a density of 1.0085 g/mL. What is the molality of this solution, and what is its freezing point?

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1
Identify the dissociation of sodium acetate in water: \( \text{CH}_3\text{COONa} \rightarrow \text{Na}^+ + \text{CH}_3\text{COO}^- \).
Use the given pH to find the concentration of \( \text{OH}^- \) ions, since the solution is basic: \( \text{pH} + \text{pOH} = 14 \).
Calculate the concentration of \( \text{CH}_3\text{COO}^- \) using the equilibrium expression for the hydrolysis of acetate ions: \( \text{CH}_3\text{COO}^- + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{COOH} + \text{OH}^- \).
Determine the molality of the solution using the concentration of \( \text{CH}_3\text{COO}^- \) and the density of the solution to find the mass of the solvent.
Calculate the freezing point depression using the formula \( \Delta T_f = i \cdot K_f \cdot m \), where \( i \) is the van't Hoff factor, \( K_f \) is the cryoscopic constant, and \( m \) is the molality.

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Electrolytes

Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. Sodium acetate, a strong electrolyte, completely dissociates into sodium (Na+) and acetate (CH3CO2-) ions in solution. Understanding the behavior of electrolytes is crucial for calculating properties like pH and colligative effects, which are relevant to the freezing point of the solution.
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Electrolytes and Strong Acids

pH and Acid-Base Chemistry

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. A pH of 9.07 indicates a basic solution, which can affect the dissociation of weak acids and bases. In the case of sodium acetate, the acetate ion can act as a weak base, influencing the overall pH and the calculations related to the solution's properties.
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pH of Strong Acids and Bases

Colligative Properties

Colligative properties are physical properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute. These properties include boiling point elevation and freezing point depression. To determine the freezing point of the sodium acetate solution, one must calculate its molality, which is essential for applying the freezing point depression formula.
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Colligative Properties
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