Chapter 9: Problem 129
The conductivity of \(0.01 \mathrm{~mol} / \mathrm{dm}^{3}\) aqueous acetic acid at \(300 \mathrm{~K}\) is \(19.5 \times 10^{-5} \mathrm{ohm}^{-1} \mathrm{~cm}^{-1}\) and limiting molar conductivity of acetic acid at the same temperature is \(390 \mathrm{ohm}^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} .\) The degree of dissociation of acetic acid is (a) \(0.05\) (b) \(0.5 \times 10^{-2}\) (c) \(5 \times 10^{-7}\) (d) \(5 \times 10^{-3}\)
Short Answer
Step by step solution
Identify Given Values
Compute Molar Conductivity
Determine Degree of Dissociation
Choose the Correct Answer
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Degree of Dissociation
- The degree of dissociation, denoted as \( \alpha \), tells us the fraction of the original substance that has dissociated into ions.
- Calculated by taking the molar conductivity of a solution and dividing it by its limiting molar conductivity (\( \alpha = \frac{\Lambda}{\Lambda^0} \)).
- A larger value of \( \alpha \) indicates more dissociation, while a smaller value suggests less dissociation.
Molar Conductivity
- Calculated using the formula \( \Lambda = \frac{\kappa \times 1000}{C} \), where \( \kappa \) is the conductivity and \( C \) is the concentration.
- It provides insight into how conductive a solution will be as the concentration changes.
- Molar conductivity typically increases as the concentration of ions decreases, because ions move more freely in less concentrated solutions.
Limiting Molar Conductivity
- Symbolized as \( \Lambda^0 \), it represents the upper limit of conductivity for a solution.
- This measure is determined under the assumption that there's no interaction between ions, which only occurs in very dilute solutions.
- It allows comparison between different electrolytes, as it reflects the inherent ability of ions to conduct electricity.
Solution Conductivity
- Measured in ohm\(^{-1}\) cm\(^{-1}\), it reflects the ease with which electric current can pass through a solution.
- Higher conductivity indicates more available charge carriers in the solution, such as ions from dissociated molecules.
- The conductivity of a solution can change with temperature and concentration, affecting the overall behavior and efficiency of the solution in conducting electricity.
Ionic Dissociation
- Only a fraction of the acid's molecules will dissociate to form hydronium ions \( H_3O^+ \) and acetate ions \( CH_3COO^- \).
- Partial dissociation is characterized by a specific equilibrium condition where the forward and reverse reactions occur at equal rates.
- The extent of dissociation is influenced by factors such as temperature and concentration.
Chemical Equilibrium
- At equilibrium, the concentration of reactants and products remains constant over time, though the reaction continues to occur both forward and backward.
- For acetic acid, equilibrium involves its dissociation into ions and the recombination of those ions back into acetic acid molecules.
- Le Chatelier's principle explains how changes in concentration, temperature, or pressure affect chemical equilibrium, allowing predictions of the system's response to different conditions.