Calculating Percent Dissociation Of A Weak Acid A Student Prepares A 0.49 M Aqueous Solution Of 4-Chlorobutanoic Acid (C,H,CICO,H). Calculate The Fraction Of 4-Chlorobutanoic Acid That Is In The Dissociated Form In His Solution. Express Your Answer As A Percentage. You Will Probably Find Some Useful Data In The ALEKS Data Resource. Round Your Answer To 2 digits
The Correct Answer and Explanation is :
To determine the fraction of 4-chlorobutanoic acid dissociated in a 0.49 M aqueous solution, we need to calculate its percent dissociation. This involves understanding the acid dissociation constant (Ka) and applying it to the dissociation equilibrium.
Step 1: Understanding the Acid Dissociation Constant (Ka)
The dissociation of 4-chlorobutanoic acid (C₄H₇ClO₂) in water can be represented as:
[ \text{C₄H₇ClO₂} \rightleftharpoons \text{C₄H₆ClO₂}⁻ + \text{H}⁺ ]
The strength of this acid is quantified by its acid dissociation constant (Ka). A lower pKa value indicates a stronger acid, as it dissociates more readily. For 4-chlorobutanoic acid, the pKa is approximately 4.52. citeturn0search7
Step 2: Calculating the Percent Dissociation
The percent dissociation is calculated using the formula:
[ \text{Percent Dissociation} = \left( \frac{[\text{H}⁺]}{[\text{HA}]} \right) \times 100 ]
Where:
- [H⁺] is the concentration of hydrogen ions (H⁺) in the solution.
- [HA] is the initial concentration of the acid.
Given that the pKa is 4.52, we can calculate the Ka:
[ \text{Ka} = 10^{-\text{pKa}} = 10^{-4.52} \approx 3.02 \times 10^{-5} ]
For a weak acid, the dissociation is minimal, so we can assume that the concentration of dissociated acid ([H⁺]) is much smaller than the initial concentration of the acid. Therefore, we can approximate the percent dissociation as:
[ \text{Percent Dissociation} \approx \left( \frac{[\text{H}⁺]}{[\text{HA}]} \right) \times 100 ]
Substituting the given concentration:
[ \text{Percent Dissociation} \approx \left( \frac{0.49}{0.49} \right) \times 100 = 100\% ]
Therefore, the fraction of 4-chlorobutanoic acid that is dissociated in the solution is approximately 100%.
Step 3: Conclusion
In a 0.49 M aqueous solution of 4-chlorobutanoic acid, the acid dissociates to a significant extent, resulting in a high concentration of hydrogen ions and a low pH. This indicates that the acid is relatively strong in this concentration.
Note: The calculation assumes ideal behavior and does not account for activity coefficients or other real-world factors that might slightly alter the dissociation in a concentrated solution.