Calculate Ph of 0.137 M Sodium Hexanoate Nac6h11o2
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Reviewed by Calculator Editorial Team
This calculator determines the pH of a 0.137 M solution of sodium hexanoate (NaC6H11O2) using the Henderson-Hasselbalch equation. Sodium hexanoate is a weak organic acid that dissociates in water, forming hexanoate anions and hydrogen ions.
Introduction
The pH of a solution is a measure of its acidity or alkalinity. For weak acids like sodium hexanoate, the pH can be calculated using the Henderson-Hasselbalch equation when the concentration of the acid and its conjugate base are known.
Sodium hexanoate (NaC6H11O2) is a weak acid with a pKa value of approximately 4.87. When dissolved in water, it dissociates into hexanoate anions (C6H11O2⁻) and hydrogen ions (H⁺).
Formula
The Henderson-Hasselbalch equation is used to calculate the pH of a buffer solution:
Where:
- pH - The pH of the solution
- pKa - The acid dissociation constant of the weak acid (4.87 for sodium hexanoate)
- [A⁻] - The concentration of the conjugate base (hexanoate anions)
- [HA] - The concentration of the weak acid (sodium hexanoate)
For a solution of sodium hexanoate, the concentration of the conjugate base [A⁻] is equal to the concentration of the weak acid [HA] because they are in equilibrium.
Calculation
To calculate the pH of a 0.137 M solution of sodium hexanoate:
- Identify the pKa value of sodium hexanoate (4.87)
- Determine the concentration of the weak acid [HA] (0.137 M)
- Since [A⁻] = [HA], the ratio [A⁻]/[HA] = 1
- Apply the Henderson-Hasselbalch equation: pH = pKa + log10(1) = pKa + 0 = 4.87
The pH of a 0.137 M solution of sodium hexanoate is 4.87.
Note: The pH calculation assumes the solution is at equilibrium and that the activity coefficients are equal to 1. For more accurate results, activity coefficients should be considered.
Interpretation
A pH of 4.87 indicates that the solution is acidic. This is expected for a weak acid like sodium hexanoate, which only partially dissociates in water.
The pH value provides information about the concentration of hydrogen ions in the solution. A pH of 4.87 means there are 10^-4.87 moles of hydrogen ions per liter of solution.
This pH value is typical for weak organic acids and is useful in various applications, including buffer solutions and chemical reactions.
FAQ
What is the pKa of sodium hexanoate?
The pKa of sodium hexanoate is approximately 4.87. This value represents the acid dissociation constant and indicates how strongly the acid dissociates in water.
How does the concentration of sodium hexanoate affect the pH?
The pH of a sodium hexanoate solution is primarily determined by its pKa value. The concentration of the acid affects the equilibrium between the acid and its conjugate base but does not change the pH significantly for a given pKa.
Can the pH of a sodium hexanoate solution be adjusted?
Yes, the pH of a sodium hexanoate solution can be adjusted by adding a strong acid or base. Adding a strong acid will lower the pH, while adding a strong base will raise the pH.