The equilibrium concentration of acetic acid (CH₃COOH) in the solution is 1.000 M.
Equilibrium Concentration of Acetic Acid
When acetic acid, a weak acid, dissolves in water, it reaches an equilibrium where it partially dissociates into acetate ions (CH₃COO⁻) and hydrogen ions (H⁺). The concentration of each species at equilibrium is crucial for understanding the solution's properties.
For a specific solution of acetic acid, the measured equilibrium concentration of undissociated acetic acid is found to be 1.000 M. This value represents the amount of acetic acid that remains in its molecular form, not having ionized into its constituent ions.
The equilibrium state of this particular acetic acid solution can be summarized as follows:
| Species | Equilibrium Concentration (M) |
|---|---|
| Acetic Acid (CH₃COOH) | 1.000 |
| Acetate Ion (CH₃COO⁻) | 0.0042 |
| Hydrogen Ion (H⁺) | 0.0042 (inferred from CH₃COO⁻) |
Understanding Acetic Acid Equilibrium
Acetic acid (CH₃COOH) is a weak acid, meaning it does not fully dissociate in water. Instead, it establishes an equilibrium described by the following equation:
CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)
At equilibrium, the rates of the forward (dissociation) and reverse (recombination) reactions are equal, resulting in constant concentrations of reactants and products.
- Undissociated Acetic Acid: A significant portion, 1.000 M in this case, remains as intact CH₃COOH molecules.
- Acetate Ions: Only a small fraction dissociates, forming 0.0042 M of acetate ions.
- Hydrogen Ions: The concentration of hydrogen ions (H⁺) is equal to the concentration of acetate ions produced, which is 0.0042 M. The pH of a solution is directly related to the hydrogen ion concentration (pH = -log[H⁺]). For this solution, the pH would be calculated as -log(0.0042), which is approximately 2.38. This acidic pH confirms the presence of hydrogen ions produced by the acetic acid's partial dissociation.
Key Takeaways from Acetic Acid Solutions
- Partial Dissociation: The high concentration of undissociated acetic acid (1.000 M) compared to its ions (0.0042 M) highlights its nature as a weak acid.
- pH Indication: The resulting pH of 2.38 is characteristic of a moderately acidic solution, driven by the relatively low concentration of H⁺ ions compared to strong acids.
- Equilibrium Constant: The equilibrium constant (Ka) for acetic acid, also known as the acid dissociation constant, can be calculated using these equilibrium concentrations, providing insight into the acid's strength.
