1. Dissociation:
* Strong base: A strong base like NaOH completely dissociates in water, releasing hydroxide ions (OH-) into the solution.
* Weak acid: A weak acid like acetic acid (CH3COOH) only partially dissociates in water, releasing a small amount of hydrogen ions (H+) and its conjugate base (CH3COO-).
2. Neutralization:
* The hydroxide ions (OH-) from the strong base react with the hydrogen ions (H+) from the weak acid to form water (H2O).
* This reaction consumes the H+ ions, shifting the equilibrium of the weak acid's dissociation to the right, causing more of the weak acid to dissociate.
3. Salt Formation:
* The remaining conjugate base of the weak acid (CH3COO-) combines with the metal cation from the strong base (Na+) to form a salt (sodium acetate, CH3COONa).
4. pH Change:
* The reaction shifts the pH of the solution towards neutrality. Since the strong base is in excess, the resulting solution will be slightly basic (pH greater than 7).
Key Features:
* Buffer Formation: If the weak acid and its conjugate base are present in significant amounts, the resulting solution can act as a buffer, resisting changes in pH.
* Incomplete Neutralization: Unlike the reaction of a strong acid and strong base, the neutralization of a weak acid by a strong base is not complete. Some of the weak acid remains undissociated, leading to a slightly basic solution.
Example:
Consider the reaction of acetic acid (CH3COOH) with sodium hydroxide (NaOH):
CH3COOH(aq) + NaOH(aq) -> CH3COONa(aq) + H2O(l)
This reaction produces sodium acetate (CH3COONa), which is a salt, and water. The solution will have a pH slightly greater than 7 due to the presence of the conjugate base of the weak acid.
In summary:
The reaction of a weak acid and a strong base results in neutralization, salt formation, and a slightly basic solution. The resulting solution may also act as a buffer depending on the relative concentrations of the weak acid and its conjugate base.
