Understanding the Reaction
When a weak acid (HA) reacts with a strong base (like NaOH), it undergoes a neutralization reaction, producing water and a salt (A-). The ionization constant (Ka) of the weak acid is given as 10^-4.
Ionization of Weak Acid
- The ionization of the weak acid can be represented as:
- HA ⇌ H+ + A-
- The equilibrium expression for this reaction is:
- Ka = [H+][A-] / [HA]
Neutralization Reaction
- When the weak acid reacts with a strong base, the reaction can be summarized as:
- HA + OH- ⇌ A- + H2O
- The equilibrium constant (K) for this reaction can be expressed as:
- K = [A-][H2O] / [HA][OH-]
Relating Ka and Kb
- For the weak acid, we can also consider the base ionization constant (Kb) of the conjugate base (A-):
- Kb = Kw / Ka
- Where Kw is the ion product of water (1 x 10^-14 at 25°C).
- Using the given Ka:
- Kb = 1 x 10^-14 / 10^-4 = 1 x 10^-10
Equilibrium Constant Calculation
- The equilibrium constant for the neutralization reaction (K) is related to Ka and Kb:
- K = Ka * Kb
- K = (10^-4) * (1 x 10^-10) = 1 x 10^-14
Conclusion
- The equilibrium constant for the reaction between the weak acid and strong base is:
- K = 1 x 10^-14.
This indicates the extent of the reaction under equilibrium conditions, showing that the neutralization of a weak acid by a strong base is highly favored.