Weak Acid + Strong Base ??? (1 Viewer)

[el_manu]

Why does a Weak Acid + Strong Base go to completion?

Give an example as well?

I thought only strong acid strong base went to completion.

 

[el_manu]

Help!!! PLease.

 

[pomsky]

It goes to completion because it's a neutralisation reaction. All neutralisation reactions (base + acid, regardless of strength) is a forward reaction that produces a salt and water.

The salt can then further dissociate / react with water to produce hydronium (making it an acidic salt) or hydroxide (basic salt). Generally speaking a weak acid + strong base will result in a basic salt, while a weak base + strong acid will result in an acidic salt. A strong base and a strong acid will produce a neutral salt. We cannot determine the general acidity of the salt a weak base + a weak acid will produce because it can be either.

The above principle is based on the fact of conjugate acid/ base strengths.

 

[Ekman]

Well to explain the process of neutralisation reactions going to completion in terms of Le Chatlier's Principle, here is the logic using examples:
Weak Acid: CH3COOH <---> CH3COO- + H+
Strong Base: NaOH ---> Na+ + OH-
So as you add more NaOH to the acetic acid solution, the H+ concentration decreases, as the OH- reacts with the H+ ions. According to Le Chatlier's principle, a chemical system at equilibrium will shift to minimise the disturbance of a change in concentration. Therefore the equilibrium for the acetic acid disassociation will shift to the RHS, in order to minimise the decrease of H+ ions. As you continue to add more and more NaOH, the equilibrium will shift to the right so much that it will become a unidirectional disassociation, hence the neutralisation reaction will go in one direction.