Explain why a mixture formed by mixing 100 mL of 0.1 M acetic acid and 50 mL of 0.1 M sodium hydroxide will act as buffer
HAc + NaOH ==> NaAc + H2O
The base neutralizes a part of the acid to make acetic acid and its salt which is the very definition of a buffer.
To understand why this mixture will act as a buffer, we need to first define what a buffer is. A buffer is a solution that can resist changes in pH when either an acid or a base is added to it. Buffers are important in various biological and chemical processes because they help maintain a stable pH.
Now let's break down why the given mixture will act as a buffer:
1. Acetic acid (CH3COOH): This is a weak acid that can partially dissociate in water. In water, acetic acid donates a proton (H+) to form the acetate ion (CH3COO-) and a hydronium ion (H3O+).
2. Sodium hydroxide (NaOH): This is a strong base that completely dissociates in water to produce sodium ions (Na+) and hydroxide ions (OH-).
When you mix these two solutions together, a neutralization reaction occurs between the acid (acetic acid) and the base (sodium hydroxide). The hydronium ion (H3O+) from the acid combines with the hydroxide ion (OH-) from the base to form water (H2O):
CH3COOH + NaOH → CH3COONa + H2O
After the neutralization reaction, the resulting solution contains a mixture of sodium acetate (CH3COONa) and water.
Here's why this mixture acts as a buffer:
1. Presence of a weak acid and its conjugate base: The acetic acid in the mixture (from the acetic acid solution) acts as the weak acid component of the buffer system, while the acetate ion (CH3COO-) from the sodium acetate acts as its conjugate base. The weak acid can donate protons, while the conjugate base can accept protons.
2. Equilibrium between the weak acid and its conjugate base: In the mixture, acetic acid and acetate ions are present. They can exist in equilibrium, meaning that acetic acid can lose protons to form acetate ions, and acetate ions can accept protons to form acetic acid. This equilibrium helps maintain a relatively stable pH in the solution.
If an acid or a base is added to the buffer solution, the equilibrium between the weak acid and its conjugate base will help minimize changes in pH. If you add more acid to the buffer solution, some of the acid will react with the acetate ions to form acetic acid, thus preventing a significant decrease in pH. Similarly, if you add more base (OH-) to the buffer solution, some of the OH- ions will react with the acetic acid to form water and acetate ions, helping to minimize the increase in pH.
In summary, the mixture formed by mixing 100 mL of 0.1 M acetic acid and 50 mL of 0.1 M sodium hydroxide acts as a buffer because it contains a weak acid (acetic acid) and its conjugate base (acetate ion), which can undergo an equilibrium reaction. This equilibrium allows the buffer solution to resist changes in pH when small amounts of acid or base are added.