Which of the following statements is true?
A) A buffer forms when any acid or base are mixed together
B) A buffer forms when a strong acid is mixed with a weak acid.
C) A buffer forms when a conjugate weak acid/weak base pair are mixed together.
D) A buffer forms when a weak acid is mixed with a weak base.
The Correct Answer and Explanation is:
The correct answer is D) A buffer forms when a weak acid is mixed with a weak base.
Explanation:
A buffer is a solution that resists changes in pH when small amounts of acid or base are added. Buffers are typically made up of a weak acid and its conjugate base, or a weak base and its conjugate acid. These components work together to maintain the pH of a solution by neutralizing added acids or bases.
In this case:
- Weak acid: A weak acid only partially dissociates in water. This means it does not release all of its hydrogen ions (H+) into the solution.
- Weak base: Similarly, a weak base only partially accepts hydrogen ions from the solution.
When a weak acid and a weak base are mixed together, they can interact in such a way that they form a buffer system. The weak acid can donate hydrogen ions (H+) when the pH increases (in the presence of a base), while the weak base can accept hydrogen ions when the pH decreases (in the presence of an acid). This buffering action helps to maintain a relatively stable pH in the solution.
Why the other options are incorrect:
- A) A buffer forms when any acid or base are mixed together: This is incorrect because not all acids and bases form buffers. A buffer requires a specific pairing of a weak acid with its conjugate base, or a weak base with its conjugate acid. Strong acids or bases cannot form effective buffers because they dissociate completely in water.
- B) A buffer forms when a strong acid is mixed with a weak acid: This is incorrect because mixing a strong acid with a weak acid does not create a buffer. The strong acid would dominate, dissociating completely and significantly lowering the pH, not allowing the weak acid to function in a buffering capacity.
- C) A buffer forms when a conjugate weak acid/weak base pair are mixed together: This is close, but the correct terminology should involve either a weak acid and its conjugate base or a weak base and its conjugate acid. A conjugate acid/base pair from two weak components will create a buffer, but both must be weak acid/base pairs, not just weak components alone.
Therefore, the correct and complete definition of a buffer system involves mixing a weak acid with a weak base, which allows for a dynamic equilibrium that resists pH changes.