Acid-Base Reactions and Buffers
Introduced| English |
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| buffer/ˈbʌfə/ |
A solution that resists change
- Add a drop of strong acid to water and the pH plunges.
- But add it to blood, and the pH barely budges.
- Something in there soaks up the shock.
- That protective mixture is the star of this lesson.
The buffer recipe
- A buffer 缓冲溶液 resists changes in pH.
- It contains a weak acid and its conjugate base together.
- Both partners are present in significant amounts.
A buffer is made from...
A buffer pairs a weak acid with its conjugate base.
A working buffer must contain both a weak acid and its conjugate ____.
Both partners are needed to absorb acid and base.
Soaking up acid or base
- Add acid, and the conjugate base neutralizes it.
- Add base, and the weak acid neutralizes it.
- Either way, the pH changes only a little.
When strong acid is added to a buffer, it is neutralized by the...
The conjugate base reacts with the added $\text{H}^+$.
When strong base is added to a buffer, it is neutralized by the...
The weak acid reacts with the added $\text{OH}^-$.
Keeping systems stable
- Blood is buffered to stay near pH 7.4.
- Many reactions need a steady pH to work.
- A buffer holds that pH against small disturbances.
Is it a buffer?
Sort each mixture by whether it forms a buffer.
A buffer resists large changes in pH when small amounts of acid or base are added.
That resistance is exactly what a buffer does.
A buffer holds both acetic acid and acetate. You add a little strong acid. What happens?
- The acetate (the conjugate base) reacts with the added acid.
- So the pH drops only slightly.
A buffer can be overwhelmed if enough acid or base is added.
Buffers only handle small additions before failing.
A buffer needs both a weak acid and its conjugate base present -- a strong acid alone cannot buffer. It only resists small additions; enough acid or base will overwhelm it. And it minimizes the pH change, it does not prevent it entirely.
A buffer is a weak acid together with its conjugate base, and it resists pH change: the conjugate base neutralizes added acid while the weak acid neutralizes added base. It only softens small disturbances (like keeping blood near pH 7.4), and can be overwhelmed.