Here's why:
* Buffers resist changes in pH. They are solutions that can neutralize small amounts of added acid or base without significant changes in pH.
* Hydroxide ions are basic. Adding a large number of hydroxide ions to a solution will make it more basic (increase the pH).
* To form a buffer, you need a weak acid and its conjugate base (or a weak base and its conjugate acid). These pairs can neutralize both added acid and base.
Think of it like this:
* Adding hydroxide ions is like adding base to a solution. It will increase the pH.
* A buffer needs both acidic and basic components to be effective. Adding only hydroxide ions will make the solution more basic, not create a buffer.
Example:
You wouldn't create a buffer by simply adding a large amount of NaOH (which releases hydroxide ions) to water. This would just make a strong basic solution.
To create a buffer, you would need to add a weak acid (like acetic acid) and its conjugate base (acetate ions).
