To understand why this is, we'll need to take a look at how a buffer works.
A buffer, by definition, is a solution containing a weak acid, and it's conjugate base (usually added through the form of a salt). This can also be made by a weak base and it's conjugate acid.
The main selling point of a buffer is that it minimizes pH changes within a certain range. How? Consider the balanced chemical equation for the acid-dissociation reaction for HCN:
The idea is that you have significant concentrations of both your weak acid (
Now, if you add some strong acid (ex.
That, on an intuitive level, is how a buffer works. Your buffer satisfies those conditions, as you have concentrations of both a weak acid and conjugate base.
If you'd like some additional information on buffers, check out this video .
How do you determine in what pH range a buffer works? Learn about that here .
Hope that helps :)