Posted by Alison on .
Two of the questions my teacher put on the review sheet for our Acid/Base test are
1) what is the characteristic property of a buffer solution?
and 2) what does a buffer solution contain?
i think a buffer solution contains a weak acid and its conjugate base or a weak base and its conjugate acid but what is the difference between these two questions?
are the characteristic properties of a buffer solution different from what a buffer solution contains?
Yes. You answered #2 and it's a VERY good answer. The characteristic property of a buffered (I don't like to see them called buffer solution--they are "buffered" solution)===
A buffered solution resists a change in pH. To expand, if one adds a strong acid to a non-buffered solution (such as adding HCl), the pH changes dramatically. But if the same amount of HCl is added to a buffered solution, the pH changes but nonly slightly. The same for a strong base. Add a strong base, such s NaOH, to a buffered solution and the pH changes only slightly. Do you know why they work that way? From your definition, lets say we have an acetic acid/ sodium acetate buffered solution.
Here they are.
If we add NaOH, it is neutralized by the CH3COOH, forming more CH3COONa. The end result is that we have transformed a strong base into a the salt. So we have a little more salt (the base) and a little less acid and the pH changes slightly.
If we add a strong acid, such as HCl, the H^+ immediately gets tied up with the acetate, like this,
CH3COO^- + H^+ ==> CH3COOH.
The net result is that we have transformed a strong acid into a weak one. The acid concn increases a little, the base concn(acetate) decreases slightly, and the pH changes only slightly.