posted by Anonymous .
Explain why a buffer made of equal concentrations of HF and F- does not change in pH when a small amount of HCl (a strong acid) is added to the solution. Does the HCl dissociate into ions when it is added to the solution? What do the hydrogen ions react with? Why don’t these hydrogen ions change the pH?
Buffers work because of the way they are constructed. Buffers consist of a weak acid and a salt of the weak acid. For example, HF for the weak acid and NaF as the salt.
When a strong acid, such as HCl, is added, the multiple H^+ are used up by the salt to form more of the weak acid HF.
F^- + H^+ ==> HF. Effectively you are taking a strong acid and making it into a weak acid which ionizes only partially. When we add a base, such as NaOH, to the solution, it is used up by the acid. HF + NaOH ==> NaF + H2O. So the base is neutralized by the weak acid to form the salt + water.