When #HCl# and #NH_3# are mixed why is the buffer #NH_3-NH_4Cl#?
Because a buffer solution is composed of a solution of a weak base, and its conjugate base (or vice versa) in appreciable quantities.
So how does this help us? You have an solution that is stoichiometric in ammonia; immediately you add hydrochloric acid, this protonates the ammonia, and now you both
Given ammonia and ammonium chloride, you have a buffer system. On the other hand, I could form a buffer from ammonium chloride, if I added potassium hydroxide:
In the second example, the strong base potassium hydroxide immediately deprotonates ammonium chloride, but it delivers ammonia in solution to act as a buffer with the unreacted ammonium chloride.
When you perform these weak base/strong acid or strong acid/weak base titrations, and plot a curve, the first region of the titration is often known as the buffer region because, from the above, that is precisely what it is, and the