If you mixed equal volume of .1 M HCl and .20 M Tris (pka=8.3), IS THE RESULTING SOLUTION A BUFFER SOLUTION? Why? or Why not?
TRIS is (HOCH2)3CNH2. The reaction with HCl forms a salt.
(HOCH2)3CNH2 + HCl ==> (HOCH2)3NH3Cl
If we start with some volume (the problem states equal volumes but it's easier to assume some volume, for example, 100 mL), then
mmoles TRIS = 100 x 0.2 = 20 to start.
mmoles HCl = 100 x 0.1 = 10 to start.
After the reaction, all of the HCl will be consumed, 10 mmoles of the salt will form, and 10 mmoles TRIS will be left unreacted. Thus, we have the salt + TRIS (a base) which makes a buffered solution. You can calculate the pH.
pH = pKa + log (base/acid)
pH = 8.3 + log (10/10)
pH = 8.3
To determine whether the resulting solution is a buffer solution, we need to compare the concentrations of the acidic and basic components of the potential buffer system. A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in approximately equal concentrations.
In this case, you have mixed HCl, which is a strong acid, and Tris, which acts as a base. Tris has a pKa value of 8.3, indicating that it is a weak base. However, since HCl is a strong acid, it will completely dissociate in water, resulting in a hydronium ion (H3O+) and a chloride ion (Cl-) in solution.
As a result, the concentration of hydronium ions will be twice that of the initial HCl concentration (0.1 M). On the other hand, the Tris concentration remains unchanged at 0.20 M.
Since the concentrations of the acidic and basic components of the solution are not approximately equal, this resulting solution is not a buffer solution. A buffer solution is typically prepared by mixing a weak acid and its conjugate base (or a weak base and its conjugate acid) in relative equal concentrations to effectively resist changes in pH.