Asked by nicki
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?
Answers
Answered by
DrBob222
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
(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
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