Question

Tris-HCI in solution will produce a pH of approximately 4.7 and Tris-Base in solution will produce a pH of approximately 10.4. Which one has the better buffering capacity?

Answer 1

Buffer capacity quantifies the ability of a solution to resist changes in pH by either absorbing or desorbing H⁺ and OH^- ions. When an acid or base is added to a buffer system, the effect on pH change can be large or small, depending on both the initial pH and the capacity of the buffer to resist change in pH.

Tris base (molecular weight: 121.14 g/mol) is base, and Tris-HCl (Tris base which is already combined with HCl in a 1:1 molar ratio, so the molecular weight is 157.6 g/mol).

pKa for TRIS : 8.1

If the pH of solution is greater than the pKa, the group is in the conjugate base form (deprotonated). If the pH of solution is less than the pKa, the group is in the conjugate acid form (protonated).

Buffer Solution with pH near to pKa have better buffering capacity , than solution with greater difference in pH and pKa . Thus, Tris-Base in solution which will produce a pH of approximately 10.4 ( closer to pKa - 8.1) better buffering capacity than Tris-HCI in solution which will produce a pH of approximately 4.7.