Question

Tris {(hoch2)3cnh2} is one of the most common buffers used in biochemistry. a solution is prepared by adding enough tris and 12 m hcl(aq) to give 1.00 l of solution with [tris] = 0.30 m and [trish+] = 0.60 m. what is the ph of this buffered system if the pkb is 5.92?

Answer 1

Given:

Buffer system : Tris/TrisH+

[Tris] = 0.30 M

[TrisH+] = 0.60 M

pKb = 5.92

To determine:

pH of the buffer

Explanation:

The pH of a buffer can be obtain using the Henderson-Hasselbalch equation:

pH = pKa + log[Base]/[Acid]

In this case the conjugate base = [Tris]

Acid = [TrisH+]

Now, pKa = 14-pKa = 14-5.92 = 8.08

pH = 8.08 + log[0.30]/[0.60] = 7.778

Ans: pH of the buffer = 7.78

Answer 2

Given that,

The concentration of TRIS = 0.30 M

The concentration of TRIS+ = 0.60 M

Kb = 1.2 x 10^-6

pKb = -log Kb = - log (1.2 x 10^-6) = 5.920

Now, by using the Hendersonn equation,

pH = pKa + log TRIS+/TRIS = 5.920 + log (0.60/0.30) = 6.221

pOH=14-pH=14-6.221 = 7.779