Question

The Western Diamondback Rattlesnake venom includes anticoagulant proteases that prevent fibrinogen from coagulating. It turns out there are four proteases in the venom, all with maximum proteolytic activity at pH =7. You are working on an anti-venom, and need to determine whether a pH of about 8 inactivates the proteases. (8 points) a) Please describe how you would prepare a buffer with a pH of 8.25 and a final concentration of 0.100 M. Be sure to identify the specific chemical you would use, and the number of moles of each chemical in your procedure. (Don’t worry about the number of grams of chemical you would need since you may not have the MW.)

Answer 1

To prepare a buffer, a compound with pKa near the pH to be maintained (less than 1 difference) should be used.

For this buffer, the HBrO is selected, with a pKa of 8.70.

The Henderson-Hasselbalch equation is used to determine the concentration ratio required by the HBrO Buffer and its NaBrO salt.

pH = pKa + Log [Salt] / [Acid]

We replace:

8.25 = 8.70 + Log [Salt] / [Acid]

[Salt] / [Acid] = 0.3548

According to the final concentration that the buffer must have:

[Salt] + [Acid] = 0.1 M

we cleared:

[Salt] = 0.1 - [Acid]

and we substitute in previous equation:

0.1 - [Acid] / [Acid] = 0.3548

We cleared:

[Acid] = 0.074 M

[Salt] = 0.1 - 0.074 = 0.026 M

We calculate the moles for 1000 mL of buffer:

n Acid = 0.074 moles

n Salt = 0.026 moles

0.074 moles of HBrO and 0.026 moles of NaBrO are required to prepare said buffer.