The correct answer is to measure the pH of the "made up" buffer, then add acid or base as appropriate to reach the desired pH.
If this is a problem, look at the pka for HEPES, and add acid or base as appropriate to get to 8.
Do you add Nacl or HCL if your target buffer pH is 8, and the buffer is HEPES
2 answers
Dr. Bob222 is correct, you will need to add base to increase the pH of HEPES to 8, since the pKA of the solution is at 7.5. Remember, buffers have equal concentrations of its acid and conjugate base. Therefore, the pH of the solution is equal to the pKa.