1. The problem statement, all variables and given/known data What is the concentration of acetic acid in 250mL of a 100mM acetate buffer at pH 4.76? 2. Relevant equations Henderson Hasselback 3. The attempt at a solution I used the Henderson Hasselback equation. plugged in 4.76 for pKa. plugged in .025 for the concentration of A-. plugged in 4.76 for pH. Solved and got 25mM. The answer is supposed to be 50mM. Would appreciate the help, thanks.