1. The problem statement, all variables and given/known data Using sodium citrate and citric acid, create a buffer solution that will withstand an addition of 20ml of 0.1mol/L HCl or NaOH solution without a significant increase in pH (+/-2). Bonus marks for using the smallest amount of buffer solution. 2. Relevant equations Reaction: H3C6H5O7 ↔ 3H+ + C6H5O73- ka of Acetic Acid = 7.4x10-4 pka of Acetic Acid = 3.13 ph = pka + log[A-/HA] 3. The attempt at a solution I'm not sure where to begin. The Henderson-Hasselbalch equation above might be needed, but our teacher never showed us it, so most likely we have to create this solution without it. My understanding is that a solution needs to be created with the same concentration of hydronium ions from the citric acid as with the concentration of citrate, the conjugate base. Also, citric acid apparently is triprotic, losing 3 hydrogens in water. However, it is a weak acid, meaning it does not ionize completely. What is my first step in solving this overall question? Update: I used the H-H equation after receiving info that the pka and pH in buffer solutions must be equal. Making the two equal, I calculated that the concentration of acid divided by the concentration of its conjugate base must equal 1. How can I do this step in the lab? How do I make the ratio equal to 1?