1. The problem statement, all variables and given/known data What volume of 0.200M HCl must be added to 250.0ml of 0.300M sodium mandelate to produce a buffer solution with a pH of 3.37? 2. Relevant equations 3. The attempt at a solution For 2 and 3, can I use the equation pH = pKa + log [A-/HA]? but for HCl isn't that 100% disassociation? How can we use that if the Ka is not a given value for HCl? Thanks.