This is a topic that I simply know very little about. The question is asking me to determine the pKa value from the titration curves that I graphed in a recent experiment. Although I know the "buffer region," I have no idea how to determine the pKa. The weak base was 1M, 0.75M, 0.50M, and 0.25M of 30mL sodium carbonate and HCl was the strong acid added in increments of 1mL at a time, whereupon a pH was taken. Can anybody please help? I need as much help as I can get at this present time! Also, why doesn't the starting concentration of sodium carbonate affect the determination of the pKa? Is it because it's a base?