# Determine volume of HCl added to propionic acid to get pH=1

by BThomas1219
Tags: acid, added, determine, propionic, volume
 Admin P: 23,363 $$K_a = \frac {[A^-][H^+]}{[HA]}$$ rearranged: $$\frac {[A^-]}{[HA]} = 10^{pH - pK_a}$$ At pH 1.0 only about 101-4.75=10-3.75=2x10-4 of the acetic acid is dissociated. That means in the first case you can - more or less safely - assume presence of acetic acid doesn't matter much, as the first approximation pH will depend mostly on the HCl dilution. Second case is just a buffer solution, use Henderson-Hasselbalch equation.