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

by BThomas1219
Tags: acid, added, determine, propionic, volume
 P: 3 1. The problem statement, all variables and given/known data Given 250ml of 0.1M HC3H5O2 (Ka=1.35E-5) What volume of a)1.0M HCl is needed to lower the pH to 1.00. b) 1.00M NaC3H5O2 raise pH to 4.00 2. Relevant equations pH=pKa-log (HA/A) ICE chart 3. The attempt at a solution I used the ice chart for the dissociation of propionic acid. I determined the concentration of H+ and A- to be 1.16E-3. the pH was 2.93. I do not know how to factor in the HCl to determine the volume needed to lower the pH.
 Admin P: 21,722 $$K_a = \frac {[A^-][H^+]}{[HA]}$$ 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.

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