Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Calculating % ionization given pKa and pH of solution?
I'm trying to calculate the % ionization of the carboxylic acid R group in aspirin given a pKa of 3.5 and a pH of 7.4.
I'm very confused about how to apply the Henderson Hasselbalch equation in this context and how to get the concentration of the conjugate acid and base. Any help would be greatly appreciated.
2 Answers
- 1 decade agoFavorite Answer
10 to the negative pH value will give you the concentration of the ions in the solution of the acid. This is how much it has dissociated by. This over the original concentration of the acid times 100 will give you a %. If you don't have the original concentration, then substitute x in the Ka expression and solve for it.
Source(s): Just did this section in chemistry - Anonymous5 years ago
AH + H2O ==== A- + H3O+ (monoprotic acids) Ka = (A-)(H3O+) / (AH)(H2O), this is showing activities of compounds, translating into concentrations, Ka = [A-] [H+]/[AH] pKa = -log Ka = log {[AH]/[A-]} - log [H+] = log [AH] - log [A-] - log [H+] Balance of mass a-x ---- x + x, in equilibrium, so [H+] = [A-], and knowing -log [H+] = pH pKa = log {[AH]o - [H+]} + 2 pH [H+] = 10^-3.4 = 3.98 * 10^-4 pKa = log (0.25 - 3.98*10^-4) + 6.8 = 6.197 Ka = 6.35 * 10^-7
