Propanoic Acid, HC3H5O2, is a weak acid. A 0.125 M solution of propanoic acid, H
ID: 598641 • Letter: P
Question
Propanoic Acid, HC3H5O2, is a weak acid. A 0.125 M solution of propanoic acid, HC3H5O2, dissociates 1.020%. Using this information, calculate the pH of the 0.125 M solution of propanoic acid.Calculate the pH of the 0.125 M solution of propanoic acid.
Explanation / Answer
Acetic acid ionizes partially, so you need the pka or ka value of acetic acid (in data book), this should be given in the question. SO YOU NEED TO CALCULATE THE CONCENTRATION OF H+ (OR H3O+) Calculation CH3COOH(aq) + H2O(l) -----> CH3COO-(aq) + H3O+(aq) Ka IS DISSOCIATION CONSTANT WHICH IS CONCENTRATION OF PRODUCT/CONCENTRATION OF REACTANT. Ka= [CH3COO-] * [H3O+] / [CH3COOH] [H2O] is not included because its change in concentration is negligible. After partial dissociation, [CH3COOH] IS STILL APPROXIMATELY 0.1M. [CH3COO-] = [H3O+] Ka of CH3COOH=1.74 * 10^-5 (from data book) 1.74 * 10^-5 = [H30+]^2 / 0.1 [H30]^2 = 1.74*10^-5 * 0.1 = 1.74*10^-6 [H30+]= 1.32*10^-3 pH= -log[H30+] pH= -log(1.32*10^-3) pH= 2.88 pH of 0.1M acetic acid is 2.88
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