Phthalic acid H2C8H4O4 is a diprotic acid. It is used to make phenolphthalein in
ID: 718542 • Letter: P
Question
Phthalic acid H2C8H4O4 is a diprotic acid. It is used to make phenolphthalein indicator. Kal= 0.0012 and Ka2 = 3.9 x 10^-6. Calculate the pH of a 2.9 M solution of phthalic acid. Estimate [HC8H4O4^-] and [C6H6O6^2-]
Please help with showing exactly how you get the answer, I am very confused on this so formulas etc really help!
Explanation / Answer
Step 1: Ionic Equation H2C8H4O4 ----------->HC8H4O4^- + H+ We can neglect Ka2 because it is very least. Step 2: Draw ICE Table. Initial Concentration 2.9M 0 0 Changing Concentration - X +X +X Equilibrium Concentration (2.9-X)M +X +X Ka1 = X^2/(2.9-X) 0.0012 = X^2/(2.9-X) The Equilibrium Constant is [H+] = 0.0584 M pH = -log [H+] = -log (0.0584) pH = 1.23 The pH of 2.9 M Phthalic acid H2C8H4O4, is a diprotic acid, 1.23