I am completely stuck on the following question:
when phosphoric acid is titrated ith NaOH to pH 8.0, how many protons are "removed" from the phosphoric acid molecule? Which of the following indicators would you use to detect the endpoint?
Alizarin Yellow R 10.0 to 12.0
Phenolphthalein 8.0 to 10.0
Methyl Orange 3.1 to 4.4
Quinaldine Red 1.3 to 3.2
I know that phosphoric acid has 3 H+ ions to donate, however, I also know that it acts as a buffer around the phenolphthalein endpoint (8.2). If this acts as a buffer, and stabilizes the pH, does it actually transfer any H+? My guess is that it doesn't. Since the endpoint is 8.0, I am assuming that phenolphthalein is the correct indicator to use, however , I know that NaOH has a pKa of 3.06 and phosphoric acid has a pKa of 2.12, so should I be using quanaldine red which has a range of 1.3 to 3.2 to overcome the buffering capacity?