Importance of Indicators

[Marc Farah 3D]

What is the key aspect we need to know about indicators in titration problems?

[Mikaela Gareeb 3G]

I think we need to know what they are (weak acids that change color when the stoichiometric point is reached), but when I asked Lavelle during office hours, he said that we don't need to know the colors.

[Preston_Dang_1B]

The main thing about indicators is that they cause the solution you are titrating to change color when you reach the stoichiometric point of a titration. There's a bunch of different indicators with different pK_ln values and you have to strategically select an indicator that has a pK_In value that is closest to the pH at the stoichiometric point of a titration. For example, titrating CH₃COOH with NaOH results in a pH of about 9 at the stoichiometric point. As a result, using a phenolphthalein indicator (turns from clear to a really pale pink at the stoichiometric point, but becomes really dark purple if you put too much base in) would be most effective in determining when you have added enough NaOH to complete the titration.