Textbook Problem 6E.3

[Samantha Pedersen 2K]

Problem 6E.3 from the textbook says, "Calculate the pH of each of the following solutions of diprotic acids at 25 °C, ignoring second deprotonations only when the approximation is justified." For each part of the question, the solutions manual says, "Because Ka2 << Ka1, the second ionization can be ignored." What is the cutoff for when the second ionization can be ignored? Thank you!

[HilaGelfer_2H]

Hi!

I think the cut off is like any other weak acid where Ka < 10^-4.

I hope this helps :)

[Yu Jin Kwon 3L]

Just for clarification, the reason why the cut off is Ka < 10^-4 (rather than the usual < 10^-3) is because Dr. Lavelle wanted us to be extra careful when using 10^-3 as a cut off because something could be a very large number multiplied with 10^-3, which would make it closer to 10^-2 than 10^-4 :)! You can also check your approximations using the percent ionization check and make sure it's less than 5% :)!