Problem 6E.3 - part b

[Rhea McKenzie 2J]

I've solved part b of this problem multiple times and keep getting pH = 2.11. However, the answer key states that the pH should equal 1.28. Can someone please confirm which answer is correct for me?

6E.3
Calculate the pH of each of the following solutions of diprotic acids at 25 °C, ignoring second deprotonations only when the approximation is justified:
(b) 0.10M (COOH)2

Here is a pic of my work:

[Chem_Mod]

You used the wrong Ka's.

[Justine Lim 3L]

Hi! I believe you may have used the wrong Ka value. Table 6E.1 shows that the Ka1 for (COOH)2 is 5.9*10^-2, but it seems like you used the Ka1 value for C2H4O2(COOH)2 instead. Hope this helps :)

[Rhea McKenzie 2J]

Oh perfect, thank you so much!