Online Practice Question [ENDORSED]

[Madison_Newberry_3L]

Hi, I have been trying practice problems that I found online for working with polyprotic acids and bases, and I have stumbled upon this one problem that I cannot seem to figure out where the final answer came from and why. I understand upto solving for Ka1 and Ka2, however, I do not understand why that leads us to the determination that [CO^2-] is considered to be equal to 4.7 *10^-11 M.

[Chem_Mod]

Need to see the full question and answer to be able to comment. Or stop by one of the many drop in sessions or office hours to discuss and get assistance.

[Madison_Newberry_3L]

Sorry, for some reason the image of my work did not upload, but here is the full question