polyprotic acids

[Savannah Mance 4G]

In 6E. for #1 the H2SO4 in its second protonation for the ICE table it's supposed to have a concentration of 0.15 for H3O+ the same as the H2SO4 initial concentration. But for #3 when H2CO3 is protonated, the H3O+ concentration is not 0.01 like the initial of H2CO3. I was wondering what made them different and whether it was because H2SO4 is a stronger acid.

[Amy Pham 1D]

You are correct. Although carbonic acid is a polyprotic acid, it is not strong, so even the first protonation will not result in the same H3O+ concentration as the initial carbonic acid concentration. On the other hand, H2SO4 is the stronger acid and will dissociate.

[Emma Popescu 1L]

H2SO4 is the only strong polyprotic acid and it is the most common for which deprotonation can be complete. The second deprotonation adds to H3O+ concentration so the overall pH of the solution is slightly lower due to first deprotonation alone. All the other polyprotic acids should be treated as weak monoprotic acids since the subsequent deprotonations do not affect the pH significantly so they are ignored.