6E.3 - Ignoring Second Deprotonation?

[Maria George 3K]

Textbook Question 6E.3 asks us to find the pH of diprotic acids in solution, saying "Calculate the pH of each of the following solutions of diprotic acids at 25 °C, ignoring second deprotonations only when the approximation is justified"

What is an example of a justified approximation for this? When can we ignore second deprotonation?

[Tala Hamdan 3B]

In almost all cases, (except for H2SO4) we would assume the Ka value of the second protonation reaction to be very small, meaning that it is insignificant and will not have a noticeable effect on the pH of the solution.