When is second deprotonation of a polyprotic acid ignored?

[shonanchiang2L]

In the syllabus textbook problem 6E.3, the problem tells you to calculate pH of a given quantity of a polyprotic acid and tells you to ignore the second deprotonation "only when that approximation is justified." The answer key for this problem explains that when Ka2 << Ka1, the second ionization can be ignored. Mathematically, though what is considered "much less than?" Does the difference between Ka2 and Ka1 have to be greater than 10^3? What is the number threshold? Thank you!

[Shail Patel 3A]

Within the chapter overview, Dr. Lavelle includes a sub-note stating: "Subsequent deprotonations do take place but provided KA2 is less than about KA1/1000, they do not affect the pH significantly and can be ignored". Hopefully, this helps!

[Hedy Bian 3H]

With the exception of H2SO4, the second deprotonation of a polyprotic or diprotic acid is typically ignored.