Textbook Question 6E.3

[Sebastian2I]

The solution manual specifies that because the Ka value for the second ionization is significantly lower than the first it can be ignored when calculating pH. What exactly is the threshold difference in values for this?

[Lilyana Villa 3L]

I'm not quite sure about the exact threshold of values, but I remember Dr. Lavelle in his office hours said that the only polyprotic acid that we should calculate the 2nd ionization for is sulfuric acid (since it's a strong acid), and for other polyprotic acids, we can ignore the 2nd ionization since Ka2 will be very small. Now I'm not sure if he meant just the polyprotic acids listed in the textbook or for any polyprotic acid (besides sulfuric acid) that we'll be given in this class.