Question 6E.3 7th edition

[ConnorRazmaDis2I]

The question states "ignoring second deprotonations only when the approximation is justified. How do we know when its justified?

[aisteles1G]

When the difference in Ka1 and Ka2 values is over 10^3 you can ignore the second Ka and just use the one for ka1 but if its like ka1= 1*10^-2 and ka2=1*10^-3 then you have to use the second K value and can't ignore it. Hope this helps! It talks about this in the 6E chapter in the textbook

[Chem_Mod]

The book states that the second deprotonation will always occur, but so long as the provided Ka₂ is less than about Ka₁/1000 then the second deprotonation will be so small that it will not affect the pH significantly and can thus be ignored.