Textbook Problem 6E.3

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Samantha Pedersen 2K
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Textbook Problem 6E.3

Postby Samantha Pedersen 2K » Sat Jan 16, 2021 2:20 pm

Problem 6E.3 from the textbook says, "Calculate the pH of each of the following solutions of diprotic acids at 25 °C, ignoring second deprotonations only when the approximation is justified." For each part of the question, the solutions manual says, "Because Ka2 << Ka1, the second ionization can be ignored." What is the cutoff for when the second ionization can be ignored? Thank you!

HilaGelfer_2H
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Re: Textbook Problem 6E.3

Postby HilaGelfer_2H » Sat Jan 16, 2021 2:47 pm

Hi!

I think the cut off is like any other weak acid where Ka < 10^-4.

I hope this helps :)

Yu Jin Kwon 3L
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Re: Textbook Problem 6E.3

Postby Yu Jin Kwon 3L » Sat Jan 16, 2021 8:52 pm

Just for clarification, the reason why the cut off is Ka < 10^-4 (rather than the usual < 10^-3) is because Dr. Lavelle wanted us to be extra careful when using 10^-3 as a cut off because something could be a very large number multiplied with 10^-3, which would make it closer to 10^-2 than 10^-4 :)! You can also check your approximations using the percent ionization check and make sure it's less than 5% :)!


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