Textbook Problem 6D.15 Part B

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Samantha Pedersen 2K
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Textbook Problem 6D.15 Part B

Postby Samantha Pedersen 2K » Sat Jan 16, 2021 11:23 am

Part B of problem 6D.15 asks us to calculate the pH of 0.055 M AlCl3 (aq), and we have to use Table 6C.1 and Table 6C.2 to determine the Ka value to use in the calculation. However, I don't see a Ka value or a Kb value of the conjugate base that could be used to determine the Ka value in either of these tables. For anyone who has done this problem, how did you figure out what the Ka value is? Thank you!

Zaid Bustami 1B
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Re: Textbook Problem 6D.15 Part B

Postby Zaid Bustami 1B » Sat Jan 16, 2021 3:33 pm

Hey Samantha!

For this problem you'd actually need to refer to table 6D.1 in chapter 6D of the textbook. I know the problem doesn't say it, but tables 6C.1 and 6C.2 don't contain any information on those highly charged cations that we know produce acidic solutions. Table 6D.1 lists the Ka for Al(H2O)63+, and you'd use that to solve your ICE box equation, for which the ionization reaction is:
Al(H2O)63+ + H2O ⇌ Al(H2O)5OH2+ + H3O+

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