The Conjugate Seesaw

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Annah Khan 1B
Posts: 28
Joined: Fri Jul 22, 2016 3:00 am


Postby Annah Khan 1B » Sun Jul 30, 2017 2:35 pm

"Which is the stronger base, the hypobromite ion, BrO-, or morphine, C17H19O3N? Justify your answer."

I understand what the problem is asking, but I'm not entirely sure how to find the answer. Could someone explain this to me please? Thanks!

Posts: 20
Joined: Fri Jul 22, 2016 3:00 am

Re: 12.49

Postby 404768057 » Sun Jul 30, 2017 6:35 pm

Hypobromite ion is the conjugate base of hypobromous acid. From the table 12.1, the pKa of hypobromous acid is 8.69. We know that pKa+pKb=14. To get pKb, take 8.69 from 14 and you get 5.31. From table 12.2, we know that the pKb for C17H19O3N is 5.79.The pKb of hypobromite is smaller, which means that the base is stronger.

Leah Savage 2F
Posts: 74
Joined: Fri Sep 29, 2017 7:06 am

Re: 12.49

Postby Leah Savage 2F » Mon Dec 04, 2017 11:40 pm

Would we be expected to know this without having the pkb or pka or kb or ka provided? There are a lot of problems where you have to order strength of acids/bases. I know there are rules for binary acids and oxoacids, but what about for a problem like this one?

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Joined: Fri Sep 29, 2017 7:07 am

Re: 12.49

Postby Cooper1C » Wed Dec 06, 2017 11:43 am

Is there any way to figure out this problem by looking at the Lewis structures?

Michelle Steinberg2J
Posts: 73
Joined: Fri Sep 29, 2017 7:04 am

Re: 12.49

Postby Michelle Steinberg2J » Wed Dec 06, 2017 9:16 pm

I have the same question! I'm assuming we will be provided with the necessary pKa and pKb values?

Diego Zavala 2I
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Re: 12.49

Postby Diego Zavala 2I » Thu Dec 07, 2017 1:03 pm

You can predict that BrO- will be the stronger base. Because morphine has a N with a lone pair of electrons, H+ will bind to the nitrogen resulting in a very weak base. HBrO is a weak acid so its conjugate base BrO- will be relatively stronger.

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