Question on 12.41

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Joanna Pham - 2D
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Joined: Fri Apr 06, 2018 11:04 am

Question on 12.41

Postby Joanna Pham - 2D » Tue Jan 15, 2019 9:12 am

For this question, it says to use tables 12.1 and 12.2 to place the bases in order of increasing strength: F-, NH3, CH3CO2-, and C5H5N.

Only C5H5N is present on the tables. How do I determine which base is stronger and weaker (F-, NH3, and CH3CO2-)?

Charles Hood Disc 1C
Posts: 39
Joined: Fri Sep 28, 2018 12:19 am

Re: Question on 12.41

Postby Charles Hood Disc 1C » Tue Jan 15, 2019 9:54 am

The others are acids, not bases so they can be found in table 12.1, except bonded to another element (generally hydrogen) this gives you the Ka value instead of the Kb value. This means that you can can subtract the pKa from 14 to find the pKb.

Ethan Baurle 1A
Posts: 33
Joined: Fri Sep 28, 2018 12:19 am

Re: Question on 12.41

Postby Ethan Baurle 1A » Tue Jan 15, 2019 11:00 am

Also, in regards to the strengths of acids and bases based on their equilibrium constants, a lower Kx (Ka or Kb) shows a weaker substance. A lower Kx also responds to a higher PKx if those are the values you are looking at, so a higher PKx would be weaker.

A De Castro 14B 2H
Posts: 75
Joined: Fri Sep 28, 2018 12:29 am

Re: Question on 12.41

Postby A De Castro 14B 2H » Tue Jan 15, 2019 2:41 pm

I believe both C5H5N and NH3 are in table 12.2. As for the anions, you can find their pKb values by subtracting the pKa values of their parent acids (HF and CH3COOH), found in table 12.1, from 14 (which is pKw). The lower the pKb value, the stronger the base is.

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