HW 12.45

Moderators: Chem_Mod, Chem_Admin

nanditasundarapandian1D
Posts: 21
Joined: Sat Jul 22, 2017 3:01 am

HW 12.45

Postby nanditasundarapandian1D » Wed Dec 06, 2017 5:37 pm

Arrange the following bases in order of increasing strength on the basis of the pKa values of their conjugate acids, which are given in parentheses: (a) ammonia (9.26);
(b) methylamine (10.56); (c) ethylamine (10.81); (d) aniline (4.63) (see Exercise 12.44). Is there a simple pattern of strengths?


I know that the relationship between acids/bases and their conjugates is that the stronger the acid/base was the weaker its conjugate is. But I don't know where to go from that?

Naveed Zaman 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am
Been upvoted: 2 times

Re: HW 12.45

Postby Naveed Zaman 1C » Wed Dec 06, 2017 7:16 pm

Strong bases have weak conjugate acids, and weak bases have strong conjugate acids. A weak conjugate acid will also have a high pKa value (pKa = 10 is more acidic than pKa = 12 because you're talking about an [H+] concentration of 1 x 10-10M vs. 1 x 10-12M). So if the pKa value is high, then the base is strong.

Christina Cen 2J
Posts: 53
Joined: Sat Jul 22, 2017 3:01 am

Re: HW 12.45

Postby Christina Cen 2J » Thu Dec 07, 2017 7:00 pm

pkb = 14 - pka
The lower the pkb is, the stronger the base, so the higher the pka = smaller pkb = stronger base

Wenjie Dong 2E
Posts: 53
Joined: Fri Jun 23, 2017 11:40 am

Re: HW 12.45

Postby Wenjie Dong 2E » Thu Dec 07, 2017 7:59 pm

Christina Cen 3E wrote:pkb = 14 - pka
The lower the pkb is, the stronger the base, so the higher the pka = smaller pkb = stronger base

I agree with your explanation!

Phillip Winters 2F
Posts: 50
Joined: Fri Sep 29, 2017 7:05 am

Re: HW 12.45

Postby Phillip Winters 2F » Fri Dec 08, 2017 9:12 am

If an acid has a low pKa, that means that it is a strong acid, and thus it has a weak conjugate base, and thus acids with high pKa's have strong conjugate bases


Return to “Conjugate Acids & Bases”

Who is online

Users browsing this forum: No registered users and 1 guest