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Topic: find the ratio of the concentrations of the salicylate ion  (Read 5767 times)

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lena

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find the ratio of the concentrations of the salicylate ion
« on: December 05, 2004, 01:21:57 PM »
I stuck with problem! Please *delete me*
Aspirin is a derivative of salicylic acid, which has a Ka = 1.1*10-3.
Calculate the ratio of the concentrations of the salicylate ion (conjugate base) to salicylic acid in a solution that has a pH adjusted to 2.50 by using strong acid or strong base
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Offline Mitch

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #1 on: December 05, 2004, 03:07:46 PM »
You have to attempt the problem.
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lena

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #2 on: December 05, 2004, 03:57:05 PM »
 ???I do not have any idea how to start.
Thank you.
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Offline Donaldson Tan

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #3 on: December 05, 2004, 04:24:09 PM »
this is a buffer pH question.

Given an acid HA dissociates in the following manner:

HA <-> H+ + A-

Ka = [H+][A-]/[HA]

your job is to find [A-]/[HA]
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lena

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #4 on: December 05, 2004, 05:52:41 PM »
Thanks a lot!!! I think I got it!!!! :)
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lena

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #5 on: December 05, 2004, 08:06:12 PM »
Is it correct?
PH = 2.50 [H3O+]= antilog –2.50 = 3.16 * 10^-3M
Ratio = Ka/[H3O+] Ratio = 1.1* 10^-3/3.16 * 10^-3 =
.348
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Offline Donaldson Tan

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Re:find the ratio of the concentrations of the salicylate ion
« Reply #6 on: December 05, 2004, 08:38:14 PM »
yes

I would use the following method:

Ka = [H+][A-]/[HA]

pKa = pH - lg [A-]/[HA]

lg [A-]/[HA] = pH - pKa
« Last Edit: December 05, 2004, 09:38:59 PM by geodome »
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"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006
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