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kclive

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question about concentration
« on: October 07, 2005, 09:55:22 PM »
0.25 M CH3OH: find the concentrations of each ion or molecule present in the solution.

:please:

Since (in my knowledge), CH3OH does not dissociate in solution, this must be the final solution to the problem. How do you do this?!! :swear: All help is appreciated.

-kclive


Offline mike

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Re:question about concentration
« Reply #1 on: October 07, 2005, 10:05:20 PM »
YEs sounds right concentration of CH3OH is 0.25M.

Unless you know K or pKa and it is forming the CH3O- ion? doubt it though, strange question huh?
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Offline Borek

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Re:question about concentration
« Reply #2 on: October 08, 2005, 11:50:33 AM »
Ka of methanol is too low for CH3OH dissociation to be of any concern here, however, don't forget about water autodissociation.
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kclive

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Re:question about concentration
« Reply #3 on: October 08, 2005, 09:56:38 PM »
What do you by K, Ka, and pKa of CH3OH? Seems like I will be learning this later this year. But can you please simply tell me how CH3OH dissociates without using any super-advanced science terms?:aak:

But you said there is a such thing as a CH3O- ion. It's probably not on my humongous ion chart I have here. So that means that CH3OH will dissociate into CH3O- and H+ ions in solution. Voila!
:D

Thanks for all of your help.

-kclive

:cool1:

« Last Edit: October 08, 2005, 10:01:23 PM by kclive »

Garneck

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Re:question about concentration
« Reply #4 on: October 09, 2005, 05:41:25 AM »
pKa for methanol is somewhat close to water and is exactly 15.2.. so there will be ions in the solution through dissociation..  

Offline Borek

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Re:question about concentration
« Reply #5 on: October 09, 2005, 06:34:12 AM »
pKa for methanol is somewhat close to water and is exactly 15.2.. so there will be ions in the solution through dissociation..  

Can you give reference? I remembered it as about 17, but I could be wrong and I can't locate it in my books at the moment (although I am almost sure it is less then 10 feets from me ;) )
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Garneck

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Re:question about concentration
« Reply #6 on: October 09, 2005, 10:06:45 AM »
15.2 is in a table I have at home

I found a table on google, and it says 15.5 in it. Click here.

Karakth

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Re:question about concentration
« Reply #7 on: October 10, 2005, 04:06:35 PM »
If they haven't yet learned about Ka etc then I don't think they'd be asked to find how methaol and water dissociate to form the three ions.

I don't suppose it's an easy calculation, although I might be wrong. My initial reserverations come from the fact that the H+ ion would be shared and change the Ka for both of them...Am I wrong in this?

Offline Borek

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Re:question about concentration
« Reply #8 on: October 10, 2005, 04:34:18 PM »
I don't suppose it's an easy calculation, although I might be wrong. My initial reserverations come from the fact that the H+ ion would be shared and change the Ka for both of them...Am I wrong in this?

No, it is not trivial calculation. And yes, you are wrong - Ka will be not changed ;)

However, I will be not surprised if the correct (expected) answer will be H2O, CH3OH and water dissociation products (H+ and OH-). Water ionization is covered together with pH, so not very late in the chemistry course.
« Last Edit: October 10, 2005, 05:29:54 PM by Borek »
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