[eml-dev] [Fwd: Re: EML units - pH]

[Dan Higgins]

Hi All,
    As I learned it, a mole (of anything) is not a mass (grams). It is a 
_count _in units of Avagado's number (6.023x10^23) Or, as defined by NIST

The mole is the amount of substance of a system which contains as many 
elementary entities as there are atoms in 0.012 kilogram of carbon 12

It thus really has no units.

Dan

----

Matt Jones wrote:

>
> ------------------------------------------------------------------------
>
> Subject:
> Re: EML units - pH
> From:
> Matt Jones <jones at nceas.ucsb.edu>
> Date:
> Mon, 04 Apr 2005 10:46:18 -0800
> To:
> David Balsiger <dbalsiger at wisc.edu>
>
> To:
> David Balsiger <dbalsiger at wisc.edu>
> CC:
> servilla at lternet.edu, sheldon at uga.edu, bjbenson at wisc.edu, 
> pmkapadia at wisc.edu
>
>
> This is a tricky one that we discussed a lot in the eml group but were 
> ultimately stymied.  Here's the basics as I recall it:
>
> pH = -log(moles H/liter)
>
> moles H =~ grams because the molecular weight of H is 1
>
> thus,
>
> pH =~ -log(grams H/liter)
>
> For example, for a solution with hydrogen ion concentration of 10^−4, 
> or 0.0001, moles per liter, the pH is 4.
>
> The problem we run into is how to deal with the -log, which doesn't 
> really change the units.  STMML doesn't really deal with 
> transformations like this, so we weren't really sure how to either.  
> The unit seems like it should be -log(moles/l) [or for hydrogen maybe 
> -log(grams/liter)], but we didn't really know what to make of it 
> because STMML has no way to express functions such as logarithms as 
> far as we could tell.  Its possible that transformaitons like this 
> make the value dimensionless, but I'm not sure.  This problem extends 
> beyond pH to other similar transformations such as sin, cos, etc., but 
> pH seems a very common case. STMML probably would need to be extended 
> with a general purpose expression language that supports common 
> transformation functions to really define pH.  Suggestions are welcome 
> on how to handle this in the EML units description.
>
> Matt
>
> David Balsiger wrote:
>
>> Matt, Mark, Wade,
>>
>> Surely someone has determined the correct unit and unit/type 
>> descriptions for standard pH measurements. Can you save us some time 
>> and effort in this matter?
>>
>> Thanks
>> Dave
>>
>>
>> Dave Balsiger   Center for Limnology  265-7944
>
>
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>


-- 
*******************************************************************
Dan Higgins                                  higgins at nceas.ucsb.edu
http://www.nceas.ucsb.edu/    Ph: 805-893-5127
National Center for Ecological Analysis and Synthesis (NCEAS) 
Marine Science Building - Room 3405
Santa Barbara, CA 93195
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