[alt-photo] Re: molarity problem

[Joseph Smigiel]

Thanks Eric, Alberto and Don for your replies.  Sorry for any  
confusion with the abbreviations.  I also see that the subscripts are  
not appearing as such in the posted version of my earlier message.   
Hope that isn't confusing anyone.

Joe


On Jul 24, 2010, at 10:17 AM, EJ Photo wrote:

> Joe, It is best to look at the compound as a unit and parts. It  
> might look
> like your mixing the abbreviations in your question which can also  
> leads
> problems, in some cases, it looks like mol = molecule and others  
> you are
> referring to a mole.
>
> there was a citing in an earlier post as to the magic number,  
> Avogadro's #
> of 6.022 x 10 the 23rd. that is a mole or number abbreviated mol  
> ( without .
> )
>
> molecule = mol. (with .)
>
> Just trying to help those following along. With all the different  
> email
> programs, etc . can jump around.
>
> http://www.cas.org/products/print/ca/standabbrevacro.html
>
>
> And Alberto pointed out, careful of rounding errors.
>
>
> Eric Neilsen
> Eric Neilsen Photography
> 4101 Commerce Street, Suite 9
> Dallas, TX 75226
>
> www.ericneilsenphotography.com
> skype me with ejprinter
> www.ericneilsenphotography.com/forum1
> Let's Talk Photography
>
>
> -----Original Message-----
> From: alt-photo-process-list-bounces at lists.altphotolist.org
> [mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On  
> Behalf Of
> Joseph Smigiel
> Sent: Friday, July 23, 2010 10:04 PM
> To: The alternative photographic processes mailing list
> Subject: [alt-photo] molarity problem
>
>
> On Jul 23, 2010, at 7:25 PM, Terry King wrote:
>
>>
>>
>> 'Molarity' has it's place ...
>
>
> OK.  Let me see if I have this straight using a different process.
> In wetplate collodion some of the commonly used salts are Cadmium
> Bromide (CdBr2) and Cadmium Iodide (CdI2).  I'd like to get away from
> using cadmium since it is so toxic and substitute something like
> Potassium Bromide (KBr) and Potassium Iodide (KI) salts.  The halogen
> combines with the silver in the Silver Nitrate (AgNO3) sensitizing
> bath to form Silver Bromide (AgBr) and Silver Iodide (AgI) and
> therefore the proper balance of halogen salts is important.
>
> So, to maintain proper halogen content when substituting the metals,
> I'd need to know the following:
>
> KBr is 119 gm/mol
>
> KI is 166 gm/mol
> CdBr2 is 272 gm/mol
>
> CdI2 is 366 gm/mol
>
>
>
> There would be 2 mol Potassium and 2 mol Bromide in 2 gm KBr.
>
> There would be 1 mol Cadmium and 2 mol Bromide in 2 gm CdBr2.  (is
> that 1:2 mol ratio correct for the compound?)
>
> Then, if I have:
>
> 2 gm KBr  * (1 mol KBr /119 gm KBr) ~ 0.0168 mol KBr
>
> and
>
> 0.0168 mol KBr * (1 mol Br/ 1 mol KBr) * (1 mol CdBr2 / 2 mol Br) *
> (272 gm CdBr2/ 1 mol CdBr2) ~ 2.285 gm CdBr2
>
> 2 gm KBr would contain as much bromide as 2.285 gm CdBr2.
>
> Therefore the substitution would be ~ 1 gm KBr / 1.14 gm CdBr2.
> (Similarly, the substitution between KI and CdI2 would be ~1 gm KI /
> 1.10 gm CdI2.)
>
> If a formula called for 1.0 gm CdBr2, I would need to substitute ~
> 0.88 gm KBr.
>
>
> Could a chemist on the list verify the above for me?  Thanks.
>
> Joe
>
>
> p.s.,  Since KBr is essentially insoluble in alcohol or ether, and
> collodion deteriorates with very little water content, and the grain
> alcohol used already has 5% water content, making percentage salt
> solutions for this process doesn't make sense.  At least I don't see
> where it would be helpful.
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