molarity of HCl

[David F. Spencer]

In article <62niqp$pev at usenet.srv.cis.pitt.edu>,
mihalek at NOSPAM.smtp.anes.upmc.edu (Robert M. Mihalek) wrote:

> In article <344B8865.41C6 at physik.mu-luebeck.de>
> Thomas Hettmann <hettmann at physik.mu-luebeck.de> writes:
> 
> > Let's start with the 37%. If nothing else is specified, that means
> > weight per weight, i.e. 370 g of HCl per 1 kg of solution.
> 
> Is weight per weight really the default unit?  I was under the
> impression, though I've never read the official rules anywhere, that
> weight per volume was the default unit. Most replies to this post seem
> to believe that 37% specifies weight per volume, not weight per weight.

Concentrated hydrochloric acid is approximately 37 weight percent (37%
weight/weight) which is why the density of the solution is critical to
determining the molarity (moles/litre). This seems to be the standard way
of designating the stock concentrations of inorganic acids (phosphoric
acid, nitric, hydrobromic, perchloric, etc. are all sold by weight %). 
Formaldehyde and ammonium hydroxide are also sold as weight per cent
solutions. 

Dave

--------------------------------------------
David F. Spencer, PhD
Dept. Of Biochemistry
Dalhousie University
Halifax, Nova Scotia
Canada

dspencer at is.dal.ca
dspencer at rsu.biochem.dal.ca