RE: [Histonet] ?Osmolarity

From:"Smith, Allen"

Osmolarity = molarity X number of ions per mole

In the case of phosphate buffered saline, there are 3 components, and you
have to calculate the osmolarity of each component and add the osmolarities
of the components to get the osmolarity of the solution.

The osmolarity of monobasic sodium phosphate is 2 X its molarity because the
hydrogens hardly dissociate.
The osmolarity of dibasic sodium phosphate is 3 X its molarity because both
sodiums fully dissociate, but the hydrogen doesn't.
The osmolarity of the saline is 2 X molarity of sodium chloride
Add all of the above to get the osmolarity of the solution.

Allen A. Smith, Ph.D.
Professor of Anatomy
Barry University
School of Graduate Medical Sciences
            Podiatric Medicine and Surgery
Miami Shores, Florida

-----Original Message-----
[] On Behalf Of Etheridge,
Sandra AGF:EX
Sent: Wednesday, July 07, 2004 4:21 PM
To: (
Subject: [Histonet] ?Osmolarity

Hello, everyone,

I was asked today by a fellow co-worker if I knew what osmolarity was and
how to calculate it for a complex solution.  She needs to find the
osmolarity of a Phosphate Buffered Saline solution (made inhouse).  She has
the normal concentrations for all the components, but doesn't know where to
go from there, and neither do I!!!!

Any help or info is, as always, appreciated.

Sandra Etheridge
Animal Health Center
BC Ministry of Agriculture, Food & Fisheries
Abbotsford, BC
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