What is a "degree Baumé"?

I work at a water park, and our 55 gallon HCl barrels come labeled as having a concentration of 22 degrees Baumé. I would like to know what the conversion factor is from "degrees Baumeé" to Molar?

 Vocabulary Baumé scale hydrometer mass percentage specific gravity

The Baumé scale is a measure of a solution's specific gravity, not its concentration. To get the molarity of the HCl, you'll have to convert degrees Baumé to a specific gravity, and then use the specific gravity to look up the concentration of HCl from a table in a handbook. For example, the CRC handbook has tables that relate specific gravities to concentrations for sulfuric acid.

 Pure water 15 (w/w)% NaCl Calibration of a heavier-than-waterhydrometer on the Baumé scale.
The French chemist Antoine Baumé devised the scale for marking hydrometers. For liquids that are heavier than water, 0°Bé marks the water level of the hydrometer placed in pure water, and 15°Bé corresponds to the water level when the scale is placed in a solution that is 15% NaCl by mass. For liquids that are lighter than water, 10°Bé marks the level for pure water and 0°Bé corresponds to a solution that is 10% NaCl by mass.

At 60°F, specific gravity can be calculated from degrees Baumé using the following formulas:

 liquids lighter than water: sp. gr. = 140/(°Bé + 130) liquids heavier than water: sp. gr. = 145/(145 - °Bé)
Note that a "new" scale called the Gerlach scale uses 146.78 in the heavier-than-water equation rather than 145.

Although the Baumé scale is almost never mentioned in chemistry courses, tradesmen often use it as a convenient way to check solution concentration. For example, U. S. Grade A honey must have a Baumé reading of at least 42.49°Bé at 60°F. Recipes for lowering the pH of pool water call for 20°Bé hydrochloric acid. It's also used by brewers for checking the density of sugar solutions before fermentation.

References

CRC Handbook of Chemistry and Physics (CRC Press)
 This quintessential handbook contains data for about 2500 inorganic compounds and 12000 organic compounds. Relevant physical properties listed include crystal structure, color, solubility, melting points, boiling points, heats of formation, heats of vaporization, heats of fusion, entropies, heat capacities, critical pressure and temperature, vapor pressure, and optical properties. (Book/CDROM; no Web access). http://www.crcpress.com/catalog/9720.htm (12/12/98)

Author: Fred Senese senese@antoine.frostburg.edu

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