Handout1-ConcUnit

# Handout1-ConcUnit - CEM 834 CONCENTRATION UNITS FALL 2005...

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CEM 834 CONCENTRATION UNITS FALL 2005 This handout discusses common units of concentration and the interrelationships between these units. The convention will be followed that the solute is given the subscript 2, while the solvent is ascribed the subscript 1. A convenient table of interconversions is given at the end of this handout. A. Relationship Between Mole Fraction and Molality The mole fraction of the solute ( 29 2 X is the number of moles of solute ( 29 n 2 divided by the total moles of solute and solvent. X n n n 2 1 2 = + 2 (1) The molality (m) expresses the number of moles of solute per 1000 g solvent. Therefore, in 1000 g solvent there are m moles of solute and 1000/M 1 moles of solvent, where M 1 is the solvent molecular weight. Thus, we can write 1 1 1 2 M m + 1000 M m m M 1000 m X = + = (2) In dilute solution, this exact equation can be approximated by X m M 1000 2 1 2245 (3) To calculate the molality of a solution when the mole fraction of the solute is known, equation (2) can be rearranged to yield m X M X 2 1 2 = - 1000 1 ( ) (4) In dilute solution, this exact equation reduces to m 1000 X M 2 1 2245 (5)

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