PARTIAL MOLAL VOLUME

(Last Revision: October 7, 2003)

  • ABSTRACT:

The densities of water and several concentrations of sodium solutions are determined by means of a pycnometer. Using this information the partial molal volumes of both water and salt are determined as a function of concentration.

  • TEXT REFERENCE:

"Experiments in Physical Chemistry", Nibler, Garland, and Shoemaker, Seventh Ed., McGraw-Hill, 2003, pp.172-8.

  • OTHER REFERENCES:

S. F. Sun and P. M. Serpentino, "The Determination of Partial Specific Volume," J. Chem. Ed., 51, 552-3(1974).

  • GENERAL DESCRIPTION AND THEORY:

By measuring the density of a series of aqueous solutions of salt, it is possible to calculate an apparent molal volume of the solute. This quantity may then be plotted versus the square root of the concentration. The slope of this line may then be used to calculate the partial molal volume of both the solute and the solvent. Because of the nature of the experiment, all measurements have to be very precise or the results will be poor.

  • EQUIPMENT:

Pycnometers, constant temperature water bath, balance.

  • PROGRAMS:

  • CHEMICALS:

NaCl, water.

  • DIAGRAMS:

Figure 1.

  • LABORATORY PROCEDURE:

The laboratory procedure is the same as that described in the text: a Weld type of pycnometer is used.

  • CALCULATIONS:

The calculations are performed as described in the text.

  • LITERATURE VALUES: