On the Web
JCE Data-Driven Exercises
Determination of Partial Molar Volumes in Aqueous Solutions of Ionic Compounds by Arthur Ferguson, Department of Chemistry, Worcester State College, Worcester, MA 01602;
[email protected] Keywords: Upper-Division Undergraduate, Physical Chemistry, Computer-Based Learning, Inquiry-Based/Discovery Learning, Thermodynamics, Solutions/Solvents, Aqueous Solution Chemistry
Students often think that the partial molar volume (PMV) of a component in a solution is the volume of one mole of that component in the solution rather than the rate at which
764
edited by
W. Tandy Grubbs Stetson University DeLand, FL 32720
the volume of the solution changes as the number of moles of that component is changed, all other conditions being held constant. In this project students are given precise density data for aqueous solutions of three ionic compounds and guided to construct graphs of solution volume versus amount (moles) of solute at constant temperature, pressure, and amount of water. They are then asked to fit the data to an equation, use it to find an equation for the PMV of the solute, and evaluate that PMV at two concentrations. In two of the three solutions the volume decreases as solute is added, over at least part of the concentration range; thus, students discover some of the PMV values they calculate are negative, which would be impossible if the PMV were the volume of the solute ions. This project also provides a starting point for a discussion of why the volume of a solution might decrease as solute is added.
Journal of Chemical Education • Vol. 86 No. 6 June 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
