A widely used experiment for the physical chemistry lab in which students determine the intrinsic viscosity of poly(vinyl alcohol), or PVOH, in water has been rewritten within the POGIL Physical Chemistry Lab (PCL) framework. To investigate the effect of polymer concentration on solution viscosity, student groups begin the lab by measuring flow times, in an Ubbelohde dilution viscometer, of solutions of selected concentrations prepared from a single stock solution of PVOH in water. These flow times are then subsequently used to calculate relative and specific viscosities, with student groups discovering these concepts by answering critical thinking questions to examine the data. From plots involving the relative and specific viscosities, the intrinsic viscosity for the polymer sample is determined. In the second phase of the laboratory student groups repeat the previous experiment, this time carefully planning which solution concentrations to utilize in their measurements, with each group using a solution containing a polymer of a different molar mass. From class intrinsic viscosity data, an additional log-log plot of intrinsic viscosity versus molar mass yields the Mark-Houwink parameters "a" and "K". Student groups make comparisons between these two values and those found in the literature, in addition to determining the shape of PVOH in water based on the "a" parameter. Ultimately, through this laboratory exercise students are introduced to polymer viscosity measurements, as well as graphical methods used to uncover information about polymer solution properties, all within a guided inquiry framework.

Guided inquiry experiment involving the intrinsic viscosity of a polymer in aqueous solution

256th National Meeting (2018)

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