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Unformatted text preview: Results and Discussion: Lab 7 The effect cross-linking had on the viscosity of a polymer solution was determined. In this particular experiment, borate ions were used to cross-link strands of the polymer poly(vinyl alcohol). Note: Borate ions were obtained by dissolving borax in water, according to equation three in the Chem 207 lab manual. The ions cross-link the PVA chains by forming hydrogen bonds between strands of the polymer, as depicted in figure 7.4. To perform this experiment, a 2.030 gram sample of PVA was slowly dissolved as described in the chemistry lab manual. Once the PVA was completely dissolved, an observation was made regarding the color of the solution (clear and colorless). Heating was then discontinued, 10 drops of 0.1% methyl red indicator was added to the solution, and the beaker was allowed to cool. Meanwhile, a separate borax solution was prepared using 0.400 g Borax and 10 mL of water. Before adding the Borax solution, the initial viscosity of PVA solution was measured in three ways. First, the viscosity was compared to a common object (a “looks like” qualitative measurement). Viscosity was then measured quantitatively by: (a) timing the decent of a metal ball bearing through the solution (in seconds using a stopwatch), and...
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