Physical Chem lab report：Viscosity
Running Head: Viscosity
Experiment 4: Viscosity
Austin Torres
CHM364: Physical Chemistry Laboratory
Douglas Corsi, Hao Du
2 November 2018
Abstract
Viscosity of a fluid was measured by using a viscous liquid and cleaving it. The liquid was analyzed before and after the cleaving with KIO3. Overall, the viscosity decreased with respect to time as the solution was increasingly diluted. As a polymer, the method that we evaluated this was by using a value Δ. Our calculated value of Δ was found to be 1.447*10^-5, very far from the known value of 0.02. This is the ratio of head-to-head vs head-to-tail linkages in the original polymer which were cleaved in the progression of the reaction.
Introduction
Viscous liquids exist due to intermolecular forces that can resist the flow of gravity. Rather than behaving typical they are often diverging from the ideal liquid. Many molecules made of repeating units (polymers) are viscous due to their complexity in structure. They are usually linked in a head to tail manner but can exhibit a head to head imperfection. This is the main objective of the lab. In this experiment, we used KIO4 to specifically degrade the polymer at these 1,2-glycolytic linkages. We use viscosity measurements to see our head to head linkages in the polymers. We have a formula for Δ, the increase in the number of molecules after cleavage divided by the total number of monomer units present in the system. We use this to obtain:
mn is the average molar mass of polymer before cleavage and M’n is the average molar mass of the polymer after cleavage. 44 is the molar mass of polyvinyl alcohol.
Materials and Methods
Electronic Scale
Dry Polymer
Weight Boats
50 mL pipette
100 mL volumetric flask
250 mL volumetric flask
100 mL beaker
250 mL beaker
250 mL Erlenmeyer flask
Digital viscometer (DV-E viscometer, 115V/60Hz)
8-9 grams of dry polymer was added to a beaker where it was then filled with water, approx 200 mL. It was then heated to allow the polymer to gain energy. Only reacted polymer was considered for the reaction. Once cooled, the solution was then transferred to a 20 mL flask and serial dilutions were performed to obtain 1/2, 1/4, and 1/8 solutions. To degrade these solutions, 50 mL of polymer was added to a flask along with 25 mL of water and .2548 grams of KIO4 to react, there was stirring and heating involved. The solution was then diluted to ¾, ½, and ¼ dilution. 80 mL of glycerol was added to 100 mL flask and it was filled with methanol. This is also to obtain a stock solution where ½, ¼, and ⅛ dilute solutions were made. We then measured viscosity via a viscometer.
Data and Calculations
|
Pre-Cleave |
||||
|
|
Stock |
1st Dilution |
2nd Dilution |
3rd Dilution |
|
Viscosity |
20 |
10 |
8 |
7 |
|
n(sp) |
10.7590511 |
5.37952553 |
4.303620421 |
3.765667868 |
|
Concentration (g/100mL) |
2.37 |
1.7775 |
1.185 |
0.5925 |
|
1/concentration |
0.42194093 |
0.5625879 |
0.843881857 |
1.687763713 |
|
n(sp)/c |
4.53968399 |
3.02645599 |
3.63174719 |
6.355557583 |
|
1/concentration*ln(n/no) |
0.26159701 |
0.34879601 |
0.523194021 |
1.046388042 |
|
Y int for n(sp)/c vs c |
6.024 |
|
|
|
|
Y int for 1/c*ln(n/no) vs c |
1.192 |
|
|
|
|
Post-Cleave |
||||
|
|
Stock |
1st Dilution |
2nd Dilution |
3rd Dilution |
|
Viscosity |
15.55 |
15 |
12 |
11 |
|
n(sp) |
8.36516219 |
8.06928829 |
6.455430631 |
5.917478078 |
|
Concentration (g/100mL) |
1.18 |
0.885 |
0.59 |
0.295 |
|
1/concentration |
0.84745763 |
1.1299435 |
1.694915254 |
3.389830508 |
|
n(sp)/c |
7.0891205 |
9.11783987 |
10.94140785 |
20.05924772 |
|
1/concentration*ln(n/no) |
0.52541094 |
0.70054793 |
1.05082189 |
2.101643779 |
|
Y int for n(sp)/c vs c |
22.34 |
|
|
|
|
Y int for 1/c*ln(n/no) vs c |
1.187 |
|
|
|
|
Viscosity Intrinsic |
(2*10^-4)*Mv^0.76 |
|
Mv/Mn |
1.89 |
|
Mv |
403273 |
|
Mn |
762186 |
|
Mv’ |
603273 |
|
Mn’ |
609384 |
Δ=44(1/Mn - 1/Mn’) = 44(1/762186 - 1/609384) = -1.447*10^-5
Discussion
Generally, our data was consistent with the idea that viscosity such that as units degrade they will become more fluid such that they will be less viscous. Our results showed that higher concentrations of polyvinyl alcohol resulted in higher viscosity, which makes sense since the molecules are compact together. The more diluted a solution was, the less viscous it was. Once the data was plotted, it showed a rather linear relationship so it can be accepted that viscosity is inversely proportional to polymerization. We did not find a consistent value for [𝜂], our viscosity factor. Main sources of error could have resulted from the fact that the dilutions were not significant enough to detect. Also, the cleaving is random such that it will differ from situation to situation. Δ was found to be a negative value so head to head interactions would be more than head to tail. This would not make sense head to tail is the preferred structure and it would be unlikely to be as such. A redo of this lab would pay much care to the preparation of the reagents.
Conclusion
Using the viscometer, we were able to measure the thickness of a liquid such that we were able to detect the cleaving a polymer Δ was calculated and found to be -1.447*10^-5. The literature value was .02 which is off but this may due to the fact that reactivity differs from situations.
References
Dontula, P., Macosko, C. W., & Scriven, L. E. (2005). Origins of concentric cylinders viscometry. Jurnal of Rheology , 49 (4), 807.
Langer, J. (2007, February). The Mysterious Glass Transition. Physics Today , pp. 8-9.
Novikov, V. N., & Sokolov, A. P. (2004, October 21). Pissan's ratio and the fragility of glass-forming liquids. Nature , 431, pp. 961-963.