Name: Seduco, Rhett Adrian C. Ubas, Johnziel G.
Date Performed: Group No.
09/28/2017 11
Experiment No. 4 The Radius of a Molecule from Viscosity Measurements I.
Background
Viscosity is the measure of internal friction between molecules in a flowing fluid. The higher the value of viscosity the slower is the flow of the fluid under otherwise identical conditions (Malijevsk´y, et al., 2005). Viscosity persists because only a part of that fluid moves, causing it to force other neighboring parts to move along with it causing an internal friction between the molecules which ultimately leads to a reduced rate of flow (chem.libretexts.org, 2017). According to kinetic theory, viscosity in gases at low and medium pressures increases with temperature and does not depend on pressure. The description of the viscosity of real gases by kinetic theory is relatively correct. The viscosity of liquids is higher than that of gases. It increases (slightly) with pressure 1 and decreases with increasing temperature (Malijevsk´y, et al., 2005). Viscosity of a solution is dependent on many factors such as temperature, viscosity of the solvent type of the solute, and the amount of solute. Few assumptions must be made to be able to formulate a simple equation that relates the viscosity of the solution with the parameters that affect the viscosity. The first is assuming the shape of the solute particles in the solution as spheres. The second is assuming the solvent is continuous, where the solvent is represented as a continuous medium instead of individual explicit solvent molecules. The last assumption could be true of the particle size of the solute is much bigger than that of the solvent. The relation of these assumptions is explained b y the equation shown below:
= 1 + 2.5 This equation can also be expressed in the form:
= 1 + 6.310213 At the other side of the experiment, atomic radius is defined to be the total distance from an atom’s nucleus to the outermost orbital of electron. In simpler terms, it ca n be defined as something similar to the radius of a circle, where the center of the circle is the nucleus and the outer edge of the circle is the outermost orbital of electron. Atomic radii is useful for determining many aspects of chemistry such as various physical and chemical properties (chem.libretexts.org, 2017). This experiment objectively aims to determine the radius of the glycerol molecule, prepare a solution of one gram of glycerol in every liter of solution, record the time it took
for the stated solution with a given volume to completely flow through a viscometer, also record the time of flow for the identical volume of water through a viscometer, and finally, show the graph of relative viscosity plotted against the concentration.
II.
Results
Table 4.1. Data gathered from the experiment and solution for ƞ/ ƞ concentration (g/L) 0 0.25 0.5 0.75 1
concentration (mol/L) 0 0.002714623 0.005429246 0.008143869 0.010858492
t (in s)
10.31 10.71 10.85 10.98 11.03
t/t
1 1.038797 1.052376 1.064985 1.069835
₀ d/d
1 1.000057 1.000114 1.000171 1.000228
Table 4.2. Percent Error of the Radius of Glycerol (C3H8O3) Molecule Parameter R experimental theoretical % error
Value
9.91047E-09 3.10E-10 3096.93%
ƞ/ƞ
1 1.038857 1.052496 1.065168 1.070079
Figure 4.1. concentration (mol/L) vs ƞr
III.
Discussion and Recommendations
As previously discussed in the background section, viscosity is the measure of internal friction between molecules in a flowing fluid. The higher the value of viscosity the slower is the flow of the fluid under otherwise identical conditions (Malijevsk´y, et al., 2005). In this case, the experimenters looked at glycerol, a trihydroxylalcohol (chem.libretext.org, 2017), with the purpose of determining its atomic radius. Regarding the relationship between the viscosity and how vast its radius would be, liquids with smaller molecules will have a lower viscosity than one with larger molecules because smaller molecules can easily slide past one another. Larger molecules tend to cause congestion. Furthermore, larger molecules also have stronger intermolecular forces – such as London Forces – which attract them to one another with greater strength and hinder molecular flow, resulting in higher viscosity (Cascio, 2017). Referring to the attached Excel file, those trials with higher concentrations of glycerol solution resulted to longer time for them to flow completely through the viscometer. The time recorded were 10.31, 10.71, 10.85, 10.98 and 11.03 seconds, again with respect to increasing concentrations pure water, 25%, 50%, 75% and 100% glycerol. This is due to how much glycerol atoms there are in the solution. This presence caused the solution to become more viscous taking up more time as they become more concentrated. Thus hypothetically saying, glycerol atoms have larger atomic radius than water.
This experiment was done by making a solution out of water and glycerol, diluted up to a certain volume. This was preceded by preparing five sets of this mixture of increasing concentration: pure water, 25% glycerol in water, 50% glycerol in water, 75% glycerol in water and 100% glycerol solution. Observations were obtained with the use of a Viscometer. The respective time for each concentration to flow through was also recorded and taken note of. These results were then plotted into a graph. Using the given equations and formulas, the desired values were calculated and the radius of glycerol was determined, settling at 3.10E-10 in comparison to the value obtained through observation: 9.91047E-09 bearing the percent error of 3096.93%. The experimenters recommend that the experiment would yield better and more accurate results if the procedure were thoroughly followed as such minor changes may/can result in errors. Also, multiple trials would consider more correct sets of data. Dilution processes must always be correct also – this can lead to procedural and human errors if egregiously practiced.
IV.
Calculation
A. Radius of glycerol (C3H8O3) molecule
= √ 6.310 4 ₀
B. d/d
and
₀
ƞ/ ƞ
= 1+0.021 ƞ ƞ₀ =
C. Other Significant Calculations (refer to attached Microsoft Excel file)
V.
Conclusion
The relationship between viscosity and radius of the molecule is shown as directly proportional with each other. That is, as one of them increases, the other is also expected to increase.
VI.
References
Prof. Ing. Nov´ak, Josef P. CSc., Prof. Ing. Lab´ık, Stanislav CSc. and Ing. Malijevsk´a, Ivona CSc. (September 30, 2005). Physical Chemistry in Brief. Institute of Chemical Technology, Prague. n.a. (31 January 2017). Viscosity. Retrieved on 5 October 2017 from https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Physical_Properties_of_M atter/States_of_Matter/Properties_of_Liquids/Viscosity n.a. (07 Sepetember 2017). Atomic Radii. Retrieved on 5 October 2017 from https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Physical_Properties_of_M atter/Atomic_and_Molecular_Properties/Atomic_Radii n.a. (25 April 2016). Size of a Molecule from Viscosity Measurements. Retrieved on 05 October 2017 from https://www1.udel.edu/pchem/C446/Experiments/exp8.pdf Cascio, Christopher. (24 April 2017). Does Viscosity Increase With the Size of the Molecule?. https://sciencing.com/viscosity-increase-size-molecule-13388.html
