Exp 4 CHM170L

September 28, 2017 | Author: Chelsea Martinez | Category: Viscosity, Properties Of Water, Solution, Liquids, Molecules
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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

Measurement of Viscosity of Liquids by Capillary-Flow Method Marquez, Ariziel Ruth.1, (Nagayo, Juan Augustus A., Maquiling, Kenth Roger A., Martinez, Chelsea M., Ocado, Patricia Andrea C.) 2 Professor, School of Chemical Engineering and Chemistry, Mapua Institute of Technology; 2Students, CHM170L/B41, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology 1

ABSTRACT The viscosity of a liquid or fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For the liquids, it corresponds to the informal concept of thickness. The objective of this experiment is to determine the viscosity of a number of normal saturated alcohols. Using capillary-flow method, the liquid sample was placed inside the viscometer. As these samples flow, the duration that the liquid travelled from the upper meniscus to the lower meniscus marks of the said apparatus was taken notice using a timer. By varying the conditions, such as the concentration, the temperature and the sample itself, a change can be observed which can be related to the intermolecular force, size, and shape of the molecules present at the sample. The computations were carried out using the Hagen-Poiseuille equation. Through observation, it can be said that the samples containing longer chains of molecules, stronger intermolecular forces of attraction and greater molecular weight, tend exhibit higher viscosity. When it comes to changing the concentration ratio of the solute versus the solvent, it can be deduced that increasing the concentration of the solute results to a more viscous solution. Finally, upon changing the temperature on a test substance, it was observed that increasing the liquid’s temperature reduces its viscosity. This phenomenon is caused by the activity of the molecules in the sample. Increasing the temperature heightens the movement of the molecules and lessens the hold of the intermolecular forces, thus making the sample less viscous. Keywords: Viscosity, capillary-flow method, Hagen-Poiseuille equation

INTRODUCTION MATERIALS

AND METHODS

Experiment 01│ Group No. 7│ June 8, 2016

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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

Experiment 01│ Group No. 7│ June 8, 2016

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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

RESULTS and DISCUSSIONS An Ostwald-Fenske viscometer is what this experiment essentially exploited where the time required for the upper meniscus of the liquid in the feed bulb to pass two calibration marks was determined in able to get the viscosity of the given samples. Viscosity is referred to as the liquid’s resistance to flow which means that the higher viscosity the higher the liquid’s resistance to flow and vice versa. There are different factors that affect the viscosity of liquids like: temperature and concentration In dealing with viscosity, intermolecular forces play a major role. Greater attractions between molecules in a certain liquid allow them to be more intact, closer to one another, and make them become denser, thus having the greater resistance to flow. Table 1. Viscosity of Pure Liquids

Sample

Flow time through Ostwald viscometer, s

Calculated viscosity, kg/ms

Literature value of viscosity, kg/ms

% Error

Water

117

7.90 x 10-4

7.90 x 10-4

0

Ethanol

210

1.13 x 10-3

1.10 x 10-3

2.73

Ethylene Glycol

1692

1.30 x 10-2

1.70 x 10-2

23.5

1Butanol

446

The viscosity of different pure liquids and solutions were observed. Ethanol exhibited a higher viscosity than water. It has something to do with their relative shapes. The carbon chain of the molecules of ethanol tends to become entangled rather than slip past to another as the water molecules do. Same goes for 1-butanol. It exhibited a higher viscosity than both water and ethanol. Its long carbon chain is what accounts for its high viscosity. Its molecules tend to slip past another. As for Ethylene glycol that has a longest carbon chain among the samples, hydrogen bonding in this case can occur at three sites. It enables the bonding among the molecules, thereby increasing the attraction eventually leading to greater resistance to flow. The molecular basis the viscosity explains how viscosity works for a liquid on molecular level. Fundamentally, the more viscous liquids are those possessing greater molecular weight. Greater molecular weight also corresponds for a larger molecule. The larger molecule tend to slow down when flowing especially on a pipe with very small diameter, like the Otswald viscometer used in this experiment. The results of the experiment confirms this basis. Referring again to Table 1, ethylene glycol having the highest molecular weight of all the four samples also exhibited the highest value for viscosity, followed by 1butanol then ethanol and lastly water which has the smallest molecular weight and viscosity. Table 2. Effect of salt concentration on viscosities of aqueous solutions NaCl Concentration 0

2.40 x 10-3

2.08

Calculated viscosity, kg/ms

117 7.90 x 10-4

0.2

146 9.87 x 10-4

0.5 2.45 x 10-3

Flow time through Ostwald viscometer, s

139 9.40 x 10-4

1

132 8.93 x 10-4

Room Temperature, H2O: 33.5˚C Room Temperature: 28˚C

Experiment 01│ Group No. 7│ June 8, 2016

The second part of the experiment dealt with the effect of salt concentration on the viscosity of aqueous solutions. Specifically the salt involved is sodium chloride, having varying concentrations of 0.2 M, 0.5 M and 1.0 M. Referring

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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

to the results gathered, it can be inferred that the viscosity increases as the concentration of the solute increases. It can be observed (see Table 3) that the concentration and the viscosity of the solution have a direct proportionality. Increasing the salt solution concentration caused an increase to the viscosity. While NaCl dissolves in the solution, its ions dissociate in the solution as well. H+ and OH- of the water also partake in the dissolution. What dominates is the ionic attraction between the salt molecule and water molecules. Hence, increasing the NaCl concentration also increases the ionic attraction between molecules. High concentration of the solute leads to a solution of more viscosity. The solutions are more viscous than pure water. This is because the dissolved solutes gets between the dissociated water molecules, increasing the forces of attraction between them which results to greater resistance in flowing. For concentrations of 0.5 M and 1.0 M, the data were not consistent. Possible source of error was human error while using the timer.

Table 3. Temperature effects on viscosity of water Temperature, o C

Flow time through Ostwald viscometer, s

Calculated Viscosity, kg/ms

33.5

117

7.90 x10-4

38.5

110

7.43 x10-4

43.5

102

6.89x10-4

48.5

95

6.42 x10-4

Another factor affecting the viscosity of a liquid is the temperature. The third part of the experiment sought to determine the temperature effect to the viscosity of water (see Table 3). Beginning with the room temperature and then eventually increasing it at an increment of 5oC, the effect of the temperature to the viscosity of the water was concluded. Viscosity can also be affected by the temperature at which the molecules are in. It was observed that increasing the temperature of the water decreases its time of flow through the Otswald viscometer. Increasing the temperatures means increasing the average kinetic energy of the molecules. This is by the direct proportionality between them. By this means, the ability of the water to flow also increases. As the temperature is increased, the kinetic energy of the molecules in a substance increases. The shearing effect decreases as well as the intermolecular force, which results to a lower viscosity

Experiment 01│ Group No. 7│ June 8, 2016

Temperature and viscosity are inversely proportional to each other as shown in the results of this experiment. The higher the temperature, the lower the viscosity, the more the liquid will be able to flow. This is due the higher energy that hotter liquids possess; this makes the liquid be able to flow more easily when its temperature is high. On the hand, the concentration of solutions and their viscosity are directly proportional to each other as shown in the results of this experiment. The higher the concentration the, the higher the viscosity, the more the liquid will be able to resist flowing. This is due to the number of solute present that can act as a roadblock that will prevent the liquid from flowing. Viscosity mainly has two kinds: dynamic and kinematic. Dynamic viscosity is expressed as the resistance of a liquid to motion, specifically flowing. The dynamic viscosity is what was observed all throughout this experiment. The kinematic viscosity is just simply the ratio of the dynamic viscosity and the density of the liquid. Kinematic viscosity is useful in analyzing the Reynold’s number. CONCLUSIONS AND RECOMMENDATIONS Subsequently performing the three parts of this experiment with comprehensive observations and calculations, sufficient data results were gathered to conclude the overall experiment. In this experiment, the viscosity of the sample liquids where obtained and recorded through the use of Ostwald viscometer. In the first part of the experiment, wherein the samples involved were pure liquids, ethylene glycol exhibited the highest viscosity while water has the lowest viscosity. As stated, viscosity is a measure of the fluid’s resistance to flow. Hence, the longer the time for the fluid to flow corresponds to higher viscosity. Intermolecular force is one factor to consider. The more constricted attraction between the molecules, the less it will flow thus the more viscous it is. Ethylene glycol has the highest viscosity because it has two hydrogen bonding, meaning it has a strong intermolecular force than the rest, followed by the 1-butanol which has a long hydrocarbon chains. The water exhibits shortest chain among the four thus it was the fastest to flow, least viscous. On the other hand, aqueous solutions where used as samples in the second part with increasing concentrations. Based from data gathered, 1.00 M has the highest viscosity among the samples (0 M, 0.20 M and 0.50 M). It is concluded that as the concentration of sodium chloride increases the viscosity also increases. It is due to the fact that sodium chloride increases the interaction between the polymer chain and water molecules.

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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

Lastly, the effect of temperature to the viscosity of water was tested. It can be inferred that increasing the temperature decreases the viscosity of the water as seen that the time of flow decreases. It is because the kinetic energy of the molecule at high temperature increases that lead to the movement of molecules to increase too. To serve as an aid for the future researchers who will be doing the same experiment, here are some recommendations. It would be better to make sure that the viscometer is in good condition, otherwise, it may result to errors in the process of acquiring the data. The timer should be started at the same time your thumb releases the tiny hole in the viscometer. Also, in doing this experiment, keen observation is recommended as one should be alert and focused in stopping the timer as the sample reaches the marked meniscus of the viscometer. Furthermore, it can be inferred that the objectives of this experiment were efficiently met.

7. Daniels, F., et.al. (1962). Experimental physical chemistry, 6th ed. McGraw-Hill Book Company, Inc. 8. Levine, 6th Edition, Physical Chemistry, e-book version.

SAMPLE CALCULATIONS Calibration t = 117 s ρH20 = 994.538 kg/m3 µH2O at T = 7.9 x 10-4 kg/m-s

REFERENCES

A ,=

1. Wen, Christopher. UCDavis Chemwiki. Viscosity. http://chemwiki.ucdavis.edu/Physical_Chemistry/P hysical_Properties_of_Matter/Bulk_Properties/Visc osity 2. Wikipedia, the free encyclopedia. Viscosity. http://en.wikipedia.org/wiki/Viscosity 3. Viscosty of Liquid. http://www.apsu.edu/robertsonr/chem361020/viscolab.pdf 4. Monika Verma, Nayan Wasnik, T. Sai Sneha and 1Sivacoumar Rajalingam. Measurement of Viscosity for Various Liquids by Using Ostwald Viscometer and Interfacing with Labview. http://www.ripublication.com/ijaer_spl/ijaerv8n19_4 4.pdf. 5. Green, D., and Perry, R. (20080. Perry’s Chemical Engineers Handbook 8th Edition. McGraw-Hill Companies. Pp 6-4 – 6-5. 6. Baluyut, J. Y. G., Caparanga, A. R., and Soriano, A. N., (2006) Physical Chemistry Laboratory Manual, Part 1, p 30

Experiment 01│ Group No. 7│ June 8, 2016

µ 7.9 x 10−4 kg /m . s = ρT kg 994.538 3 (117 s) m

(

)

A1 = 6.79x 10-9 m2

A. Viscosity of pure liquids Sample: water Calculated Viscosity µ= Aρt Ρwater =

994.538 kg/m3

t = 117 s A= 6.79x 10-9 m2

µ=( 6.79 x 10−9)(994.538

kg )(11 7 s) m3

µ= 7.9 x 10-4 kg/m-s

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CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2015-2016

B. Effect of salt concentration on viscosities of aqueous solutions NaCl concentration = 0.20M t =146 s µ = Aρt

µ=(6.79 x 10−9)(995.797

t =110 s ρH2O at 33.50C =

994.538

kg 3 m

µ = Aρt

kg )(146 s ) m3

µ=( 6.79 x 10−9)(994.538

kg )(110 s ) m3

C. µNaCl 0.20M = 9.87 x10-4 kg/m-s

Temperature effects on viscosity of water At room temperature 33.50C

µ = 7.43 x10-4 kg/m-

Experiment 01│ Group No. 7│ June 8, 2016

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