Experiment on surface tension

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Experiment on surface tension

  1. 1. Page 1 of 13 KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF CHEMISTRY YEAR TWO (CHEM 270) PRACTICAL CHEMISTRY IV P.2.2.1 REPORT TITLE: SURFACE TENSION NAME: OPOKU ERNEST EXPERIMENT: P.2.2.1 DATE: 14TH MARCH, 2014
  2. 2. Page 2 of 13 SURFACE TENSION AIMS AND OBJECTIVES 1. To enable students familiarize themselves with how the tensiometer is used 2. To determine the surface tension of different alcohol liquids INTRODUCTION Surface tension is the property of a liquid in contact with air or vapour that makes it behaves as if it were covered with a thin membrane under tension. For example if you were to fill a glass of water and carefully place a thin razor blade onto the top of the water, it would float for a short time due to this pseudo- membrane that support it. This ``tension`` at the surface results from intermolecular forces within the solution that cause the exposed surface to contract to the smallest possible area. This is because a molecule in the interior of the solution interacts with other molecules equally from all sides, where as a molecule at the surface of the liquid is only affected by the molecules below it. This property of surface tension is responsible for formation of liquid droplets, soap bubbles, and menisci (the curved upward or downward appearance of a column of liquid).
  3. 3. Page 3 of 13 Surface tension is defined as the force acting over the surface of a solution per unit length of the surface perpendicular to the force. It is usually measured in dynes per centimeter. The SI unit is Newton per meter. Let consider these two setups a and b. (a) A molecule within the bulk liquid is surrounded on all sides by other molecules which attract it equally in all directions leading to zero net force. (b) A molecule in the surface experiences a net attractive force point towards the liquid interior, because there no molecules of the liquid above the surface. In this experiment this phenomenon would be employed to determine the surface tension of the various alcohol prepared. The measurement would be done with Du Nouy Ring Tensiometer.
  4. 4. Page 4 of 13 This type of tensiometer uses a platinum ring which is submersed in a liquid. As the ring is pulled out of the liquid, the tension required is precisely measured in order to determine the surface tension of the liquid. This method requires that the platinum ring be nearly perfect; even a small blemish or scratch can greatly alter the accuracy of the results. A correction for buoyancy must be made. This method is considered inaccurate compared to the plate method but is still widely used for interfacial tension measurement between two liquids. Du Nouy tensiometer in liquid uses a platinum ring which is submersed in a liquid. As the ring is pulled out of the liquid, the tension required is precisely measured in order to determine the surface tension of the liquid. This method requires that the platinum ring be nearly perfect; even a small blemish or scratch can greatly alter the accuracy of the results. A correction for buoyancy must be made. This method is considered inaccurate compared to the plate method but is still widely used for interfacial tension measurement between two liquids.
  5. 5. Page 5 of 13 Du Noüy Ring Tensiometer Du Noüy-Padday method, This method uses a rod which is lowered into a test liquid. The rod is then pulled out of the liquid and the force required to pull the rod is precisely measured. This is a rather novel method which is accurate and repeatable. The Du Noüy-Padday Rod Pull Tensiometer will take measurements quickly and unlike the ring and plate methods, will work with liquids with a wide range of viscosities.
  6. 6. Page 6 of 13 Application of Surface and interfacial tension measurements are extremely important in the control and improvement of: absorption cataphoresis condensation emulsification evaporation miscibility osmotic pressure solubility. CHEMICALS AND APPARATUS 1. Methyl alcohol 2. Ethyl alcohol 3. N- propyl alcohol
  7. 7. Page 7 of 13 4. N-butyl alcohol 5. Amyl alcohol 6. Du Nouy ring tensiometer 7. 100ml volumetric flasks 8. Pipette ( with disposable tips) 9. Beakers 10. Funnels 11.Distilled water PROCEDURE 1. Pipette (each alcohol was assigned to one disposable tip) a specified volume of the alcohol as stated below. Alcohol Volume measured/ml Methyl alcohol 0.40 Ethyl alcohol 0.58 n-propyl alcohol 0.75 n-butyl alcohol 0.92 Amyl alcohol 1.08
  8. 8. Page 8 of 13 2. The measured volume was then diluted to 100ml to make up a concentration of 0.1M and the surface tension determined using Du Nouy tensiometer. 3. The surface tensions of the following Molar (M) of amyl alcohol were determined using the Du Nouy tensiometer 0.01, 0.02, 0.04, 0.06 and 0.10. TABLE OF RESULTS Alcohol Surface tension in mJm-2 Methyl alcohol (MeOH) 68.0 Ethyl alcohol (EtOH) 63.0 n-Propyl alcohol (n-PrOH) 62.0 n-Butyl alcohol (n-BuOH) 59.0 Amyl alcohol (AmOH) 54.0 Amyl alcohol in Molar Volume measured Surface tension 0.01 0.108 20.0 0.02 0.216 55.0 0.04 0.432 52.0 0.06 0.648 48.0 0.10 1.080 54.0
  9. 9. Page 9 of 13 0 10 20 30 40 50 60 70 80 0 1 2 3 4 5 6 SURFACETENSION NUMBER OF CARBON ATOM IN ALCOHOL Surface tension 0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 SURFACETENSION CONCENTRATION OF AMYL ALCOHOL Surface tension
  10. 10. Page 10 of 13 Slopes of the alcohol (number of carbon) Number of carbon Slope 1 6.67 2 13.33 3 3.33 4 5.00 5 8.57 Slopes of amyl alcohol Concentration of amyl alcohols Slope 0.010 2500 0.020 218.75 0.040 -333.33 0.060 333.33 0.100 500 T(C) = C X slope for number of carbon RT T(C1) = 0.1 x 6.67 = 2.692 x 10-4 2477.71 = 0.1 x 13.33 = 5.38 x 10-4 2477.71 = 0.1 x 3.33 = 1.344 x 10-4 2477.71 = 0.1 x 5.00 = 2.018 x 10-4 2477.71 = 0.1 x 8.75 = 3.531 x 10-4 2477.71 T(C) = C X slope for concentration RT = 0.010 x 2500 = 1.009 x 10-2 2477.71 = 0.020 x 218.75 = 1.77 x 10-3 2477.71 = 0.040 x -333.33 = -5.38 x 10-3 2477.71
  11. 11. Page 11 of 13 = 0. 060 x 333.33 = 8.072 x 10-3 2477.71 = 0.100 x 500= 2.018 x 10-2 2477.71 DISCUSSION It could be observed from the graph that surface tension against number of carbons of the alcohol decreases as the number increases. This could accounted for the reason being that as the number of carbon increases the entropy level of the solution increases therefore limiting its elastic ability. For the other graph of surface tension against concentration of amyl alcohol, the surface tension decreases as the concentration of the amyl alcohol increases. The number of molecules interacting in the solution increases therefore disturbing the surface tension. PRECAUTIONS 1. The ring of the tensiometer should not be touched with the fingers. 2. The tensiometer was standardized with cold water.
  12. 12. Page 12 of 13 3. The experiment was assumed to have been done under an ideal condition, which is the room temperature was assumed to be 25o C. CONCLUSION The goals of the experiment were achieved. It is known that as the number of carbons increases, surface tension also decreases. For the amyl alcohol, as it concentration increases it surface tension also decreases. REFERENCES 1. `Experimental physical chemistry` Daniels, William and others pg 321-328 2. Chemical Technician Ready Reference Handbook 2nd edition by Shugar and Bauman pages 592- 593 3. Textbook of Practical Chemistry 4th edition (2001) by Wesley. D. Smith pages 620-633. 4. Parker MD, York P, Rowe RC. Bindersubstrate interactions in wet granulation. 2: The effect of binder molecular weight. Int J Pharm, 1991; 12: 243-249. 5. Riley CK, Adebayo SA, Wheatley A, Asemota HN. Surface properties of yam (Dioscorea sp.) starch powders and potential for use as binders and disintegrants in drug formulations. Powder Technol, 2008; 185: 280-285. 6. Fell JT, Mohammad HAH. The wetting of powders by bile salt solutions and gastric juice. Int J Pharm, 1995; 125: 327-330. 8. Hörter D, Dressman JB. Influence of
  13. 13. Page 13 of 13 physicochemical properties on dissolution of drugs in the gastrointestinal tract. Adv Drug Deliv Rev, 2001; 46: 75-87.

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