To determine the surface tension of given liquid using Stalagmometer.
1. To determine the surface tension of given liquid (ethanol) using Stalagmometer Dr. N. G. Telkapalliwar Associate Professor Department of Chemistry Dr. Ambedkar College, Nagpur 1
2. Presentation Overview 1) Aim 2) Apparatus and Chemicals 3) Theory 4) Procedure 5) Observations 6) Calculation 7) Result Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 2
3. Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. Theory Surface Tension is the one of the property of liquid. This property of liquids arises from the intermolecular forces of attraction. A molecule in the interior of a liquid is attracted equally in all directions by the molecules around it and net force is zero. But, a liquid molecule present on the surface is attracted by a net inward force called as surface tension. The liquid surface is, therefore, under tension and tends to contract to the smallest possible area in order to have the minimum number of molecules at the surface. It is for this reason that in air, drops of a liquid assume spherical shapes because for a given volume a sphere has the minimum surface area. The surface tension (γ) is defined as the force in dynes acting along the surface of a liquid at right angle to any line 1 cm in length. Surface tension is caused by the net inward pull on the surface molecules. The inward forces on the surface molecules minimize the surface area and form a drop. Units of Surface Tension CGS unit of Surface is dyne cm–1. SI unit of Surface is is N m–1. 3
4. Stalagmometer Surface tension gives a definite shape to drop of liquid. More is the surface tension, larger is the drop size. This principle is used in Stalagmometer. Stalagmometer is an apparatus with bulb and capillary. Liquid is filled in the bulb and allowed to flow through capillary in the form of drops. If the surface tension is high, larger drop is produced and number of drops are less for a given volume. Thus more is the number of drops, less is the surface tension. Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 4
5. Apparatus Required Beaker Stalagmometer Stop Watch The relative surface tension is calculated from the expression: Where, 1 and 2 are the viscosity coefficients of water and given liquid. n1 and n2 are the drops of water and given liquid d1 and d2 are the densities of water and given liquid. Knowing the value of the surface tension of water (1 ) at the temperature of the experiment, the surface tension (2 ) of the given liquid can be found. Formula Density bottle Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 5
6. Procedure Part-I : Determination of densities of water and given liquid (ethanol) 1. Clean the density bottle with chromic acid solution and then with distilled water. Rinse with water and ether and then dry. 2. Weigh an empty density bottle (W1). 3. Fill the density bottle with distilled water completely, insert the stopper and weigh again (W2). 4. Take out the distilled water and rinse the density bottle 2-3 times with given experimental liquid (ethanol). 5. Fill the given experimental liquid (ethanol) into the density bottle and record the weight again (W3). Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 6
7. Procedure Part-II : Determination of surface tension 1) Clean the stalagmometer with chromic acid solution and then with distilled water. Rinse with water and ether and then dry. 2) Attach the stalagmometer to the burette stand in exactly vertical position. 3) Hold a beaker containing distilled water and dip the lower end of stalagmometer in it. Suck the distilled water just above the mark ‘A’. 4) Allow water to flow freely. Adjust the flow rate using pinch screw clip so that it should deliver 15 to 20 drops per minutes (3-4 drops in 15 sec). 5) Count the number of drops falling between marks ‘A’ and ‘B’. 6) Repeat the recording of number of drops three times for distilled water as well as for the given experimental liquid (ethanol). Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 7
8. Observations and Calculations Part-I : Determination of densities of water and given liquid (ethanol) 1) Room temperature = …………… OC 2) Weight of empty density bottle= W1= …………. g. 3) Weight of density bottle with water= W2= …………. g. 4) Weight of density bottle with given liquid (ethanol) = W3= …………. g. 5) Volume of density bottle =V= ………. ml Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 8
9. Observations and Calculations Part-II : Determination of surface tension of given liquid (ethanol) Sr. No. Number of drops Relative Surface Tension Surface Tension For Water Mean (n1) For Ethanol Mean (n1) 1 — — — — 2 — — — — 3 — — Result: 1) Relative surface tension of given liquid (ethanol) relative to water was found to be …… 2) Surface tension of given liquid (ethanol) was found to be ………… dyne cm-1 Surface tension of water at room temperature = 1 = ……… dyne cm-1 Aim: To determine the surface tension of given liquid (ethanol) using Stalagmometer. 9
10. References • Essentials of Physical Chemistry, S. Chand Publication by Arun Bahl, B.S. Bahl, G. D. Tuli. • University Chemistry, Volume I, Alliance & Co., by R. M. Jugade. • A Text Book of Chemistry, B.sc. SEM- I, Himalaya Publishing House. The contents, materials, images, etc. used in this video/presentation are taken from open sources (Internet and Books) for educational purposes only and not meant for any commercial distribution. 10
