液体表面张力的测定Determinationofsurfacetensionofliquids

1、液体表面张力的测定（determination of surface tension of liquids）experiment fiveexperiment five experiment fiveexperiment fivedetermination of surface tension of liquidsdetermination of surface tension of liquids - determination of surface tension of liquidsdetermination of surface tension of liquidstwo billio

2、n eight million two hundred and one thousand two hundred and five2008201205, 20082012052008201205 liu seniorliu zizheng liu zizhengliuzizheng1 objective (1) to determine the surface tension of ethanol solution with different concentration, and calculate the surface adsorption capacity and the transv

3、erse of ethanol moleculesectional area.(2) to understand the properties of surface tension and the relationship between surface tension and adsorption capacity.(3) grasp the principle of maximum bubble pressure method for measuring surface tension and surface adsorption capacity of solution. 2 the p

4、rinciple of experiment is that in a liquid interior, the attraction of any molecule is balanced. but on the surface of the liquidthe molecules are different. because the molecules on the surface layer are attracted by the molecules in the liquid layer on the one hand, they are exposed to the otherth

5、e attraction of gas molecules outside the liquid, and the action of the former is greater than that of the latter. therefore, on the surface layer of liquid surfaceeach molecule is subjected to an unbalanced force that is perpendicular to and directed toward the interior of the liquid. this appeal i

6、s apparent on the surfacethe molecules push inward to make up the smallest area of the liquid. to increase the surface area of a liquid, it is necessary to have resistanceto do work, increase the potential energy of molecules. therefore, molecules are larger in the surface layer than in the liquidpo

7、tential energy, which is surface free energy, usually increases the maximum work required by the surface of a square meter by a or increasesg change of surface free energy by a square meters, known as the surface unit surface energy, and its unit is j - m-1;the force acting on the surface of a liqui

8、d and the unit in its length that is used to shrink it is called surface tensionforce, whose unit is n. m-1. the surface energy of a unit surface of a liquid is equal to its surface tension.if the surface area of the liquid is increased by s, the reversible work a shall be:-a = g = gamma s (1)the su

9、rface tension of liquid is related to temperature. the higher the temperature is, the smaller the surface tension is. at the critical temperature,liquids and gases are divided, and surface tension approaches zero. the surface tension of a liquid is also related to the purity of the liquidin a pure l

10、iquid (solvent), if the impurity (solute) is added, the surface tension changessmall depends on the nature of the solute and the amount added.for pure solvents, the surface layer is the same as the internal, but not the solution. whenwhen the solute is added, the surface tension of the solvent chang

11、es. according to the principle of minimum energy, if the solute can dissolvethe surface tension of the agent is that the solute concentration in the surface layer should be greater than the concentration in the solution, if the added solute canif the surface tension of the solvent is raised, then th

12、e concentration of the solute in the surface layer should be lower than the concentration inside the solution. thisthe phenomenon that the surface concentration is different from the concentration of the solution is called surface adsorption of the solution. at a certain temperature and pressureforc

13、e,the surface tension of solution and the amount of adsorbed solute solution and adding the solution quality (i.e. concentration)the relationship between them by gibbs (gibbs) said:type: for the adsorption of mol.m (gammathe concentration of r (mol.l-1);is the gas constantthe change of surface tensi

14、on temperature change with solution concentration rate (gamma? /? c) t <0, >0, gamma surface layer, the concentration is greater than the concentration of the internal solutioneffect。 if gamma with increasing concentration of thethe degree of concentration is less than the solution itself,the

15、adsorption of solutes and concentration of cc/ gamma map, a straight line,if the molecular n represents 1m2 surface solute numberwhere l is avogadro constantfrom (2) can be seen, as long as the concentration and determination of surface tension of solutionthe adsorption amount of gamma solution.in t

16、his experiment, the measurement of the concentration of solution is the correspondence between the application concentration and refractive indexis an application of the maximum bubble pressuretutuchartone1.1.1.beakerbeaker;2.;2.2.figure 2. 2-1is a schematic diagram of apparatus for measuring surfac

17、e tension of the maximum bubble pressure methodinstalled in the branch tube 5, the capillarygamma = - (t)(mol.m-1); gamma surface tension (j, m-1); tabsolute temperatureis the gas constant (8.314j.k-1 - mol-1). (gamma? /? c change of surface tension temperature change with solution concentration rat

18、e. if gamma decreases with the increase of the concentration ofthe concentration of surface layer is greater than the concentration of the internal solutionwith the increasing concentration (i.e.gamma? /? c) t >0, <0, gamma surface layer, the solution concentrationthat is called negative adsor

19、ption.the relationship between c with langumuir isothermal adsorption equationcgammathecgamma -onegamma - kthus, the slope of the line and the intercept can be obtained by constant k and gammathe number of solute molecules on the surface, then:n= gamma - lthis can be a constant, each molecule in the

20、 cross-sectional area occupied by the surfacegamma - am=1/as long as the determination of the solution concentration and the surface tension can be obtained under different concentrationsthe measurement of the concentration of solution is the correspondence between the application concentration and

21、refractive index,is the maximum bubble pressure method.charttutufigure 2twenty-two2-1elevenonemaximumthe biggestmaximumdetermination of surface tension of bubble method apparatusdetermination of surface tension device of bubble method determination of surface tension of bubble method equipmentdeterm

22、ination of surface tension of bubble method apparatustwo2.2.2. drop funnelthe dropping funnel drop funneldrop funnel;3.;3.3.differential pressure measuring instrument 3. digital microdigital micro differential pressure measuring instrument digital micro differential pressure measuring instrumentdiff

23、erential pressure measuring instrument digital micro;4.;4.4.4. thermostatthermostat thermostatthermostatic device;five5.5.5. with a branch tubewith a branch tube with branch tubetest tube with branch pipe;6.;6.6.6. capillarycapillary capillarycapillaryis the maximum bubble pressure method of measuri

24、ng surface tension device diagram. a liquid that will test surface tensionthe end surface of the capillary 6 is tangent to the liquid surface and the liquid surface rises along the capillary tube(2)for absolute temperature (k) and c for c), t meansdecrease with the increase of concentrationat this p

25、oint, the concentration of the solution surface layer is greater than the concentration inside the solution, which is called positive adsorptionthe concentration of the solution surface layer at this timeisothermal adsorption equation representation:gamma infinity.thus, the sectional area occupied b

26、y each molecule on the surface is am:it can be obtained at various concentrationsmeasurement of surface tensiona liquid that will test surface tensionthe liquid surface rises along the capillary and opens the drop funnel. 2 of the piston slowly draws air, because the pressure on the liquid level in

27、the capillary (p atmosphere) at this timeit is larger than the pressure on the surface of the tube in the test tube (p system), so the liquid level in the capillary gradually drops, and the bubble slowly escapes from the capillary tube end. during the formation of bubbles, the concave surface is pro

28、duced because of the surface tensionan additional pressure p is pointed out to the outside of the liquid level, so there is the following relationship:p atmosphere = p system + delta pp = p, the atmospheric p system (3) additional pressure p is proportional to the surface tension of the solution, an

29、d is inversely proportional to the radius of curvature of the bubble rtie typep = 2, gamma /r (4)if the diameter of the capillary is small, the bubbles formed can be considered spherical. when bubbles are formed just because of the surfacealmost flat, so the radius of curvature is very large. when t

30、he bubble is hemispherical, the radius of curvature is equal to capillarythe tube diameter is r, and the r value is minimum at this time. as the bubble increases further, it increases only (see figure 2),until the liquid level escapes. according to (4), when r = r, the additional pressure is the max

31、imump = 2, gamma /r (5)this maximum additional pressure can be read on the digital micro pressure differential meter.charttutufigure 2twenty-two2-2twenty-twofig. 2 schematic of bubble formationschematic diagram of bubble formationschematic diagram of bubble formationin the experiment, the r is a con

32、stant if the same capillary and manometer are used. if knownsurface tension of liquid as a standard, after the experiment measured its delta p, you can find r. then just use this onethe p value of other liquids can be measured by the instrument. the surface tension of various liquids can be obtained

33、 by calculating the (5) formula. 3 instruments and reagents(1eleven1) instrumentinstrumentinstrumentconstant temperature tank device; dp-a precise digital pressure gauge; a gas cylinder; a sample tube; a capillary tube,beaker (250ml)(2twenty-two2) drugsdrugdrugsethanol (ar) 4 experimental steps (1)

34、by the weighing method with 5%, 10%, 15% crude, 20%, 25%, 30%, 35%, 40% ethanol water solution 100mlset aside.(2) the rate of ethanol water solution index n were determined.(3) the maximum additional pressure pmax determination of water: 2003oneopen the precision digital pressure gauge at 10min. the

35、 unit to mmh2o, in the atmosphere under the condition of instrumentzero for mining.2003twothe instrument is to be adopted zero measurement system, and the thermostatic bath sample tube placed in the temperature of 25 deg in the constant temperature 10min,then open the bottle drops below the capillar

36、y pressure, the bubble control one by one to escape, about 510s drum out of a bubble.it can be observed that the differential pressure gauge shows the pressure difference increases, the pressure difference reaches a maximum when the instrument display valuehave a short stay a few seconds, read the m

37、icro manometer pressure maximum value at least three times average.(4) to (3) in steps,twothe maximum additional pressure was the pmax concentration of ethanol water solution value. 5 experimental data recording and processing at room temperature: 16.1 degreesatmospheric pressure: 102.70kpa(1eleven1

38、)the refraction rate of ethanol water solution)refraction refraction rate of ethanol aqueous solution of ethanol water solution ratethe refraction rate of ethanol water solutionin the literature 25 degrees of concentration and refractive index of ethanol water solution rate as shown in the following

39、 tabletabletable 5fifty-five5-1 25125125125 cc cc. ethanolwhen ethanol and ethanolwhen ethanol-concentration and refractive solution ratethe concentration and refractive solution concentration and refractive rate solution ratethe rate of aqueous solution concentration and refractive indexc/ (mol.l-1

40、)0.91 1.70 2.62 3.55 4.10 5.21 8.58 12 13.59 17.17n 1.332fiveone point three three fiveeightone point three three eightzeroone point three four onezeroone point three four fourzeroone point three four sixtwoone point three four ninetwoone point three five seveneightone point three six twooneone poin

41、t three six threenineone point three six ninesixwater refractive index of 1.3330 test, and measured 8 groups of ethanol aqueous solution refractive rate obtained after calibrationthe following tabletabletable 5fifty-five5-2 8282828 ethanol groupgroup ethanol ethanol groupethanol group- water solutio

42、naqueous solutioncalibration solutioncalibrationcalibration of refractive indexrefractive indexrefractive indexthe solution concentration of 5% 10% 15% 20% crude with 25% 30% 35% 40%the refractive index n, 1.33451.3365 1.3390 1.3410 1.3475 1.3495 1.3515 1.35351.3345 1.3365 1.3390 1.3410 1.3475 1.349

43、5 1.3515 1.35351.3345 1.3365 1.3390 1.3410 1.3475 1.3495 1.3515 1.3535the average refractive index of n 1.3345 1.3365 1.3390 1.3410 1.3475 1.3495 1.3515 1.3535the use of literature data for nc curve fitting data in figure 5-1, pictured right:charttutufigure 5fifty-five5-1111 ethanolethanolethanol-wa

44、ter solutionwater solutionwater solution ncncncnc standard curvethe standard curve of standard curvethe standard curve (leftleftleft) and data fittingand fitting the data and fitting dataand fitting data (rightright rightright)according to the standard curve, the solution concentration read table 5-

45、3 tabletabletable 5fifty-five5-3thirty-threethreeeighteighty-eight8 ethanol groupgroup ethanol ethanol groupethanol group-the actual concentration of aqueous solutionthe actual concentration of the actual concentration of the water solution.the actual concentration of aqueous solutionthe solution co

46、ncentration of 5% 10% 15% 20% crude with 25% 30% 35% 40%n 1.3345 1.3365 1.3390 1.3410 1.3475 1.3495 1.3515 1.3535c/ (mol.l-1) 0.47 1.63 2.56 5.58 6.51 7.44 (8.37(2twenty-two2)measuring surface tension of liquid)the surface tension measuring surface tension of the liquid to be measured liquidmeasurin

47、g surface tension of liquidsurfacetabletable 5fifty-five5-444fourthe determination of sample surface tensionthe measurement to the determination of the surface tension of the sample surface tensionthe determination of sample surface tensioncrude with ethanol watersolution concentrationc/ (mol.l-1)pm

48、ax / kpa / pmax (average)kpagamma / (n.m-1)0 (distilled water) - 0.682 0.681 0.681 0.681 0.07205% 0.540 0.539 0.540 0.540 0.057110% 0.47 0.479 0.480 0.475 0.478 0.050515% 1.63 0.463 0.467 0.465 0.465 0.049120% 2.56 0.415 0.412 0.412 0.413 0.043625% 5.58 0.335 0.334 0.335 0.335 0.035430% 6.51 0.317 0

49、.319 0.314 0.317 0.033535% 7.44 0.310 0.309 0.312 0.310 0.032840% 8.37 0.300 0.301 0.303 0.301 (0.0318(3thirty-three3)do)dogammagamma gammagamma-cccc curvecurvecurve,for each concentration, slope undercalculate the slope of each concentration under the calculated slope of each concentration.calculat

50、e the slope of each concentration:y = a + b * xparameter value error-1.33551 a 0.00106b 0.00215 1.27518e-4-r sd n p-figure 0.002311 <0.0001 0.98459tutufigure 5fifty-five5-2 25225225225 cc cc solution drawingunder the solution drawn under the solution drawnunder the solution of gamma renderinggamm

51、a gammagamma-cccc curvecurve(curve(leftleftleft) and data fittingand fitting the data and fitting dataand fitting data (rightright rightright)calculate the slope of each concentration under the table tabletabletable 5fifty-five5-5555 samplesample the samplethe sample (in the / in)t)ttt,p.pppethanol solutionc/ (mol.l-1)0.47 1.63 2.56 5.58 6.51 7.44 8.37(gamma? /? c) t,-0.00494 -0.00428 -0.00374 -0.00201 -0.00148 -0.00094 (-0.00041(4forty-four4)by using the gibbs isotherm equation)by using the gibbs isotherm equation using the gibbs adsorpt