SCEP 3130PHYSICAL CHEMISTRY IIIEXPERIMENT 7NAME : YONG KIM YUNG MATRIC NO.: SEP 050230PARTNERS NAME: NORIDAYU OMERMATRIC NO.: SEP 050138 LECTURER: PROF. DR. KHOO SIOW KIANDate of Experiment: 12rd March 2009Date Report submitted: 19th March 2009

INTRODUCTIONSurface activity is defined by the tendency of a particular chemical to adsorb on the surface. The concentration of chemical on the surface is higher than that of in the solution. The chemicals that have this property called surfactant. A surfactant molecule usually consists of a polarized part or an ionized moiety and an unpolarized chain namely paraffin. The polarized part for example hydroxyl group will contact with the water (aqueous phase) while the unpolarized part for example hydrocarbon group will not have any affinity towards water. Quantitatively, use the adsorption Gibbs equation to measure the surface excess concentration.

= EXPERIMENTAL1. All glasses are washed with distilled water since chromic acid is very dangerous.2. 0.1 moldm-3 alcohol solutions of methyl, ethyl, n-propyl, n-butyl and n-amyl are prepared in 100 ml volumetric flask from the alcohol solutions of 0.40, 0.58, 0.75, 0.95 and 1.08 ml, respectively.3. A torsion balance is used to determine the surface tension of each solution at room temperature.4. Solutions of amyl alcohol with concentrations of 0.01, 0.02, 0.04, 0.06, 0.08, 0.10 mol dm-3 are prepared whereas solutions of 0.15, 0.18 and 0.2 moldm-3 are readily been prepared.5. The solutions are shaking to ensure all the alcohols have been diluted and the surface tension of each solution is determined. 6. The surface tension of distilled water is determined as well.7. The step 4 and 5 above are repeated with t-butyl alcohol.8. A stock solution containing 6 g t-butyl alcohol in 100 ml solution is prepared in a 100 ml volumetric flask.9. Solutions of 0.5, 1, 3, 5, 7, 10 and 13 ml of the stock solution are diluted to 100 ml with distilled water in volumetric flasks.10. The surface tensions for the above solutions are determined.

CAUTION1. Invert or shake the solution gently to ensure complete mixing of the solution.2. Ensure that the torsion balance is at zero-point before starting the experiment to prevent error in measuring the surface tension.3. Avoid any blowing of wind as torsion balance is very sensitive to wind that can affect its measurement.

RESULTS AND CALCULATIONSTemperature = 30CThe surface tension of distilled water = (0.0725 0.0005) Nm-1

Part 1: Measure surface tension of 0.1 moldm-3 alcohol solutionsTable 1: The surface tension of 0.1 moldm-3 alcohol solutionsSampleNumber of carbon atomsSurface tension, ( 0.0005 ) Nm-1

123Average

Distilled water00.07150.07250.07000.0710

Methyl alcohol (0.10M)10.06950.07150.07050.0705

Ethyl alcohol (0.10)20.06950.06950.05750.0655

N-propyl alcohol (0.10M)30.06600.06600.06550.0658

N-butyl alcohol (0.10M)40.05650.05600.05700.0565

N-amyl alcohol (0.10M)50.05300.04250.04250.0460

Graph of versus the number of carbon atoms in alcohol is showed in Graph 1 Graph 1

Part 2: Measure surface tension of different concentration of amyl alcohol

Example of calculation of and for amyl alcohol of different concentrations:By using the equation from Graph 2: y = -0.0029x2 - 0.0275x - 0.0045Assuming x = ln C y = = -0.0029 (ln C)2 - 0.0275 (ln C) - 0.0045

= -0.0058 ln C - 0.0275

Calculation of the 0.01 mol dm-3 amyl alcohol

= -0.0058 ln C - 0.0275 = -0.0058 (-4.6052) - 0.0275 = -0.78984 x 10-3

The value of for the concentration, C can be calculated by using adsorption Gibbsequation:

=

=

= x -7.8984 x 10-4= 0.3134 x 10-6 mol m-2

*The above calculation is applied to the amyl alcohol of different concentrations.From Graph 3, we can observe that the limiting value for the highest concentration is 6.9649 x 10-6 mol m-2. Avogadros number, NA = 6.022 x 1023 mol-1

Average surface area per molecule of amyl alcohol= 1/ ( maximum x NA)= 1/ (6.9649 x 10-6 mol m-2 x 6.022 x 1023 mol-1)= 2.3842 x 10-19 m2

Table 2: The surface tension, and for the different concentration of amyl alcohol.N-amyl alcohol concentration, c /mol dm-3

ln cSurface tension, ( 0.0001 ) Nm-1d/dlnC (10-3)mol m-2

123Average

0.01-4.60520.06100.06200.05850.0605-0.789840.3134

0.02-3.91200.05850.05950.06750.0585-4.810401.9086

0.04-3.21890.05600.05500.05400.0550-8.830383.5036

0.06-2.81340.05100.05100.04800.0500-11.182284.4367

0.08-2.52570.04500.04500.04350.0455-12.850945.0988

0.10-2.30260.04300.04350.04400.0435-14.144925.6122

0.15-1.89710.03650.03800.03650.0370-16.496826.5453

0.18-1.71480.03600.03350.03400.0345-17.554166.9649

0.20-1.60940.03350.03300.03200.0325-18.165487.2074

Graph of versus ln C for the amyl alcohol is showed in Graph 2Graph 2

Graph of versus concentration for amyl alcohol is showed in Graph 3Graph 3

Part 3: Measure surface tension of different concentration of t-butyl alcoholWeight of t-butyl alcohol used = (6.1770 0.0001) gMolecular weight of t-butyl alcohol = 74.12 g mol-1Concentration t-butyl alcohol that used for preparation

= x = 0.8334 mol dm-3By using M1V1 = M2V2where, M1 = Concentration of t-butyl alcohol V1 = Volume of solution =100 ml M2 = Concentration of stock t-butyl alcohol = 0.8334 mol dm-3 V2 = Volume of stock t-butyl alcohol used

For 0.5 ml t-butyl alcohol used,M1 x 100 ml = 0.8334 mol dm-3 x 0.5 ml M1 = 0.8334 mol dm-3 x 0.5 ml / 100 ml = 0.0042 mol dm-3

*The calculation above is used to calculate other concentrations of t-butyl alcohol

Example of calculation of and for t-butyl alcohol of different concentrations:By using the equation from Graph 4: y = -0.0011x2 - 0.0119x + 0.0389Assuming x = ln C y = = -0.0011 (ln C)2 - 0.0119 (ln C) + 0.0389

= -0.0022 ln C - 0.0119

Calculation of the 0.0042 mol dm-3 t-butyl alcohol

= -0.0022 ln C - 0.0119 = -0.0022 (-5.4727) - 0.0119 = 1.3994 x 10-4The value of for the concentration, C can be calculated by using adsorption Gibbsequation:

=

=

= x 1.3994 x 10-4 = -0.05552 x mol m-2

*The above calculation is applied to the n-amyl alcohol of different concentrations.

From Graph 5, we can observe that the limiting value for the highest concentration is 2.78117 x 10-6 mol m-2. Avogadros number, NA = 6.022 x 1023 mol-1

Average surface area per molecule of t-butyl alcohol= 1/ ( maximum x NA)= 1/ (2.78117 x 10-6 mol m-2 x 6.022 x 1023 mol-1)= 5.9708 x 10-19 m2

Table 3: The surface tension, and for the different concentration of t-butyl alcohol.t-butyl concentration, c / mol dm-3ln cSurface tension, ( 0.0001 ) Nm-1

123Average

0.0042-5.47270.07200.07150.07100.0715

0.0083-4.79150.07100.07000.07050.0705

0.0250-3.68890.06950.06750.06700.0680

0.0417-3.17730.06650.06550.06600.0660

0.0583-2.84220.06400.06300.06350.0635

0.0833-2.48530.06300.06300.06200.0625

0.1083-2.22290.06000.05900.05950.0595

Graph of versus ln C for the t-butyl alcohol is showed in Graph 4Graph 4

Graph of versus concentration for t-butyl alcohol is showed in Graph 5Graph 5

DISCUSSIONSGraph 1 shows that surface tension decrease when the number of carbon atoms per molecule increases, that is 1/n (n = number of atom carbon). The length of hydrophobic aliphatic chain increases whereas the number of hydrophilic group (-OH) still remained the same. The hydrophobic group, which has no affinity to water, will try to get rid of water molecule and adsorb on the surface of solvent. This phenomenon will influence the surface activity, which is inversely proportional to the surface tension. Thus, number of carbon atoms per molecule increases, results in a higher value of surface activity and a lower value of surface tension being obtained.The influence of concentration towards the surface tension, can be observed in graph 2 and graph 4, indicating surface tension or values decreases when the concentration of alcohol increases. As a result, the number of aliphatic alcohol chain adsorbed will increase too. Therefore, the surface activities increase when the surface tensions decrease. This can be represented by 1/c ( c = concentration of alcohol).From graph 3 and graph 5, we found that the limited value for amyl alcohol is higher than the limited value for t-butyl alcohol. maximum (amyl alcohol) = 6.9649 x 10-6 mol m-2 maximum (t-butyl alcohol) = 2.7812 x 10-6 mol m-2This shows that the amyl alcohols surface activity is higher than t-butyl alcohol. And the average surface area per molecule proves this:n-amyl alcohol = 0.238 nm2t-butyl alcohol = 0.597 nm2As the average surface area of n-amyl molecule is small, since the number of amyl molecule adsorbed are higher than t-butyl molecules. This is because the amyl alcohol is straight molecule whereas the t-butyl alcohol is a branch moleculeAccording to graph 3 and 5, limited value, , increases with the bulk concentration (both t-butyl alcohol and amyl alcohol). At first increases proportionally, then less rapidly as the concentration increases and the surface became full with adsorbed molecules. After values go to a maximum, it will start dropping whenever we increase the concentration because there are too many molecules present on the surface to form a mono layer. The thickness of the surface is assumed to be more than one layer, therefore the value is expected to be higher. Cross-section area for paraffin is given by 0.195cm2. This value is much higher than the average surface area for the two alcohols. Paraffin chain is a long hydrophobic chain. Therefore, it would not mix with water and forms a layer at the top of water. Paraffin chain prefers to arrange in horizontal at the surface whereas alcohol chain prefers to arrange in vertical with the hydrophilic group towards the water. As a result, the average surface area per molecule for paraffin is higher than the amyl alcohol and t-butyl alcohol. CONCLUSION1. When increase the number of carbon atom in alcohol, it will decrease the surface tension, results increase in surface activity. 2. When increasing of concentration of alcohol, it will decrease the surface tension, and resulting in increasing of surface activity.3. Limited value, , for amyl alcohol = 6.9649 x 10-6 mol m-24. Limited value, , for t-butyl alcohol = 2.7812 x 10-6 mol m-25. Average surface area per molecule for n-amyl alcohol = 0.238 nm26. Average surface area per molecule for t-butyl alcohol = 0.597 nm27. The surface activity of amyl alcohol is higher than t-butyl alcohol.

REFERENCES 1. Peter Atkins & Julio de Paula. Atkins Physical Chemistry (7th edition). Oxford University Press.2. Laboratory Manual, Year III, Department of Chemistry, University of Malaya, Session 08/09, pp. 48-50.

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