Transcript
Surface Tension of Solutions
Student name:
Student number:
Lab partner:
CHE 214, Section 02
February 11, 2013
TA:
Introduction and Background
Intermolecular forces are one of the factors that are responsible for the Surface tension phenomenon. Surface tension occur as the molecules at the surface of the liquid such water attract each other. The interrelated attraction force pulls the molecules at the liquid surface towards each other and thus causing a surface tensions phenomenon. However, molecules at the surface of water are subjected to a strong intermolecular force and hence attract molecules that are around and below the surface. While on the surface, liquid molecules attract with their neighbourhood atom only (molecules that are nearby them). Viscosity of the liquid is another factor that is responsible for surface tensions, the higher the viscosity, hence the stronger intermolecular force between the molecules. Also, the surface tension is inversely proportional to the temperature, as the temperature increase the surface tension decreases. Thus, the purpose of this lab was to determine experimentally the surface tensions of solutions using thermometer and tensiometer (a device that measures the surface tension of the liquid at correct contact angle). Therefore, this lab divided into two parts.
Firstly, the surface tension of the water and alcohol solutions of 0.2 M (ethanol, 1-propanol, 1- butanol, 1- pentanol) had measured using Tensiometer. However, the water and alcohols scale reading surface tensions were recorded as the solutions on the sample table lowered using adjustment screw, when a wetted ring was left slowly from the solutions and caused a break in the surface tensions of the solutions .The correction scale surface tensions of the five solutions at different temperature measurement were calculated as using the formula shown below;
F = Literature Value/ experiment Value
Where: F is the correction surface tensions factor
Secondly, the surface tensions of n-butanol of different concentrations (increasing order) ranging from (0.1-0.8M) measured in the same way as the five solutions in part one. For each solutions three reading of temperature and surface tension had been taken in order to obtain an accurate result. Finally, the access surface tension was computed in order to estimate the effective cross-sectional area of adsorbed butanol using the equations below;
u= -1/RT * dy/d (lnC)
Where: u is the access surface tension in mol/m2
R is the gas constant
T is the absolute temperature in K
In conclusion, to all the formulas shown above, the graph, result, observation and calculation will demonstrate each one in their own way.
Result and Calculations
Calculations of part a:
*All the literature surface tensions had been recorded from the CRC handbook.
Part A: Table1. Surface Tensions of the Lower Aliphatic Alcohols at Different Temperature Scale
Solutions
Trail #
Temperature
Reading oC
Averg. Temperatue oC
Surface Tension Scale Reading
Aveg. of Surface tension
F corrections
Corrected Surface Tensions
Water
1
20.5
20.5
50.9
50.9
1.4
72.29
2
20.5
50.9
1.4
3
20.6
50.8
1.33
Ethanol (0.2M)
1
20.5
20.5
48.1
48.5
0.46
68.87
2
20.5
48.9
0.46
3
20.4
48.4
0.46
1-propanol (0.2M)
1
21.2
21.1
43.9
42.8
0.538
60.78
2
21.1
41.9
0.569
3
21.1
42.5
0.561
1-butanol (0.2M)
1
33.0
33.9
20.5
20.4
1.142
28.97
2
34.5
20.5
1.148
3
34.1
20.3
1.158
1-pentanol (0.2M)
1
21.1
21.2
23.0
23
1.145
32.66
2
21.1
22.9
1.150
3
21.3
23.0
1.146
The F correction for the Surface Tension of the solutions was calculated as shown below:
The literature value for the surface tension of water at 20.5oC was obtained from the CRC handbook. However, Calibration factor for the brown tensiometer = 1.42
F correction for Water = Literature Value/ experiment Value
= 72.75/50.9 F correction for Water = 1.4
F correction of water = surface tension * calibration Factor of brown tensiometer
= 50.9*1.42
= 72.29
The literature values for the surface tension of alcohol at different temperature was obtained from the CRC handbook
Ethanol
The literature value for 20.5oC and 20.4oC was computed by interpolating the temperature and the literature value as shown below:
Temperature (20.5 oC) literature value
10 x1 23.22 y1
20.5 x y=?
25 x2 21.97 y2
y=y1+ [(x-x1)/(x2-x1)] x (y2-y1)
= 23.22+ [(20.5-10)/ (25-10)] x (21.97-23.22)
= 22.35
F correction for ethanol = Literature Value/ experiment Value
= 22.35/48.1 F correction for ethanol = 0.46
The same method was calculated for the literature value of ethanol at 20.4oC.
F correction of ethanol = surface tension* calibration Factor of brown tesnsiometer
= 48.5*1.42
= 68.87
1-propanol
The literature value for the three temperature reading was computed by interpolating the temperature and the literature value as shown for trail #1 (21.2oC ) below:
Temperature (20.5 oC) literature value
10 x1 24.48 y1
21.2 x y=?
25 x2 23.32 y2
y=y1+ [(x-x1)/(x2-x1)] x (y2-y1)
= 24.48 + [(21.2-10)/ (25-10)] x (23.32 -24.48)
= 23.61
F correction for propanol = Literature Value/ experiment Value
= 23.61/43.9 F correction = 0.538
F correction of propanol = surface tension* calibration Factor of brown tesnsiometer
= 42.8*1.42
= 60.78
1-butanol
The literature value for the three temperature reading was computed by interpolating the temperature and the literature value as shown for trail #1 (33oC ) below:
Temperature (20.5 oC) literature value
25 x1 24.93 y1
33.0 x y=?
50 x2 22.69 y2
y=y1+ [(x-x1)/(x2-x1)] x (y2-y1)
= 24.93 + [(33-25)/ (50-25)] x (22.69 -24.93)
= 23.41
F correction for butanol = Literature Value/ experiment Value
= 23.41/20.5 F correction = 1.142
F correction of butanol = surface tension* calibration Factor of brown tesnsiometer
= 20.4*1.42
= 28.97
1-pentanol
The literature value for the three temperature reading was computed by interpolating the temperature and the literature value as shown for trail #1 (21.1oC ) below:
Temperature (20.5 oC) literature value
10 x1 26.67 y1
21.1 x y=?
25 x2 25.36 y2
y=y1+ [(x-x1)/(x2-x1)] x (y2-y1)
= 26.67 + [(21.1-10)/ (25-10)] x (25.36 -26.67)
= 26.33
F correction for pentanol = Literature Value/ experiment Value
= 26.33/23 F correction = 1.145
F correction of pentanol = surface tension* calibration Factor of brown tesnsiometer
= 23*1.42
= 32.66
Calculation of part b):
The calibration factor for the blue tensiometer =1.33
Part B: Table2. Surface Tensions of Various Concentrations of n-butanol at Different Temperature Scale
1-butanol Solutions of Various Conc.
Trail #
Temperature Reading oC
Averg. Temperature oC
Surface Tension Scale Reading
Averg. value of surface Tensions
F corrections
0.1M
1
19.8
20
44.3
44.1
58.65
2
20.0
44.0
3
20.1
44.0
0.3M
1
20.3
20.3
34.0
31.6
42.03
2
20.3
29.8
3
20.3
31.0
0.4 M
1
20.7
20.6
28.0
28.0
39.76
2
20.6
28.0
3
20.6
28.1
0.5M
1
20.8
20.8
25.9
25.8
36.64
2
20.8
25.8
3
20.7
25.7
0.6M
1
21.0
21.0
25.0
25.0
35.5
2
21.0
25.0
3
21.1
25.1
0.7M
1
20.0
20.0
23.0
22.9
30.46
2
20.0
22.9
3
20.0
22.8
0.8M
1
20.2
20.2
22.5
22.6
30.06
2
20.2
22.8
3
20.1
22.6
Q1) Plot a graph of Surface tension versus alcohol chain length (including water as chain length of 0).
Graph1. Surface tension and the alcohol carbon chain length.
Q2) For the 1-butanol solutions, plot graph of surface tension against bulk consternation.
Graph2. Surface Tension and 1-butanol Solutions of Various Concentration
Q3) For the same solutions, plot surface tension against the ln of the bulk concentration and determine the slop of the linear portion. Calculate the excess surface concentration u in mole per square metre using Equation 5.4.
Graph 3) Surface Tensions and the ln of 1-butanol of various Concentrations ranging (0.1-0.8M)
The equations below showing the calculation for the access surface tension and effective cross-sectional area respectively from graphs #3:
R= 18.314 m3. Pa / k. mol
T= 20oC+273.15
= 293.15 K
u= -1/RT * dy/d (lnC)
= 1/ (8.314*293.15) * (-1.3515*10-2)
= 5.55x10-6 mol/m2
28098755111751247775511175Q4) Convert u into units of molecules per square nanometer and from this estimates the ‘effective cross- sectional area’ per molecules of adsorbed butanol in square nanometers.
5.55x10-6 mol 6.022 x 1023 molecules 1m2
m2 1mol (109nm)2
u= 3.34 molecules/nm2
Discussion
The purpose of this experiment was to determine the effect and the relationship between temperature, intermolecular forces, and molecules chemical structure (carbon chain length) with surface tensions. The first part of this experiment was to compute the surface tension of water at different room temperature of (20.5oC and 20.6oC). Three surface tensions reading scale values of water and alcohols were observed and rescored using tensiometer as the surface of the water and an alcohol increased and thus breaks. Water is polar molecules; therefore, molecules are bonded and attracted to each other because of the strong intermolecular forces (OH- bond). Hence, water had surface tensions higher than alcohol as shown in table1 above because alcohol molecules have C-H which is non-polar comparing with water hydrogen bond (O-H). However, the molecule structure of alcohol has the effect on increasing or decreasing the surface tensions. For example, 0.2 M ethanol has surface tension (48.5 dyne/cm) while 1-pentanol of (0.2M) has surface tensions of (23 dyne/cm) which indicate that the surface tension decrease as the number of carbons increasing due to increasing the non-polar bond C-H. Otherwise, as the alcohol carbons chain length increasing, the surface tension of the solutions will decrease because of the weak attractions between molecules London Depression intermolecular forces in C-H carbon chain bond.
However, the n-butanol had been measured in order of increasing order to shown the effect and the relationship of the concentration of 1-butanol on the surface tension. In the second part of the lab, the surface tensions of 1-butanol of various concentrations had been measured using tensiometer. As the concentration of the 1-butanol increased the surface tensions decrease this is way the butanol solutions measured in increasing order rather than randomly. For instance, the surface tension of 0.1 M 1-butanol was (44.1 dyne/cm) while the surface tension of 0.8 M 1-butanol was (22.6 dyne/cm) that showed that the surface tensions of alcohols (n-butanol) are inversely proportional with the concentration of the solutions. The value of 1-butanol on the graph 2 at the lowest concentrations equals to the water concentrations at which is (7 dynes/cm). The butanol molecules are oriented perpendicular because of the molecules shapes since butanol molecules has an OH bond and CH bond on the carbon chain so it react with water molecules and bent to approximately to angle of 79o. The dimensions of molecular effective cross-sectional area of adsorbed butanol are measured in mol/m2. However, the increases in excess concentration have no effect on the bulk concentration of the solutions.
Water droplet tend to bead on a freshly waxed car cause freshly wax is non-polar and has low surface tension comparing with water that has a higher surface tension (polar)therefore, molecules attract each other and thus lower the intermolecular forcer and the surface area per unit volume . However, dirty wax has higher surface tension (polar) so as it attract with water molecular with high surface tension and polar molecules it oxidise and hence the was layer will worn off. The source of error that observed in the experiment was little bit high for many reasons. Firstly, the index of the tensiometer was not aligned properly at zero which caused error in reading the surface tensions. Also, the sample table was lowered rapidly that in return caused some error when recording and measuring the surface tension of the solutions.
Conclusions
Liquid molecules at the surface of the water attract each other as a result of a strong intermolecular force between the molecules which caused a surface tension phenomenon. There are many factors that contribute in causing a surface tension in a liquid such temperature, viscosity, intermolecular forces, a chemical structure of the molecules and concentrations. Since water is polar molecules, the attraction between the molecules are strong OH bond. Alcohol; however, has a low intermolecular forces and thus low surface intension since the attraction between alcohol molecules (CH non-polar bond) are weak. Temperature has an effect on the surface tension since the surface tension is inversely propositional with the temperature. That concludes that the surface tension of pure solvent is completely different form organic solutions due to the molecules attractions forces.
References:
The 92st edition of the CRC Handbook of Chemistry and Physics, 2011-2012
ACS Chemistry for Life, Middle School Chemistry-Surface Tensions, American Chemistry, 2013, page 979-983. http://www.middleschoolchemistry.com/lessonplans/chapter5/lesson2
Surface Tensions, Academic Press, 2006
http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html
Thermodynamics II (Surface Tension of Solutions ) lab manual
