MEMORANDUM

TO: AHMED ASSEM

FROM: DEVON HILLMAN

PETE 311 – 503

SUBJECT:LAB NO 2: SURFACE/INTERFACIAL TENSION

DATE: SEPTEMBER 4, 2013

In this laboratory experiment, our main objective was to learn how to use a tensiometer in order to find surface and interfacial tension.

“On my honor as an Aggie, I have neither given nor received unauthorized aid on this academic work.”

[Signature of student]

Attachment(s): Lab report

Title: Lab 2: Surface/Interfacial Tension

Discussion and Results

For the first part of this experiment, the surface tension of water was found. Before we could begin, the

sample vessel and plate had to be thoroughly cleaned. After the plate was dried, the sample stage was

moved down, and the plate was hooked to the force sensor. Then we filled the sample vessel with water

and placed it on the sample stage. Once we checked and made sure the parameters were correct, we

moved the sample stage upward until the hanging plate was just above the surface of the liquid. Then we

pressed “Tare” so that the weight of the plate displayed 0.0 g. Then we pressed “Surface detect” in order

to move the sample stage upward until the surface of the liquid was in contact with the hanging plate. We

rotated the inner ring on the height adjustment knob so that the marking was even with the zero position,

and then rotated the height adjustment knob so that the hanging plate was immersed to a depth of about 3

mm. After the motor controls were used to return the sample stage where the marking of the drag pointer

was at zero again, we pressed “Start” to measure the surface tension of the water. Once the mean value of

the tension was found, we recorded it and then cleaned the sample vessel and the hanging plate in order to

continue with the experiment. To find the surface tension of kerosene, we filled the sample vessel with

kerosene and then repeated the steps above. For interfacial tension the process was a little different. We

hung the cleaned plate from the force sensor and put the cleaned sample vessel filled with kerosene onto

the sample stage. We then checked the parameters to make sure they were correct and then moved the

sample stage upward until the hanging plate was completely immersed in the kerosene. Then we pressed

“Tare” so that the weight of the plate displayed 0.0 g. After that, we removed the sample vessel filled

with kerosene and then carefully removed the hanging plate to clean and dry them. Once the sample

vessel is dry we filled a third of it with water and replaced it on the sample stage and rehooked the plate

to the force sensor. We then moved the stage up until the plate was just above the surface of the water

and pressed “Surface detect”. We rotated the inner ring on the height adjustment knob so that the

marking of the drag pointer was at zero again, and then rotated the height adjustment knob so that the

hanging plate was immersed to a depth of about 3 mm. Then we carefully added kerosene to the sample,

returned the sample stage to the point where the drag pointer was again at zero, and pressed “Start” to

measure the interfacial tension. Once we the mean value of the interfacial tension was found, we

recorded it and cleaned up our area. The values for the surface tension of water and kerosene and the

interfacial tension between water and kerosene are shown below in Table 1.

Table 1 – Surface and interfacial tension of water and kerosene.

Liquid Surface Tension Interfacial Tension

Water 70.6 mN/m

Kerosene 24.6 mN/m

Water & Kerosene 64.3 mN/m

Conclusion

In summary, this lab taught me the difference between surface and interfacial tension, how to use a

tensiometer, and that patience is needed in the laboratory. I learned really quickly that the tensiometer is

a very sensitive machine. During our experiment, we had to repeat the interfacial tension test three times

because the machine was sensitive to our movements. This could be why our value of 64.3 mN/m for the

interfacial tension is off. A more accurate value for the interfacial tension between water and kerosene

would be between 50 – 55 mN/m.