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KWAME NKRUMAH UNIVERSITY OF SCIENCE AND
DEPARTMENT OF CHEMISTRY
YEAR TWO (CHEM 270)
PRACTICAL CHEMISTRY IV
TITLE: SURFACE TENSION
NAME: OPOKU ERNEST
DATE: 14TH MARCH, 2014
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AIMS AND OBJECTIVES
1. To enable students familiarize themselves with how the tensiometer is used
2. To determine the surface tension of different alcohol liquids
Surface tension is the property of a liquid in contact with air or vapour that
makes it behaves as if it were covered with a thin membrane under tension. For
example if you were to fill a glass of water and carefully place a thin razor blade
onto the top of the water, it would float for a short time due to this pseudo-
membrane that support it. This ``tension`` at the surface results from
intermolecular forces within the solution that cause the exposed surface to
contract to the smallest possible area. This is because a molecule in the interior
of the solution interacts with other molecules equally from all sides, where as a
molecule at the surface of the liquid is only affected by the molecules below it.
This property of surface tension is responsible for formation of liquid droplets,
soap bubbles, and menisci (the curved upward or downward appearance of a
column of liquid).
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Surface tension is defined as the force acting over the surface of a solution per
unit length of the surface perpendicular to the force. It is usually measured in
dynes per centimeter. The SI unit is Newton per meter.
Let consider these two setups a and b.
(a) A molecule within the bulk liquid is surrounded on all sides by other
molecules which attract it equally in all directions leading to zero net
(b) A molecule in the surface experiences a net attractive force point
towards the liquid interior, because there no molecules of the liquid
above the surface.
In this experiment this phenomenon would be employed to determine the surface
tension of the various alcohol prepared. The measurement would be done with
Du Nouy Ring Tensiometer.
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This type of tensiometer uses a platinum ring which is submersed in a liquid.
As the ring is pulled out of the liquid, the tension required is precisely measured
in order to determine the surface tension of the liquid. This method requires that
the platinum ring be nearly perfect; even a small blemish or scratch can greatly
alter the accuracy of the results. A correction for buoyancy must be made. This
method is considered inaccurate compared to the plate method but is still widely
used for interfacial tension measurement between two liquids.
Du Nouy tensiometer in liquid uses a platinum ring which is submersed in a
liquid. As the ring is pulled out of the liquid, the tension required is precisely
measured in order to determine the surface tension of the liquid. This method
requires that the platinum ring be nearly perfect; even a small blemish or scratch
can greatly alter the accuracy of the results. A correction for buoyancy must be
made. This method is considered inaccurate compared to the plate method but is
still widely used for interfacial tension measurement between two liquids.
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Du Noüy Ring Tensiometer
Du Noüy-Padday method, This method uses a rod which is lowered into a test
liquid. The rod is then pulled out of the liquid and the force required to pull the
rod is precisely measured. This is a rather novel method which is accurate and
repeatable. The Du Noüy-Padday Rod Pull Tensiometer will take measurements
quickly and unlike the ring and plate methods, will work with liquids with a wide
range of viscosities.
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Application of Surface and interfacial tension measurements are extremely
important in the control and improvement of: absorption cataphoresis
condensation emulsification evaporation miscibility osmotic pressure solubility.
CHEMICALS AND APPARATUS
1. Methyl alcohol
2. Ethyl alcohol
3. N- propyl alcohol
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4. N-butyl alcohol
5. Amyl alcohol
6. Du Nouy ring tensiometer
7. 100ml volumetric flasks
8. Pipette ( with disposable tips)
1. Pipette (each alcohol was assigned to one disposable tip) a specified
volume of the alcohol as stated below.
Alcohol Volume measured/ml
Methyl alcohol 0.40
Ethyl alcohol 0.58
n-propyl alcohol 0.75
n-butyl alcohol 0.92
Amyl alcohol 1.08
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2. The measured volume was then diluted to 100ml to make up a
concentration of 0.1M and the surface tension determined using Du Nouy
3. The surface tensions of the following Molar (M) of amyl alcohol were
determined using the Du Nouy tensiometer 0.01, 0.02, 0.04, 0.06 and 0.10.
TABLE OF RESULTS
Alcohol Surface tension in mJm-2
Methyl alcohol (MeOH) 68.0
Ethyl alcohol (EtOH) 63.0
n-Propyl alcohol (n-PrOH) 62.0
n-Butyl alcohol (n-BuOH) 59.0
Amyl alcohol (AmOH) 54.0
Amyl alcohol in Molar Volume measured Surface tension
0.01 0.108 20.0
0.02 0.216 55.0
0.04 0.432 52.0
0.06 0.648 48.0
0.10 1.080 54.0
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0 1 2 3 4 5 6
NUMBER OF CARBON ATOM IN ALCOHOL
0 0.02 0.04 0.06 0.08 0.1 0.12
CONCENTRATION OF AMYL ALCOHOL
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Slopes of the alcohol (number of carbon)
Number of carbon Slope
Slopes of amyl alcohol
Concentration of amyl alcohols Slope
T(C) = C X slope for number of carbon
T(C1) = 0.1 x 6.67 = 2.692 x 10-4
= 0.1 x 13.33 = 5.38 x 10-4
= 0.1 x 3.33 = 1.344 x 10-4
= 0.1 x 5.00 = 2.018 x 10-4
= 0.1 x 8.75 = 3.531 x 10-4
T(C) = C X slope for concentration
= 0.010 x 2500 = 1.009 x 10-2
= 0.020 x 218.75 = 1.77 x 10-3
= 0.040 x -333.33 = -5.38 x 10-3
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= 0. 060 x 333.33 = 8.072 x 10-3
= 0.100 x 500= 2.018 x 10-2
It could be observed from the graph that surface tension against number of
carbons of the alcohol decreases as the number increases. This could accounted
for the reason being that as the number of carbon increases the entropy level of
the solution increases therefore limiting its elastic ability.
For the other graph of surface tension against concentration of amyl alcohol, the
surface tension decreases as the concentration of the amyl alcohol increases. The
number of molecules interacting in the solution increases therefore disturbing the
1. The ring of the tensiometer should not be touched with the fingers.
2. The tensiometer was standardized with cold water.
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3. The experiment was assumed to have been done under an ideal condition,
which is the room temperature was assumed to be 25o
The goals of the experiment were achieved. It is known that as the number of
carbons increases, surface tension also decreases. For the amyl alcohol, as it
concentration increases it surface tension also decreases.
1. `Experimental physical chemistry` Daniels, William and others pg 321-328
2. Chemical Technician Ready Reference Handbook 2nd
edition by Shugar
and Bauman pages 592- 593
3. Textbook of Practical Chemistry 4th
edition (2001) by Wesley. D. Smith
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