TENSION
BREAKER
The effect of temperature on the surface tension of
water compared to oil
By Meg Lonie
Mr. Hook 8.1
Abstract
In my project I explored how temperature affects the surface tension of liquids. I
also compared the average surface tension of water in comparison to olive oil. I
recorded over 60 results of water and olive oil with temperatures ranging from 5100°C. This was tested by a homemade apparatus, which had a balanced beam with
a needle on one end and a cup on the other. The cup’s purpose was to hold the rice
grains that were individually placed in, while the needle’s purpose was to float on
the surface of the water. Once the needle broke away from the surface the tension
was broken and I recorded the temperature and number of grains needed. Through
these experiments I found that the as temperature increased surface tension
decreased and that the surface tension of water is higher than that of oil.
Introduction
Topic Importance and Choice
Surface tension is a crucial scientific discovery, which allows us to predict how liquids
will act in certain situations. Surface tension is important to understand as it is used
in many areas of everyday life. In my experiment I am focusing on the effect that the
temperature of water or olive oil has on its surface tension and I will be comparing
the two sets of results to find which liquid on average, has the highest surface
tension.
Surface tension involves the molecules of a liquid binding together to form a “skin”.
In order to use a liquid it is sometimes necessary to manipulate the surface tension,
and it is therefore important to understand the science behind it. An example of
utilising surface tension is seen in the design of tents. The material, which a tent is
made from, is designed to keep water out. The surface tension of water helps to seal
the pores of the woven fabric, thus keeping out rain. However if you touch the
material the surface tension breaks and rain can drip through. An example of when
surface tension needs to be broken is when washing your hands. Soap is often used
here to break the surface tension as it is a surfactant (a material which reduces
surface tension), and therefore it can seep into your skin to clean properly.
Surface Tension
Surface tension is caused by the attraction of the molecules in a liquid. Each
molecule is pulled equally in all directions by molecules next to it. However, at the
surface of the liquid, other molecules inside the liquid pull the molecules inwards. As
there are no liquid molecules on the outside to balance these forces, there is only an
inward force; this force causes tension on these particles. Surface tension sometimes
gives liquids the appearance of having
a transparent ‘skin’.
Diagram of Surface Tension
The surface tension of water or oil is not very strong, however, it is strong enough to
stop light objects from falling through. For example a needle can float on the
surface.
With any liquid, the higher the temperature, the lower its surface tension will be.
This is because, as the liquid cools the molecules move slower, and it takes more
energy to break through them. Think of it as though the colder the liquid is, the
closer it is to becoming a solid and freezing. If frozen the surface is hard and cannot
be broken.
Cold Liquid
Hot Liquid
Movement of Liquid Molecules
When comparing oil to water, water has the greatest surface tension. This is due to
the greater force between water molecules compared to those of olive oil.
Surface tension and viscosity both involve properties of liquids. While surface
tension relates to the internal forces pulling molecules toward the main part of the
liquid, viscosity is the liquid’s resistance to flow. With the same amount of two
liquids, the liquid, which takes the longest to flow, has the higher viscosity.
Oil has a higher viscosity than water. Surface tension and viscosity are both
characteristics of liquids but they do not relate to each other. Many people think
that thicker or more viscous liquids would also have a higher surface tension,
however this is not always the case.
Direction of Flow
Liquid
Molecule
Viscosity Force
The effect of the force of viscosity on the flow of a liquid molecule
Conclusion
In this project I wanted to determine if, and how temperature affects surface tension
of water and oil. I also wanted to compare the surface tension of oil and water and
determine which is higher. I chose this project, as it is a relevant and useful
experiment, which can be applied to my own life. Surface tension is used all the
time, and it is important to understand how liquids behave.
Aim
To investigate the affect, which temperature has on surface tension of water
compared to the surface tension of oil.
Hypothesis
1. Effect of Temperature on Surface Tension
If the surface tension is related to the temperature of the liquid, then liquids at
higher temperatures will have lower surface tension, and liquids at a lower
temperature will have a higher surface tension. This is because the higher the
temperature of the liquid the more the molecules move around, thus breaking the
surface tension.
2. Comparison of Oil and Water
If the surface tension of a liquid is related to the liquid being measured then the
surface tension of olive oil will be higher than that of water. This is because oil has a
higher viscosity than water.
Materials and Methods
Apparatus Construction
Materials for construction:
 Saw
 Base wood
 2x side wood pieces
 2x metal brackets
 8x screws
 Screw driver
 Drill
 Dowel wood (13cm x 1.4cm x 1.4cm)
 2x rotating screws
 Wedged wood (15cm x 2cm x 4cm)
 Coat hanger (wire)
 2x string (22cm)
 Needle /nail
 Bottle cap
 Sewing needle
 Blue tack
 Glue
Method for Apparatus Construction
1. Using a saw cut a plank of wood to form the base (15cm x 4cm x 4cm)
and then cut to form the two sides (37cm x 7cm x 3.5cm).
2. Drill holes of 6mm wide and 1.5cm deep at the top, in the middle of each
sidepiece of wood.
3. Position the base so that it is flat on the ground with the sides attached
to either end to form a “U” shape. Ensure the holes are facing inwards
and are at the top of the sides.
4. Attach each of the sides to the base using brackets. Position the brackets
inside the “U” on both sides and screw them in using a screwdriver.
5. Hammer nails into each end of the dowel wood, up until the stopper on
the nails, about 1.5cm of the nail should not be hammered in.
6. Place each end of the dowel or the nails into the two holes in the vertical
pieces of wood, to hold the dowel in place.
7. Drill a hole of about 3mm through the middle of the dowel using a drill.
8. Using wire cutters cut a coat hanger just after the corners. Slot the wire
through the hole to act as a tilting beam.
9. Tie a piece of string to the needle/nail and then one end of the beam.
10. Push the end of a sewing needle through the plastic to create a whole.
Repeat four times until there are holes equally positioned.
11. Thread a piece of string from the inside of the cap through a hole to the
outside, holding onto the end. Then thread it from the outside to the
inside and then tie the two ends together. Repeat on the other holes, and
then tie the two pieces together and string over the other end of the
wire.
12. Wedge a piece of wood between the vertical pieces to ensure they are
parallel.
13. Glue the hole in the dowel up, to stop the wire from sliding around and
let it dry overnight.
14. Add the blue tack as a weight to one side of the wire if necessary.
Testing Surface Tension Experiment
Materials for the Experiment:
 Electronic thermometer
 Glass
 Whiteboard marker
 Bull clip
 Basmati rice
 Tweezers
 Kettle
 Ice
 Water
 Olive oil
Method for Experiment
1. Use a bull clip, and attach the wire of the thermometer to the side of the
glass with the sensor inside.
2. Level the wire, and mark the spot where the needle hangs on the glass
using a whiteboard marker.
3. Pour or oil into the glass up to the marked line and place it under the
hanging needle, so the needle is just on the surface of the liquid.
4. Check the temperature of the liquid and record.
5. Place grains of rice individually into the bottle cap using tweezers,
counting how many are needed.
6. Continue until the needle breaks away from the surface of the water or
oil and the cap filled with rice tips the balance.
7.
Repeat experiment for temperatures ranging from
Apparatus Diagrams about 5-90°C.
Risk Assessment
Risk
Hot water or oil is a
potential burn hazard,
which could cause
scalding.
Using the drill or
electronic saw while
making the apparatus
could cause cuts.
Splinters from the wood
could cause bleeding and
possible infections
Precaution
Parental supervision when handling and pouring hot
liquids, wearing safety gear (gloves, enclosed shoes)
and keeping any hot water or oil jugs away from the
edge of the table in case they are knocked off.
Wearing glasses while cutting wood to prevent wood
shavings from getting in my eyes, wearing gloves when
using the drill and saw and having parental supervision
at all times to ensure my safety.
I will sand any sharp edges of the wood and wear gloves
when handling and cutting the wood.
Variables
For my experiment to be accurate I have to identify the variables, which will affect
the outcome. They will need to either be changed, kept constant or controlled.
Independent Variable: Temperature of the water or oil
Dependent Variable: Surface tension
Controlled Variables: Liquid depth, floating object, length of the string, type of rice,
air movement and pressure.
Controlling Variables
Variable
Liquid depth
Method to Control the Variable
To control the liquid’s depth I will have drawn a line on
the glass with a marker. This is where the liquid should
be filled up to for every experiment. I measured this on
the glass by where the needle hung when the
apparatus was balanced. This depth will be kept the
same for both water and oil experiments.
Floating object
Length of string
Type of Rice
Air Movement and Pressure
To control the variable of the floating object I am using
the same object for all the experiments. The needle will
be tied to the string and kept controlled throughout.
This means the size and weigh will remain mostly the
same for all the experiments.
To control the variable of the string’s length I measured
the length of both strings, on each side. I then tied
them so that the lengths were both 22cm.
It is important to keep the type of rice the same for all
the experiments so that the results are accurate. The
type of rice I used for all my experiments was Basmati
Rice, I also monitored the size of each grain and
ensured all the rice grains I used to measure were
whole grains.
The air pressure could have influenced the surface
tension and the air movement could have influenced
when the needle or liquid moved. It was important for
these variables to be controlled so that there were no
invalid results provided. To control these I did all the
experiments in the same location and on the same day.
They were all completed inside so there was no outside
forces and within 3 hours.
Results
Water Surface Tension Results
The tables show the temperature of the water and the amount of rice grains needed
to break the surface tension, and pull the needle out of the water. The observations
are grouped according to temperature ranges of 10°C, and all results are recorded in
the tables.
Results from 5-15°C
Temperature (°C)
5.6
7.9
8.2
9.3
12.7
13.9
15.0
Grains of Rice
20
20
19
18
16
17
17
Results from 15-25°C
Temperature (°C)
16.3
17.8
18.0
20.2
22.7
24.6
Grains of Rice
17
17
17
15
16
15
Results from 25-35°C
Temperature (°C)
26.8
27.1
28.3
Grains of Rice
16
15
16
29.4
31.0
33.8
34.9
Results from 35-45°C
15
14
13
13
Temperature (°C)
36.4
37.8
38.3
39.8
41.9
42.6
43.7
44.4
Grains of Rice
13
13
12
13
12
11
11
11
Results from 45-55°C
Temperature (°C)
45.5
47.8
48.7
49.3
52.0
53.2
54.6
Grains of Rice
10
11
10
10
10
9
9
Results from 55-65°C
Temperature (°C)
55.5
56.2
57.9
59.0
60.5
63.2
64.7
Results from 65-75°C
Grains of Rice
10
9
9
8
9
8
8
Temperature (°C)
66.5
67.7
68.4
70.8
72.2
74.1
Grains of Rice
8
8
8
7
7
7
Results from 75°C +
Temperature (°C)
76.7
81.4
86.2
89.0
90.3
98.2
Grains of Rice
7
7
7
7
6
6
Effect of Temperature on Water Surface Tension
25
20
Grains of Rice
15
10
5
0
0
20
40
60
Temperature (°C)
80
100
120
Oil Surface Tension Results
The table below shows the temperature of the oil and the amount of rice grains
needed to break the surface tension, and pull the needle out of the oil. The
observations are summarized and visually represented in the graph, with a trend
line, which shows the average movement of the results. The results reveal that as
temperature increases the surface tension of the oil decreases, as it can be broken
with less weight.
Results from Oil
Temperature (°C)
35.2
47.5
56.6
66.0
78.3
89.4
Grains of Rice
12
10
9
8
6
6
Effect of Temperature on Oil Surface
Tension
14
Grains of Rice
12
10
8
6
4
2
0
0
20
40
60
Temperature (°C)
80
100
Comparison
All findings are summarized in this graph, which compares the results from oil and
water. All results are plotted, with the water as blue and the oil as red. Trend lines
are used for both to clearly show the relationship between temperature and surface
tension. This graph shows that in comparison to oil, water surface tension is
generally higher, and on average it takes more weight to break the surface of water
than it does to break the surface tension of oil at the same temperature.
Comparison of the Effect of Temperature on the
Surace Tension of Oil and Water
25
20
Grains of Rice
Water Surface
Tension
Oil Surface
Tension
15
Expon. (Water
Surface
Tension)
Expon. (Oil
Surface
Tension)
10
5
0
0
20
40
60
Temperature (°C)
80
100
120
Photos
Apparatus Diagram
Wire beam
Dowel
Thermometer
Sensor
Bracket
Needle
Base
Wood
Liquid
Cup for
rice
grains
Side
Thermometer
display screen
Discussion
Results
My results show the clear relationship between temperature and surface tension.
They imply that when the temperature of a liquid is increased its surface tension
decreases, and when the temperature of a liquid decreases its surface tension
increases. This information was displayed in the trend line on the graph which
showed the rising temperature as the weight required to break the tension
decreased.
This proves my first hypothesis for the effect of temperature on surface tension that
“If the surface tension is related to the temperature of the liquid, then liquids at
higher temperatures will have lower surface tension, and liquids at a lower
temperature will have a higher surface tension. This is because the higher the
temperature of the liquid the more the molecules move around, thus breaking the
surface tension.”
The last set of results and the graph showed that the surface tension of oil is much
lower than that of water. The oil trend line had lower averages of rice grains needed
to break the surface tension, than the trend line of water. This means it took less
weight to lift the needle out of the oil than it did to lift it out of the water at the
same temperature. While the effect of temperature on surface tension remained the
same on both proving that as temperature increases surface tension decreases, the
average surface tension of oil is lower than that of water.
This disproves my second hypothesis that “If the surface tension of a liquid is related
to the liquid being measured then the surface tension of olive oil will be higher than
that of water. This is because oil has a higher viscosity than water.”
My hypothesis was incorrect as the evidence I used was the comparison of oil and
water viscosity, which stated that oil’s viscosity was higher than that of water. While
viscosity and surface tension are both properties of liquids they do not relate at all.
When writing my hypothesis I thought that the thicker or more viscous liquid the
higher it’s surface tension would be. This is incorrect however as it completely relies
on the type of liquid as to it’s surface tension.
The results I obtained clearly showed that with increase in temperature surface
tension decreases. This was correlated with my research material, and proved my
first hypothesis to be true. The other results I obtained clearly showed that on
average water has a higher surface tension than oil. This correlated with my research
material, but proved my second hypothesis to be false.
There were a couple of results, which did not fit with the others. This was as a result
of certain errors, which occurred during measurements. These are outlined below in
the evaluation of my experiment.
Evaluation
To minimize the risk of errors I completed multiple tests. For each temperature
range of 10°C I had around 7 results and overall I had 54 measurements for the
water. It was important in my water experiment to use this large sample size so that
my results were as accurate as possible and if any errors occurred they would not
have a large impact on my overall results. Another benefit of completing multiple
measurements was that the results could easily be interpreted using a trend line. To
improve the reliability of my overall results including those on oil and water I would
have liked to complete more experiments on oil.
An important factor, which could have potentially influenced my results, was the
sizes of the rice grains. While there may only be slight differences in millimeters this
can have a biased effect on the results. As the surface tension is very exact and
delicate even the smallest difference in sizing could cause the results to appear
differently and provide incorrect readings.
A key area of concern was in the balance and weighting of the apparatus. The main
problem with this was that the beam would not allow for the needle to swing up,
which would mean the results would not be accurate. After trialing many different
methods to balance the sides equally I decided to use blue tack as a weight on one
side and a piece of wedged wood to separate the wooden sides and allow the beam
to swing smoothly. This solution worked well, meaning the beam was free to swing
and the sides were balanced, which meant accurate results could be obtained.
A problem, which I noted in my practices of the experiment, was that the depth of
the liquids had to be the same, so that the needle was always resting at the same
height. To solve this problem I balanced the apparatus so that the needle and the
cup were each the same height from the table. Then, using a marker I drew a line on
glass where the needle hung. This line would be the level to which I filled my glass
each time to insure a controlled depth.
The submersion of needle was an important factor in my measurements. The results
varied depending on where the needle was positioned in the water or oil. For
example, if the needle was under the surface by a few millimeters in one
experiment, and in the next it was sitting on the surface, the distance and resistance
on each needle would be different, therefore providing incorrect results. After
assessing this problem I checked the position of the needle before each experiment,
and for each one I had the needle in the same place. The needle had to be sitting just
on the surface, so it could break away from the liquid, and this was kept constant
throughout.
The height and place I dropped the rice grains from was another problem assessed in
my experiment. If the grain was dropped from too high above the cup it had to fall a
long way, therefore picking up speed and force. This simple mistake could affect the
results and so I decided to drop the grains from the same height each time, which
was just above the rim of the cup. Another issue with placing the rice grains in was
bumping the string or the cup that could cause movement of the balanced beam and
could wrongly influence the results. To prevent this I used tweezers to individually
place the grains in, as tweezers are thin and precise. This solution meant the grains
could be placed in more carefully with fewer mistakes.
When changing the temperature of the liquid I removed liquid from the glass added
hotter or colder water or oil using a syringe. While this method allowed for exact
measurements of water to be taken out and replaced it also had problems. One of
these problems was that the temperature was not evenly distributed throughout the
liquid. To solve this I stirred the liquid gently using a spoon to disperse the particles
and ensure a constant temperature. After stirring the surface was too disturbed to
place the needle back on it so I had to wait until it had stilled to begin measuring
again.
The final concern was in regards to the string holding the needle and the cup, which
presented problems due to length and sliding along the beam. A variable I identified
was that the two pieces of string were not equal. I thought this might be affecting
the accuracy and the tilting of the beam. As a solution to this I made the string
lengths equal, with both sides having lengths of 22cm. The other problem, which the
string presented, was that it slid on the beams. This could have caused accuracy and
measurement problems. To prevent this I checked that the string was on the end of
the beam before every experiment.
Further
To improve the overall accuracy of my experiment I needed to have a more scientific
apparatus. This could prevent the problems with balance, positioning and outside
factors affecting my results, which were collected from the homemade apparatus. A
more scientific apparatus could take exact measurements by controlling the
problems and providing standard procedures for each experiment.
In the future I would like to further investigate surface tension, however, discover
more comparisons. A future experiment could involve measuring the surface
tensions of various liquids e.g. milk, petrol, wax and salt, and comparing the results.
Conclusion
Through the results presented in my experiments I have been lead to conclude that
my first hypothesis is confirmed and that “If the surface tension is related to the
temperature of the liquid, then liquids at higher temperatures will have lower
surface tension, and liquids at a lower temperature will have a higher surface
tension. This is because the higher the temperature of the liquid the more the
molecules move around, thus breaking the surface tension. ”
However, my second hypothesis “If the surface tension of a liquid is related to the
liquid being measured then the surface tension of olive oil will be higher than that of
water. This is because oil has a higher viscosity than water” was disproved.
From the results I obtained I discovered that there is a clear relationship between
temperature and surface tension. I found that as temperature increases surface
tension decreases for any liquid. I also found out that on average, the surface
tension of water is lower than that of oil, through discovering that viscosity and
surface tension do not relate.
References
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Acknowledgements
o Mum (Amanda Snelling) – helped with counting rice grains, changing the
temperature of the liquid and experiment design.
o Dad (James Lonie) – helped with the construction of the apparatus and
parental supervision during this.
o Sister (Beth Lonie) – filmed me taking measurements and took photographs
of the experiment at various stages.
o Brother (Ben Lonie) – taught me how to write a discussion and proofread my
final report for mistakes.