Title: Measuring the Size of an Oil Molecule
Subject: Science
Grades: 9 – 12
Category: Nanotechnology
Lesson Overview:
In this activity, students estimate the size of an oil molecule. The student places a
drop of oil on water and then spreads the oil across the water. By estimating the
area covered by the drop of oil, the student can calculate the size of an oil molecule.
The activity shows that nanoscale objects (such as an oil molecule) are discernable
and quantifiable using relatively simple methods.
Learning Objectives:
Students will be able to:
• Measure the size of an oil molecule
• Describe procedures for measuring nano-sized particles
• Explain the importance of nanotechnology
Academic Standards:
National Standards (Grades 5–8 and 9–12)
• Science And Technology. Content Standard E: Understandings About Science
And Technology
• Science And Technology. Content Standard E: Abilities of technological
design
Time Frame:
This lesson requires one 45-minute session to complete. (Optional preparation time
will require about half an hour and a wait overnight.)
Background for the Teacher:
We usually ask students to think big. In this activity ask them to think small.
Students often find it hard to relate invisible things to their everyday lives. Ask them
how to estimate the size of an oil molecule and they’d be hard-pressed to answer. As
everyone knows “oil and water don’t mix.” This activity uses that principle to
estimate the size of an oil molecule. The aim is to help students grasp the scale of
nanosize objects and also to discover that such objects can be discerned and
measured at scales we can perceive. Even though molecules are very small we can
learn about their structure using everyday materials. Nanotechnology is used in a
wide variety of applications including medicine, waste disposal and remediation,
energy production and efficiency, electronics, manufacturing and consumer goods.
It is already impacting our lives through commercially available products. The
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Communications, LLC.
science and technology is rapidly evolving, and people with a background in and
understanding of nanotechnology will be in great demand in the coming years.
Vocabulary*
Nanotechnology – a branch of engineering on molecular scales, typically less than
100 nanometers.
*First occurrences of vocabulary items are highlighted in the text.
Classroom Activities:
Materials for the teacher:
• Variety of household products created using nanotechnology:
o Titanium dioxide sunscreen (non-whitening)
o Microfiber cloth, stain repellent and wrinkle-resistant
o Color restore shampoo
o Anti-fog coating (available from auto parts stores)
o Glass protectant (various uses)
Materials for each group of students:
• Large shallow dish (exact size is not important)
• Small dish or tray
• Distilled water
• Talcum powder or other fine non-soluble powder (about teaspoon)
• Vegetable oil (about a teaspoon, olive oil works well)
• Ruler, metric, graduated in 0.5 mm increments or smaller
• Calculator
• Hand lens
• Card (about the size of a business card)
• Tape
• Fine stainless steel or copper wire
• Paper towel
• Two levelers, about the size of a ruler (straight metal rods or beams long
enough to span the width of the tray OR if optional preparation is followed:
two pieces of wood long enough to span the width of the tray)
• Micrometer (optional)
• Small wooden wedges (optional)
• Melting wax, about half a pound (optional)
• Hot plate (optional)
• Small saucepan (optional)
Safety note: The fine powder may cause allergic reaction (if using lycopodium
powder, for example). Allergy-prone students should wear a surgical mask. If the
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Communications, LLC.
optional preparation procedure is followed, students will be handling hot wax. They
should wear lab coats, safety glasses, and insulated gloves (such as an oven glove).
Engage
1. Show students a picture of the Deep Horizon oil well blowout. Describe how
one of the keys to limiting the impact of the oil spill was to understand how
oil interacts with water.
2. One approach to dealing with the spill was to use detergents that broke up oil
particles. Some methods and chemicals were more effective than others. How
can scientists predict and model the behavior of such chemicals? The answer
is through nanotechnology, the engineering science that concerns objects of
less than 100 nanometers. The term is usually applied to developing
technology that manipulates individual atoms and molecules.
Nanotechnology can help us understand how chemicals, water and oil
interact on a molecular scale.
3. What is a nanoscale object? Pluck a hair from your head (or show a picture of
hair). Explain that a human hair averages about one tenth of a millimeter, or
a little less than the thickness of a dollar bill. So how small is 100 nanometers
in comparison? To review units and exponents, explain the calculation if time
allows.
Step 1: Convert to meters
100 nm = 10-7 m
0.1 mm = 10-4 m
Step 2: Subtract the exponents: 7-4 = 3, therefore the difference is
10-3 m, and 10-3 = 1/1,000 = a thousandth.
Therefore a hundred nanometers is a thousandth of the diameter of a human
hair.
4. Nanotechnology is already impacting our lives through commercially
available products. Introduce the selection of products to the students. Ask
them which of the products involve nanotechnology. Of course it is all of
them. Therefore nanotechnology is already impacting our lives.
5. But how do scientists and engineers study and manipulate objects that are so
small? In this activity, students will learn that it is sometimes easier than
they might think. They will use a few everyday objects to measure the size of
an individual oil molecule.
Explore
A. GENERAL PRINCIPLE
Students prepare a flat container of water and use a dropper to add a drop of oil.
The oil is carefully spread across the water surface. The size of the molecule is the
volume of the drop divided by the area of the oil covering the water. Since the area
is very large and the volume is small, students will come up with a very small
number, of the order 10-7 mm. This is about the diameter of an oil molecule. The
accuracy of the results will depend on the care and precision students take in
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Communications, LLC.
performing the experiment. The optional preparation will require additional time
and overnight wait. If not using the optional preparation skip to Procedure C.
B. OPTIONAL PREPARATION
1. Melt the wax in the saucepan.
2. When it has entirely melted, run hot water over the tray and dry thoroughly.
3. Carefully pour the wax into the still warm tray, and spread evenly across the
bottom and sides.
4. If using the wooden levelers, dip one of the long edges into the wax. Repeat
for the second piece of wood.
5. Ensure the wax is evenly distributed across the bottom and sides of the tray.
6. Allow to cool overnight.
C. TO MEASURE THE MOLECULE
I. Prepare the tray of water.
1. Pour the distilled water into the tray until it is brimming over.
2. Use the small wooden wedges underneath the tray to ensure it is level.
3. Place the levelers in the middle of the tray (waxed side down if using the
wooden levelers) touching the water surface. Slowly move the levelers
towards the ends of the tray, until they are about an inch from the ends.
4. Very gently sprinkle the powder onto the water surface. Cover the entire
surface between the levelers, with a very fine coat of powder. If the powder is
too thick, the oil will not spread properly.
II. Prepare the oil droplet
1. Make a V-shape from the fine wire.
2. Tape the two ends of the V to the car so that a portion of the wire remains
protruding from the side of the card.
3. Add the oil to the small dish or tray.
4. Dip only the very tip of the wire V into the oil.
III. Make the measurements
1. Hold the oil droplet up to the ruler and estimate the diameter of the oil drop.
It should be exactly 0.5 mm, as measured with the micrometer (if available).
If the droplet is bigger than 0.5 mm it will spread too wide when added to the
water. If the droplet is bigger than 0.5 mm, make it smaller by using a second
piece of wire to pull away small amounts oil. If the droplet is smaller than 0.5
mm, record the diameter.
2. When the droplet size is 0.5 mm or less, gently touch the end of the wire V to
the water. The droplet will spread out on the water.
3. Students then measure the maximum diameter (D) of the oil spread out on
the water.
D. CALCULATE THE SIZE OF THE OIL MOLECULE
General principle: Due to the hydrophobic property of oil molecules a
monomolecular patch of oil forms as the drop spreads across the water. Therefore
the patch of oil is only a molecule thick and the thickness of the oil layer equals the
Copyright © 2011 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery
Communications, LLC.
size of a molecule. To work out the thickness we need two values, the volume of the
drop and the area of the spread out drop.
1. Calculate volume of the oil drop: Assume that the drop is spherical in shape.
The volume of a sphere is:
V=
4 3
πr
3
2. Calculate area of the spread oil drop: To calculate the area of the oil spread
out on the water assume the oil is spread out in an approximate circle shape,
so using D, the area equals:
A = π (D /2) 2
3. Calculate thickness of the oil layer: Since we know the volume of the oil drop,
we can work out the oil layer thickness from the formula for the volume of a
cylinder:
V = πr 2 h
where height (h) equals the thickness of the oil layer. Therefore,
h=
V
A
Therefore the size of an oil molecule:
oil patch thickness =
oil drop volume
oil patch area
4. To simplify the calculation, use SI units. For example:
Measured oil drop diameter = 0.5 mm = 5 × 10-4 m
Therefore oil drop volume:
3
4  5 ×10−4 
−11 3
V = π
 = 6.5 ×10 m
3  2 
Measured oil patch diameter = 220 mm = 2.2 x 10-4 m
Therefore oil patch area:
 2.2 ×10−1 2
−2
2
A = π
 = 3.8 ×10 m
2


And:
6.5 ×10−11 m 3
oil patch thickness =
= 1.7 ×10−9 m
−2
2
3.8 ×10 m
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Communications, LLC.
Since oil patch thickness approximates the length of the oil molecule, the size
of the oil molecule = 1.7 × 10-9 m = 1.7 nm.
Explain
1. In this way, we can estimate the size of an oil molecule using every day items.
Nanosized objects are accessible with a little ingenuity and several
assumptions.
2. Review the assumptions:
3. The oil molecule spreads across the water until it forms a monomolecular
layer only a molecule thick.
4. The oil drop is spherical.
5. The oil patch is circular.
6. Unimolecular composition of the oil. For example, although triacylglycerols
make up most of the volume of olive oil, other molecules include fatty acids,
glycerol, phosphatides, and sterols, among others.
7. Despite the assumptions, the example above demonstrates that this method
yields a result that is consistent with expectations. An oil molecule is
typically 2 nm.
Extend
1. Compare the result with other nanosize objects. For example, 1.7 nm is about
a fifth of the typical cell membrane thickness, or a little less than the
diameter of the DNA helix.
2. The experiment can be repeated using different types of oils, example
comparing mineral oil with vegetable oil.
3. Depending on the oil used, students can even estimate the size of an atom.
For example, oleic acid, which is found in many animal and vegetable fats,
has 18 carbon atoms in its fatty acid chain (C18H34O2). Therefore, using the
result above the size of a carbon atom is 1.7/18 = 0.09 nm, in close
agreement with the known size of a carbon atom, 0.07 nm.
4. For a lively discussion have students consider risks of nanotechnology.
Although much of the nanoscale physics is well-understood, considerable
uncertainty surrounds deployment of certain nanotechnologies. For example,
Chinese researchers found that a type of nanoparticle used in medicine can
trigger programmed cell death and if inhaled can cause lung damage. Other
concerns include long-term environmental impact and development of new
weapons of mass destruction. A debate format would work well for this topic.
Evaluate
1. A molecule of motor oil is about two times the diameter of an oleic acid
molecule. If you use a drop of motor oil the same size as the one for olive oil.
How would the size of the motor oil patch compare?
2. Describe two possible ways to improve the accuracy of your result.
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Communications, LLC.
3. If the average human height is 200 centimeters, and the distance from Los
Angeles to New York is 4,000 kilometers, what would be the distance from
Los Angeles to New York if a human was shrunk to 100 nanometers?
Scoring key for evaluation
1. Since its molecule is twice the size, the motor oil drop will have about half the
number of molecules as the olive oil drop if the volume of the drop is the
same. Therefore the patch will be half the size.
2. Possible answers: A more precise measurement of the volume of the drop. A
more precise measurement of the area of the oil patch. Use a purified
unimolecular oil.
3. To solve this problem, first convert all units to SI units:
a. Los Angeles to New York distance = 4,000 km = 4 × 106 m
b. Average human height = 200 cm = 2 m
c. Shrunk human = 100 nm = 1 × 10-7 m
Let scaled distance = x. Therefore, 2 m/4 × 106 m = 1 × 10-7 m/x. Solving for x
= 1 × 10-7 m/(2 m/4 × 106 m) = 0.2 meters. Therefore if a human was scaled
to nanosize height, the distance from Los Angeles to New York would be 20
centimeters, a little over the length of a dollar bill.
Self-evaluation
1. Have students assess their ability to carry out the procedure to get a realistic
estimate of the size of an oil molecule. How close was their result to the
expected result?
2. How could they have improved on the procedure?
Web resources
The Size of a Molecule (PDF), University of Central Arkansas, Department of Physics
and Astronomy
http://web.me.com/njaustin/PHYS1400/Laboratory/molecule.pdf
Estimating the size of a molecule using an oil film
http://www.practicalphysics.org/go/Experiment_633.html
Measuring the Diameter of a Molecule (alternative method)
http://www.worsleyschool.net/science/files/molecular/thickness.html
Health Risks Of Nanotechnology: How Nanoparticles Can Cause Lung Damage, and
How The Damage Can Be Blocked
http://www.sciencedaily.com/releases/2009/06/090610192431.htm
Could we use nanotechnology in medicine?
http://curiosity.discovery.com/question/nanotechnology-medicine
Copyright © 2011 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery
Communications, LLC.
What are some natural objects that people use in nanotechnology?
http://curiosity.discovery.com/question/some-natural-objects-in-nanotechnology
How could nanotechnology have an impact on the medical industry?
http://curiosity.discovery.com/question/nanotechnology-change-medicine
How is nanotechnology being used in cancer research?
http://curiosity.discovery.com/question/how-nanotechnology-used-cancerresearch
Why is the nanoscale important?
http://curiosity.discovery.com/question/why-is-the-nanoscale-important
Are there such things as organic nanotechnologies?
http://curiosity.discovery.com/question/are-there-organic-nanotechnologies
Further reading
Avison, J. (1989) The World of Physics. (2nd Edition.) Nelson Thorne.
Franklin and the Future: From Franklin's Oil-Drop Experiment to Self-Assembled
Monolayer Structures (PDF)
http://www2.avs.org/benjaminfranklin/richmond.pdf
Copyright © 2011 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery
Communications, LLC.
STUDENT TAKEAWAY – Measuring the Size of an Oil Molecule
Nanotechnology – a branch of engineering on molecular scales, typically less than
100 nanometers.
What is nanotechnology?
Nanotechnology is a technical and scientific field that concerns the engineering and
manipulation of objects less than 100 nm, or 100 billionths of a meter.
How are very small things measured?
It seems daunting to consider how to measure things that are so small that they
cannot be resolved even by powerful microscopes. However, there are numerous
ways to measure small things. An easy way to estimate the size of an oil molecule is
to measure the area of a drop of oil of known volume as it spreads across a water
surface. By assuming that a drop of oil spreads to a monolayer one molecule thick,
the size of a molecule can be calculated from measuring the volume of the oil drop
and the area across which it spreads on the surface of water. Although this method
makes several assumptions, it can provide a result in close agreement with
expectations.
What are the main applications of nanotechnology?
Nanotechnology is in the middle of burgeoning applications, likened by some to a
new industrial revolution. Nanotechnology has impacted many aspects of our lives
including domestic and household products, medicine, electronic goods, chemical
engineering, heavy industry and agriculture.
Why is nanotechnology important?
Nanotechnology is transforming our daily lives. Undoubtedly the existing and
potential benefits of technology promise improvement to numerous facets of our
lives. But nanotechnology may also carry risks that have yet to be fully evaluated. By
understanding the basic principles and facts of nanotechnology we are better
equipped to objectively consider claims of benefits or risks. For those considering
technical or scientific careers, nanotechnology offers numerous opportunities.
Essential Equations:
4 3
πr
3
Volume of a sphere
V=
Volume of a cylinder
V = πr 2 h
Area of a circle
A = π (D /2) 2
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Communications, LLC.
Thickness of oil patch
h=
V
A
= oil patch thickness =
oil drop volume
oil patch area
Web resources
The Size of a Molecule (PDF), University of Central Arkansas, Department of Physics
and Astronomy
http://web.me.com/njaustin/PHYS1400/Laboratory/molecule.pdf
Estimating the size of a molecule using an oil film
http://www.practicalphysics.org/go/Experiment_633.html
Measuring the Diameter of a Molecule (alternative method)
http://www.worsleyschool.net/science/files/molecular/thickness.html
Health Risks Of Nanotechnology: How Nanoparticles Can Cause Lung Damage, and
How The Damage Can Be Blocked
http://www.sciencedaily.com/releases/2009/06/090610192431.htm
Could we use nanotechnology in medicine?
http://curiosity.discovery.com/question/nanotechnology-medicine
What are some natural objects that people use in nanotechnology?
http://curiosity.discovery.com/question/some-natural-objects-in-nanotechnology
How could nanotechnology have an impact on the medical industry?
http://curiosity.discovery.com/question/nanotechnology-change-medicine
How is nanotechnology being used in cancer research?
http://curiosity.discovery.com/question/how-nanotechnology-used-cancerresearch
Why is the nanoscale important?
http://curiosity.discovery.com/question/why-is-the-nanoscale-important
Are there such things as organic nanotechnologies?
http://curiosity.discovery.com/question/are-there-organic-nanotechnologies
Copyright © 2011 Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery
Communications, LLC.