Christie W.
11/05/08
Measuring the Width of a
Molecule
A.
Purpose:
The
objective of this experiment is to demonstrate how to measure molecules using a
procedure entailing the use of both chemistry and algebraic concept.
In chemistry,
a molecule is defined as a sufficiently stable electrically
neutral group of at least two atoms
in a definite arrangement held together by very strong chemical bonds.
It can also be defined as a unit of two or more atoms held together by covalent bonds.[1][2]
Molecules are distinguished from polyatomic ions
in this strict sense. In organic
chemistry and biochemistry, the term molecule is used less strictly and also
is applied to charged organic molecules and biomolecules.
(Wikipedia)
The
size and shape of a molecule depend on the type and number of atoms that make
up the molecule and how they are arranged. The smallest molecules—such as
hydrogen, oxygen, and water molecules—contain only a few atoms. These molecules
are smaller than one-millionth of a meter at their widest point. Scientists
usually measure them in Angstroms (Å), where one Å is 10-10 (or
1/10,000,000,000) meters. The hydrogen molecule, made of two hydrogen atoms, is
about 1.5 Å. The oxygen molecule, made of two oxygen atoms, is slightly larger,
since oxygen atoms are slightly larger than hydrogen atoms are. (Encarta)
This
experiment hopes to show that, using relatively simple procedures, one can
measure the width of a molecule and see how truly small they are, and yet how
they are not completely unknowable. Through a series of mostly indirect
procedures, the experimenter will ideally gain a greater understanding of these
procedures, how scientists use them, and what great potential these methods and
operations posses in the world of scientific exploration.
Since
all of chemistry relies on a great understanding of atoms and molecules, the
ability to find how large (or comparatively small) atoms and molecules are is
of great importance to both individual scientists and the entire foundation on
which modern chemistry relies.
Hypothesis:
If the calculations involving the mole concept, molecular mass, and algebraic
principles are carefully made by the experimenter, then the number representing
the width of a sodium stearate will be between n x 10-8 and n
x 10-7.
B. Equipment:
1. Safety goggles
2. Eyedropper
3. Stirring rod (or spoon)
4. Water
5. Large glass (at least 16 ounces)
6. Dishwashing liquid
7. Large bowl
8. Pepper
9. Ruler
C. Procedure:
1. Fill large bowl almost completely full of
water, leaving only an inch or so of space from the top of the bowl.
2. Quantitatively measure 5.0 mL of dishwashing
liquid into graduated cylinder.
3. Along with the dishwashing liquid, fill
cylinder up to 50.0 mL with water.
4. Pour contents of cylinder into large glass.
5. Fill cylinder again up to 50.0 mL mark.
6. Repeat this step six more times, so that
395.0 mL of water and 5.0 mL of soap reside in the large glass.
7. Stir contents of glass slowly.
8. Calibrate eyedropper. Clean and dry graduated
cylinder and use eyedropper to transfer 10.0 mL of diluted dishsoap from glass
into cylinder drop by drop. Count how many drops it takes to reach this mark.
9. Take the number 10.0 and divide it by number
of drops counted. This is how many mL each drop contains.
10. Sprinkle pepper onto surface of water in
large bowl.
11. Use eyedropper and put one drop of diluted
dishwashing soap into center of peppered water.
12. Quickly measure the diameter of circle formed
by the soap pushing the pepper back.
13. Take the volume of one drop from eyedropper
and multiply it by density of dishwashing liquid (dilute) which is 1.00
grams/mL.
14. Multiply result by 0.000125 as this is the
amount of sodium stearate (roughly) which existed in the drop of dish soap.
15. Calculate molecular mass of NaC18H25O2
(sodium stearate.)
16. Use molecular mass to convert to moles.
17. Multiply result by 6.02 x 1023.
This answer is the number of molecules in sample.
18. Find area of circle formed by drop of dish
soap algebraically.
19. Divide this number by number of molecules
found in sample.
20. Take square root of this number to find width
of the molecule.
21. Clean up the mess.
D. Observations:
1. The experimenter decides to use Dawn ®
dishwashing liquid for this experiment as is explicitly states on the label
that it is not intended for use in dishwashers.
2. The experimenter tends to have a problem with
second-guessing herself as to how many times she has placed 50.0 mL into the
large glass, so she checks herself by measuring and making sure that two cups
of liquid reside in the large glass.
3. The experimenter tires of putting so many
drops into the glass, so she fills the cylinder to 5.0 mL and doubles the amount
of drops to find the amount of drops it would have taken to fill it to 10.0 mL,
which happens to be 220 drops per 10.0 mL of solution.
4. Using procedure above, the experimenter
calculates that each drop from the dropper contains .045 mL of solution.
5. When the drop is placed in the center of the
bowl, it clears out a large circle in a very small amount of time so as to
catch the experimenter off guard and without the ruler in place. Regardless,
with two other tests she determines that the diameter of this circle formed is
20.2 cm.
6. When (.045 x 1.00 g/mL) is multiplied by
0.000125, it amounts to 5.63 x 10-6.
7. Molar mass of NaC18H25O2
is 296.3 g per mole.
8. (5.63 x 10-6) / (296.3g/mol) =
1.90 x 10-8 moles of NaC18H25O2
9. 1.90 x 10-8 x 6.02 x 1023
= 1.14 x 1016 moles of NaC18H25O2 in
sample.
10. 20.2/2 = radius of circle = 10.1 cm. πr2
= 320 cm2.
11. Area occupied by each molecule = 2.81 x 10 -14
cm2.
12. Square root of 2.81 x 10 -14 cm2
= 1.68 x 10-7 cm = width of a NaC18H25O2
molecule.
E. Conclusions:
The
hypothesis stated above was supported by data gathered by the experimenter;
when the calculations involving the mole concept, molecular mass, and algebraic
principles were carefully made by the experimenter, the number representing the
width of a sodium stearate was indeed between n x 10-8 and n
x 10-7, amounting to 1.68 x 10-7 cm.
In
this experiment the experimenter filled a large bowl up with water and
sprinkled pepper on top so as to facilitate and demonstrate the effect of the drop
of dilute dishwashing liquid on the surface of the water. The experimenter
diluted 5.0 mL of dish soap to 400.0 mL with water. One drop (consisting of
.045 mL) of dishwashing soap was carefully placed in the center of the
peppered, water-filled bowl. The diameter of the circle made by this drop was
measured to be 20.2 cm. Then, after finding the proportionate amount of sodium
stearate existent within this circle, the experimenter used molecular mass and
the mole concept to find how many molecules of sodium stearate occupied this
amount of space. Then the experimenter divided the area of said circle (derived
algebraically) by the number of molecules existent within it to find how much
area each molecule occupied. Taking the square root of this area, the experimenter
concluded that the width of a NaC18H25O2
molecule, according to data, must be approximately 1.68 x 10-7.
This
experiment could have been improved by, rather than re-testing it, readying the
ruler over the bowl before the drop of soap is placed in it so as to record the
size of the circle formed at its very largest.
Ideas
for further research were generated by the fact that, during the experiment, a
dilution of the soap was required. The experimenter hypothesizes that this
might be because either the circle formed by a single drop would be too large
for the bowl and therefore would not form a single layer of NaC18H25O2
molecules, or that, had a larger bowl been acquired, the numbers that the
experimenter would have to work with would be too large to easily use.
F. Bibliography:
"Molecule,"
Microsoft® Encarta® Online Encyclopedia 2008
http://encarta.msn.com © 1997-2008 Microsoft Corporation. All Rights Reserved.
Domain: http://encarta.msn.com
Document: /encyclopedia_761563983/Molecule.html
Rosenoff.
Steve. Class Lecture. November 5, 2008
Wikipedia Contributors,
"Molecule," Wikipedia, The Free Encyclopedia
Domain: http://en.wikipedia.org
Document: /wiki/Molecule
Wile, Dr. Jay L. Exploring Creation with Chemistry, 2nd ed. CJK: Apologia Educational Ministries, 2007.