Dear daisy001,
Oleic acid is a substance with one hydrophobic and one hydrophilic
end. When a small amount of oleic acid is placed on the surface of
water, it stands on end with the hydrophilic end towards the water and
the hydrophobic end away.
oleic acid hydrophilic one end is the main point to solve this problem.
we will find the length of one oleic acid molecule by spreading a
small amount over the surface of water and measuring the diameter of
the circle. The oleic acid spreads itself into a one-molecule thick
layer in the shape of a VERY flat cylinder.
First, you must figure out the volume of a drop of water (or watertype
liquid). You may need some calibrated pipettes (plastic droppers with
0.25, 0.5, 0.75, and 1 mL markings). When the level of liquid is at
the line at the base of the bulb, there is 1.0 mL of liquid. Be sure
that there are no air bubbles. A good way to fill it exactly is to
fill it slightly less than 1 mL and then let a couple of air bubbles
out and liquid replace it. Repeat this until filled exactly to 1.0 mL.
Second, counting how many drops it takes to completely expel the
liquid. Be careful at the end that some apparent bubbles will be
mostly air. These can count as a half-drop. Repeat this procedure for
four times and record the results.
The following data should be included:
drops needed:
1st time:2nd time:3rd time:4th time
Circle Diameter:
1st time:2nd time:3rd time:4th time
then, you can know the volume of a drop of liquid.
Third, prepare a pan of water with insoluble natural powder(eg. powder
lycopodium or zinc stearate powder) and wait for it to calm down. This
step must be done with still water.
Finally, carefully put a drop of oleic acid in the center of the water
surface in your pan.
The oleic acid will push the powder out of the way forming a circle.
Measure the diameter of the circle in three different places and
record the result.
The circle formed is one-molecule thick.
So, The equation for the volume of a cylinder is V=h x pi x r^2.
Solve this equation for h.
As you provided, this is a 1 to 10 hotdog shape molecule.
h is 10x while the while w is x
the volume of one oleic acid molecule is 4/3 x pi x (x/2)^3 x h
note: oleic acid may disolve in solvents before the experiment, you
need to calculate the actual volume.
abbychau |
