Measuring the size of a molecule

[ecy5maa]

Hi,

Homework Statement

I am trying to determine the size of a molecule..by doing the oil drop experiment where we drop a tiny droplet of oil on water covered with a thin layer of powder...and then make calculations based on the diameter of the circle... the droplet forms in oil.

The Attempt at a Solution

However, the oil droplet for me is not making a circle..rather is spreading out irregularly. How can I fix this.

Everything i have used is according to this site:

[PLAIN]http://www.practicalphysics.org/go/Experiment_633.html[/PLAIN]

but i have used talcum powder instead of lycopodeum powder

 

[Delphi51]

I never saw a circular oil patch when my students did this experiment.
An irregular size is not much of a problem because the whole experiment is more of an estimate than a measurement. Just estimate the area of the oil patch. You can make a very good estimate if you make a grid of square cm on a transparency and hold it over the patch. A nice touch is to estimate the minimum and maximum possible area. Use a number midway between these as your "best" value, but also work out the size of a molecule using the low and the high. Then you will have not only a "best" answer but a known accuracy range.