capillary action and nonpolar substances

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From: Geoff Ruth (gruth@leadershiphigh.org)
Date: Mon Jan 28 2002 - 19:01:19 PST 

Message-Id: <a05010401b87bbd37823a@[192.168.1.172]>
Date: Mon, 28 Jan 2002 19:01:19 -0800
From: Geoff Ruth <gruth@leadershiphigh.org>
Subject: capillary action and nonpolar substances

Hi!

I am confused by an experiment I did in my chemistry classes today.
We were looking at intermolecular properties. I had students test
various liquids to see how much capillary rise they showed. To my
horror, nonpolar substances like cyclohexane and oleic acid (aka
olive oil) rose just as high as hydrogen-bonding substances like
ethanol and water. This makes very little sense to me: my thinking is
that nonpolar substances should have little or no adhesion to the
polar SiO2 (with H's attached to some ending O's) glass walls.
Therefore, they should have no capillary action, to my thinking.

I've tried to research this on the web, but the only slightly helpful
thing I've found is this:

Capillary action occurs when adhesive forces exceed cohesive forces.
The liquid creeps up the tube until a balance is reached between
adhesive forces and the weight of the liquid.

I can't really apply this idea to explain why both very polar
substances and very nonpolar substances would show capillary action.
I need help!

- Geoff

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