Intermolecular forces
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Why does the meniscus in non-polar hydrocarbons form a 'u'-shape? As hydrogen bonding is not involved with bonding to the glass (as in water) this should not occur. Why isn't it 'n'-shaped or a flat?
A response from Ulex
My first reaction to this question is to question the premiss. Whilst the meniscus of a liquid hydrocarbon in a glass tube is certainly not ‘n’ shaped, I don’t think it is ‘u’ shaped either.
I could be wrong about this and do not have access to a laboratory to check. So I am taking this opportunity to throw this very interesting question open to teachers generally – I really would like to know the answer myself.
You will find a helpful discussion of the shape of a mensicus at the web site of the Chemistry Department of Purdue University. Click on 'surface tension' in the table at the top of the page.
It looks like the shape of any meniscus results from the balance of the adhesion to the walls versus the surface tension. Even with a hydrocarbon there will be some surface tension because of the van der Waals forces and so there must be some interaction with the walls.
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updated: 25 August 2003
