From: SFPhysics@aol.com
Date: Wed Apr 09 2003 - 03:56:19 PDT
From: SFPhysics@aol.com Message-ID: <183.192dc1c2.2bc55653@aol.com> Date: Wed, 9 Apr 2003 06:56:19 EDT Subject: How Soap Works and Bar Practices...
<< Al, are you sure that the combination of water and a surfactant is a
chemical one? It sounds more like a physical change. If it is not a
chemical reaction then is the process just aided as the viscosity
decreases due to heat? And why then are barbacks instructed to rinse
their glasses in cold water?
Just wondering,
Kevin Kinsella
5th/6th Science Explorer
Woodside Elementary School
>>
Kevin, as I understand it, a detergent such as alkylbenzene sulfonate first
releases a cation upon dissolving in water. The resulting anion molecule
binds its hydrophobic hydrocarbonic end with an oil or grease molecule. The
leftover exposed hydrophilic end then attaches to a water molecule. When
enough detergent molecules coat the oil or grease droplet it lets go from the
fabric and goes into solution in what is called a micelle. The ionic bond
between the water and the micelle is what makes cleaning up detergent from
waste water a problem for water treatment plants of older designs. Even the
newest plants have to resort to detergent eating organisms to process out the
detergents and they are not near 100% effective. If the detergent only
performed some kind of physical change then removing it could be done by a
physical process like a flocculant not involving biochemistry. Remember, I
am not a chemistry teacher so my idea of what constitutes a chemical reaction
may not be true to a precise definition. Perhaps all the ionic action from a
detergent molecule is just a physical thing occurring in an aqueous solution.
Any Chemistry teachers out there want to clarify my thoughts for me? Do we
really need a new substance to qualify something as having undergone a
chemical reaction?
As for why glasses are rinsed in cold water in bars, have you ever had a shot
of whisky from a warm glass? The colder the libation the lower the alcohol
vapor pressure above the glass and the easier it is to down the shot. Think
about sake that is only a rice wine but when served warm it seems to have a
real kick to it. As for beer mugs, cold beer going into a warm glass will
foam much more. IMHO, the cold glass for non-carbonated beverages is for
aesthetics and faster sales. ;-)
Al Sefl
Who would more likely be seen at a sewage plant than at a bar...
And whose ideas usually don't hold water...
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