From: Hauser, Michael (MHauser@stlcc.edu)
Date: Wed Feb 26 2003 - 12:44:33 EST
I had the opportunity this week to use the nuts and bolts analogy to
illustrate strong and weak acids and bases. After a bit of time, the
students figured it out. The real bonus came shortly thereafter when I
started explaining the structural characteristics that make acids strong or
weak. I showed a long bolt with the nut barely on AND a similar sized bolt
where the nut was wound way down onto the bolt.When I asked which bolt could
more easily "dissociate" the nut, they all answered correctly. NOW I was
ready to discuss dissociation as it relates to the electronegativity, size,
etc of the "non H" atom. Acids that hold on tightly to their H are weak
acids.
A short while later we started pH. I used a measuring tape where I marked
off the log scale as shown on the video. I think I had been taking it for
granted that students understand what "logs" are besides a button they push
on the calculator.
It worked and I advise the use of one of the cloth measuring tapes that
winds up into a reel in a case. We marked the 1cm, 10 cm, 100cm and 1000 cm
areas with large paper clips as we unwound it. I was standing in the hallway
when we got to the 10 to the 3 power! Discussion of the Richter scale
difference between a "5" and a "6" really amazed them.
Michael Hauser
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