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Any ideas for EYH presentation (fwd)

Barb Lewis barb at nmrfam.wisc.edu
Thu Feb 2 17:11:42 EST 1995


In article <Pine.SOL.3.91.950201172422.19614H-100000 at dale>,
mymcnair at UCDAVIS.EDU (Michelle McNair) wrote:
 (snip)
 
> Something I really remember one of my undergraduate professors doing was 
> a quick chemistry presentation that involved a lot of color changes - you 
> know, phenylthaline (sp) in a clear acid going bright pink when more 
> clear acid 
> was added, or copper changing color with oxidation states, etc.  I wish I 
> could get in touch with the prof. that did it, because I work with 5th 
> graders as a science mentor & am too lazy (and a genetics grad student 
> that avoids chemistry - I know, it's a lame excuse) to figure it out for 
> myself.  
> 

One easy and completely safe way to get color changes is the following (I
got the idea from U. Wisc. Chem dept's Institute for Chemical Education):

Take a wedge of purple ("red") cabbage; homogenize it in a blender with
water.
(More cabbage/less water gives more concentrated juice, which can then be
diluted. The amounts really don't matter except for intensity of color.)

Filter the result through a sieve or, better, cheesecloth.

This juice will probably be purple (if water pH is pretty neutral). Adding
acids (safe ones include lemon juice, vinegar) turns it pink. Adding a base
turns it a nice blue (e.g., baking soda; not sure what else is easy and
safe (Drano or lye is easy, but not too safe!))

Adding baking soda after vinegar or lemon juice, or vice versa, gives nice,
messy (but still safe) bubbling...

(This is a pretty short experiment - not enough for a whole session. More
spectacular are the oscillating reactions which keep going back and forth;
I can search further for info on these if anyone wants.)

Barb Lewis
e-mail: barb at nmrfam.wisc.edu - My own opinions, of course



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