Chemical Purity

name         Steve
status       educator
grade        6-8
location     WI

Question -   I am trying to use chemicals to illustrate the 
idea of purity.  I was thinking of having 2 glasses, each 
containing a different clear liquid.  Then I wanted to drop 
another liquid into each glass with a reaction coloring the one, 
but not effecting the other.  Then what I was thinking is that 
the unaffected liquid might even be poured into the colored 
liquid and clear it up. Is this demonstration even possible with 
over the counter chemicals?  Are there liquids that would 
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You will have to adjust the concentrations, but a good combination 
is potassium permanganate which is a very purple solution (you can 
find this in hardware stores or building supply stores in the area 
for regeneration iron absorption water filters) and sodium sulfite 
or sodium thiosulfate (you can find in photographic chemical supply 
stores, either as separate supplies or as the major component of a 
blend called ''fixers''). Use two test solutions: sodium sulfite and 
permanganate. A couple of drops of water into each solution will not 
cause any change in color. However, if you mix the two stock 
solutions of permanganate and sulfite, and the sulfite is in excess 
the solutions will turn from a deep purple to a nearly colorless 
solution. If the concentrations are large enough there could be a 
faint pink solution due to Mn(+2) which is pink, but the change is dramatic.

Vince Calder
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