[shadow1990]

I'm looking for a demonstration that shows the properties of acids and bases; one that will amaze highschool chemistry students.  Anything that's fun to look at.  I have almost unlimited resources, (everything that can be found in a well-equipped highschool lab) so there's a lot to choose from.
I would have chosen a demonstration of what happens to a smal bit of Na or K when put in water... but my class has already seen that.

(if this should be put in the highschool forum, just tell me... I wasn't too sure where to put it)

[hmx9123]

A fun one that is easy for you is to put universal indicator solution in a large (like 1-2L) graduated cylinder and drop a piece of dry ice in it.  As the carbonic acid slowly forms from the CO2, you'll watch the color of the indicator change through the whole range.

[constant thinker]

This isn't necessarily acid/base, but I like it a lot and it involves an acid. Place a few drops of concentrated sulfuric acid into sugar. There is a highly exothermic dehydration reaction that occurs. Caution though concentrated sulfuric acid is dangerous and painful. I'd do this in a well ventilated area.

The "Chemical demonstrations" topic in the chemical education board may be useful to you.
http://www.chemicalforums.com/index.php?topic=16244.0

[hmx9123]

The dehydration of sugar with sulfuric acid smells mighty bad--so take constant thinker's advice and do it in a fume hood or outdoors.