24 September 2010

Kitchen experiments

Some simple, if possibly messy, fun.  Ingredients: Water and corn starch, baking powder and vinegar.

The baking powder and vinegar mix to release carbon dioxide gas.  If you put it inside something with a tight cap that can blow off, you've got a 'rocket'.  Just be sure to aim it away.  I don't really remember well, but I think equal vinegar and baking powder is the right recipe.  But it's something to experiment with.

Corn starch and water is a chance to explore the mechanical properties of matter.  (read: mess around while claiming to be doing science)  Ordinary fluids, like air or water, react straightforwardly to pushing on them.  If you push, they move out of the way.  Push harder, they move out of the way faster.  Corn starch and water (again, I think it's equal amounts, but experiment) are a different kind of thing.  Set a marble on top of the mixture and it will sink through.  Throw the marble at it, and it will bounce. !?  Experiment.  It makes a difference how fast you push.  Lots of room for experimentation.

Anyone else have comparably simple experiments?


Anonymous said...

There are a couple more things you can do with baking powder and vinegar: the easy one is to light and candle, and then pour the CO2 onto the candle to extinguish it.

The more complex one is to very carefully weigh the baking powder, weigh the vinegar, weigh the container, add them together, pour out the CO2, and then weigh the remainder... it turns out that you can pretty accurately predict the mass loss based on writing out the balanced chemical equation and doing some calculations. I actually had a high school chemistry class do this...

My other kitchen favorite is the red cabbage pH indicator: takes a little effort to extract the indicator from the cabbage, but once you have it, then you can have pH fun with anything and everything you want to test - soda, vinegar, baking soda, ammonia, etc....


warmcast said...

Some thoughts:

1. Put an egg in vinegar until the shell has dissolved. Sort of demos the potential of ocean acidity??

2. The bubbles produced by carbonated drinks is caused by the dirt on the glass. Not exactly an experiment!

Anonymous said...

One of my other favorite egg experiments is the "gas expands when hot" demo: take a beaker whose mouth is just a bit smaller than a shelled, hard-boiled egg. Drop a lit match into the beaker, wait a couple seconds, and then set the egg on top. The match will go out, and then, a little while later, "plop!", the egg gets sucked into the beaker as the air cools and contracts.


Horatio Algeranon said...

It's a bit embarrassing to admit it, but a chemist at Horatio's alma mater (Stanley Pons at U of Utah) purportedly used to do Cold (con)Fusion in a test tube in the kitchen there (late at night, when no one else was around).

Unfortunately, Horatio can't say just how he did it -- nor can anyone else for that matter (with the possible exception of Martin Fleischman, and he's not talking)

Others tried, of course (at MIT and other top notch Universities) but, if their failure is any indication, it may well be the most difficult experiment (kitchen or otherwise) of all time (time travel to the past might be easier ).

But don't let Horatio discourage you from trying...

Anonymous said...

Endothermic reactions are always fun, because they're a little counterintuitive: Haven't tested this myself, but lemon juice plus baking soda should work, which could be fun. (I've done the chemistry lab equivalents for "magic shows", but I think we used non-kitchen ingredients). Dissolving salts in water can sometimes work (I think KCl is better than NaCl for this purpose).

Also, making ice cream in a plastic baggies: eg, crushed ice and salt in the outer baggie, and the ingredients in the inside baggie, and a thermometer to show that the salt + ice mixture goes below zero degrees.

Finally, back in my chemical demonstration days, I really liked the Shakhashiri series of books:


Anonymous said...

Hey, he has a webpage:


Matt S said...

From the opening I was hoping to see something about cornstarch, water, baking soda, and vinegar all mixed together. Oh well.

Robert Grumbine said...

Could you describe how to extract the pH indicator from cabbage? Never heard of that before, though I know that the original pH indicators were plant-derived.

Matt S:
Hmm. Having gotten your hopes up, I'll contrive an experiment/demo for you now. In one bowl/cylinder, pour some baking powder. In another, mix up the cornstarch and water, after finding what produces a good mixture (stiff vs. throwing the marble at it). Then pour the mixture on top of the baking powder layer.

Now, lower, say, a turkey baster with of vinegar (having similarly experimented to see what the right proportions are), so that the nozzle is in your baking powder layer. Squirt out the vinegar and stand back. If the proportions are all correct, the CO2 released in the baking powder/vinegar will slap into the cornstarch layer rapidly, so the cornstarch will react as if it were stiff.

Never tried it myself. The cleanup process promises to be significant.

Anonymous said...

Hmm. I thought I posted this before, but: my favorite series of chemistry experiment books for use in chemistry demonstrations was the Shakhishiri books, and I found he has a webpage with a list of household experiments including the red cabbage pH indicator: