Tiny BUBBLES....

This is a cute little demo showing density and demonstrating one of my favorite addages,

I perform this demo with absolutely NO EXPLANATION 1st. In an empty aquarium or large visible sink, place a few cups of baking soda. Pour a cup or two of regular white distilled vinegar on top of the baking soda. (Actually, I use an entire 3 pound box of baking soda and half gallon of vinegar to get a HUGE amount of CO₂.) A chemical reaction is obviously taking place. Now comes the fun part. Blow a bunch of bubbles over the top of the aquarium or sink. Do not blow INTO the aquarium; this will stir up what's going on. Blow the bubbles over the top so they will settle down into the aquarium.

The kids are absolutely amazed that the bubbles that enter the aquarium stop falling and float in mid-air. Have them explain what's happening. [The baking soda and vinegar combine to produce CO₂, carbon dioxide, gas. CO₂ is denser than regular air so it stays inside the aquarium. Density of air is about 1.29 kg/m3 while CO₂ is almost 2 kg/m3. When the bubbles, just slightly more dense than air, slowly sink into the aquarium, they bump into the CO₂ layer. They will then become more buoyant and float.] Additionally, you can observe for a while longer to notice the bubbles will swell up and sink to the bottom. This is, I believe, due to CO₂ seeping thru the soap film wall making the bubble's composition more like that of CO₂'s and it will sink. Cool. What other job allows you to blow bubbles and get paid?

The exact chemical reaction? Well, since I'm a Fizzix guy, I taught the wrong equation for years. It was pointed out to me by my more than capable and extremely cute Johns Hopkins Lab Assistant in 1999, the real chemical equation is

Hi Daryl: I have been using your WalMart physics since the Philly meeting and I found something new this year. When I make the tubful of CO2, I lower candles or other flames into it to show how it extinguishes them. This year I was using a butane lighter and lowered it slower than usual. Suddenly the flame remained at the height of the CO2 while I lowered the lighter several additional centimetes, keeping the button pushed. The butane was rising through the CO2 but could not burn until it got above the level of the sides of the tub and there the flame continued burning happily as long as I kept sending butane up to it. I am going to try it with propane from a plumbers torch and natural gas from a bunsen burner next time I get the chance. Moving the lighter sideways is another idea I have not tried yet but will. I think I can get the flame to trace my motion in delay. I think you will like this one. By the way, I did not see the CO2 demo on your site this time. Did I miss it? Bruce Williamson Delaware Valley Friend's School, Paoli PA

1. Construct a 'V' ramp a few feet long. I use two 2x6' pine shelf planks attached perpendicularly. Pour the CO₂ out so it runs down a "V" ramp toward an unsuspecting lit candle at the bottom. The kids are absolutely amazed that an 'invisible' thing would cause the candle to just snuff out. This fits in nicely as a demo of the Camaroon tragedies mentioned at my Pepsi Demo page.
2. Another cute thing you can do is a little ditty from my hero, Bill Nye. Place two large paper bags either on a GOOD equal arm balance or make a lever arm scale from a meter and fulcrum and hang the bags from opposite ends of the stick to balance. Now, pour the CO₂ from the aquarium into one of the bags. The kids neat-o expressions are all you hear when the balance tips to the side where you poured the 'invisible' stuff. NEAT!