My son is turning 10 next week and he is having a birthday party. I am wanting to put on some amazing science experiments dressed up as a “mad scientist”. What are some good experiments I could do to WOW a group of youngins? I am thinking of showing the effects of air pressure by boiling some water in a can and turning it over into a shallow pan of ice water to condense the water vapor inside and immediately crushing the can. What else can I do? No access to liquid nitrogen. Shame that. 
Head over to youtube and do a search on Julius Sumner Miller.
He hosted an Australian TV show devoted to science, on which he conducted numerous scientific experiments. The show was pitched at a children’s audience so will have quite a few experiments you can use I would think.
When my daughter was 11 my husband showed up with his friends from the university particle physics lab and demonstrated a Tesla coil. Now that will light up anybody of any age. Literally!
Watched an old episode of QI last night where they extinguished some candles by pouring invisible C02 over them
just need baking soda , vinegar and a candle
http://chemistry.about.com/od/funfireprojects/a/candle-science-magic-trick.htm appears to be the same thing
I did that experiment in front of 30 10 and 11 year olds, they were all amazed, and the theories they came up with for what was happening ranged from the accurate to truly bizarre.
The same class also loved investigating fingerprints, especially when they had to use their knowledge to solve a “crime” (finding out which teacher smashed the plate).
It really doesn’t take much to impress that age group.
If you can get some, I think sulphur hexafluoride is pretty impressive: http://www.youtube.com/watch?v=1PJTq2xQiQ0
Could you get together the chemicals for an iodine clock?
I run “Hsands-on Science” for kids of that age at our SF convention. My criteria are that you have to be able to explain it in the time of a TV commercial, they can do it with easily-available materials, and they can think of ways to keep coming up with their own experiments. And it can’t be dangerous. Here are some things I’ve done:
1.) Mentos in Diet Soda – always a winner.
2.) Inflation – put powder in a balloon attached to the neck of a bottle with liquid in it. The obvious thing is to use baking soda and vinegar (use a funnel to put baking soda into the uninflated ballon, put vinegar in the bottle. Attach the balloon to the bottle neck without letting the baking soda fall into the viegar. When you’re ready to go, just hold the balloon up straight and the baking soda falls into the vinegar, making carbpon dioxide and filling the balloon. You can make up other possibilities, like crushed Alka Seltzer/water, or salt/soda, and others. Will baking powder work? How about Pop Rocks and water? Crushed Mentos and soda? Denture cleanser and water?
3.) Black Light – get a GOOD Blacklight (easy now – Halloween stores atre selling them, as is Spencer’s) and fluorescent paints/crayons/paper. Show them the anti-counterfeting features on money (US money finally has them, although foreign is still better) and on credit cards and passports.
4.) Tin Can telephones. You can do paper cup and string telephones, too, but metal cans and wire are better
5.) Slime – look up recipes on the internet. Diluted White Glue (like Elmer’s) and Bprax solution works well, and is easy to get. You can send to somewhere like Spengler’s for polyvinyl alcohol, which mixed with borax solution gives you clear slime (or colored transparent slimre, if you color it). You can also make corn starch + water “oobleck”. Fun but messy.
6.) Fast chromatography. Use paper towels and washable magic markers. Chromatography timre is reduced to seconds.
7.) Build your own spectrscope. Using CDs or DVDs. A use for those rotten movies and free software that people send you.
8.) Strobe lights and stroboscopes. Again, Halloween stores are selling strobe lights now. Or you can make a strobe disc with a wheel of cardboard with slots cut in it mounted on a stick frely spinning.
There’s a scene from The King and I with Jodie Foster where she has a large clear glass jug, put a piece of burning paper down the mouth of the jug, waits a moment, and then sets a boiled egg (no shell) on top. As the air in the jug cools off after the combustion is over, the difference in air pressure forces the boiled egg into the jug, even though it appears at least half an inch wider than the mouth of the jug. Very cool science for the 19th century.
Oh, and one I did with sixth graders when I got to teach science - making a polymer out of borax and Elmer’s glue. You can add food coloring for fun. The less borax, the runnier the gel. The more borax, the firmer. It’s good to have sealable baggies on hand and warn the kids that the more they handle the gel, the sooner it’ll lose its cool properties.
If you’ve got some of those old film canisters (the fujifilm ones are the best, cause the lid stays on tight), you can use baking soda and vinegar to make rockets. Pour a bit of baking soda in the canister, pour in a bit of vinegar, snap the cap on, invert it, and get outta the way. They can fly pretty fast pretty far though, so that might be a concern.
Powering a flashlight bulb with a potato or a lemon is always good fun. Plus, you can eat the lemon when you’re done. Not too showy compared to some other stuff though.
There was a trick one of my science teachers did in high school where he took a little bit of alcohol (presumably isopropyl or something like that), poured it into the bottom of an empty water bottle (the big kind you see on water coolers), covered the opening and shook it around a bit to spread the alcohol around, and then he turned off the lights and dropped a lit match into the bottle. Due to the airflow involved (big wide bottle, narrow top) and the dispersal of the alcohol, the effect was a short-lived jet of blue flame that sorta curved up from the bottom of the bottle up the sides towards the top (the fire was sucking air in through the mouth of the bottle).
Of course, practice caution when using fire, particularly around impressionable and inexperienced little kids.
My daughter (9 going on 10) loved the Ivory Soap in the microwave trick
Schrodenger’s hamster?
Oh my goodness he was a real guy?! I thought he was just character on Hilarious House of Frightenstein!
My kids loved sucking a hard boiled egg into a bottle with a flame.
The fun part is challenging them how to get it out again without damaging the egg.
Invert the bottle. Blow *into *the bottle, and the increased air pressure will push the egg out.
Lots and lots of other fun experiments at this site.
Anything to do with dry ice is an automatic winner. At my son’s science fair, the fathers were about four deep around his exhibit.
The trouble is, although demos are cool, there has to be a curriculum-linked learning objective, otherwise you’re just entertaining the children and not educating them.
Ideally, you want things that they can do and fiddle with variables themselves.