Naked Science Forum

On the Lighter Side => Science Experiments => Topic started by: thedoc on 08/12/2013 12:30:02

Title: How do I make a bicarb-powered rocket?
Post by: thedoc on 08/12/2013 12:30:02

Safiyya asked the Naked Scientists:
   
My son is in grade 4 and has a project:
They have to make a rocket using a plastic bottle. I have tried vinegar and baking soda but I don't think my measurements are correct.

Could you please tell me how much I should be using to make it go up about 1 metre?

Thank you
Safiyya

What do you think?

Title: Re: How do I make a bicarb-powered rocket?
Post by: RD on 08/12/2013 13:53:11

Apparently half an Alka-seltzer tablet in a film*-container half full of water will go 1 meter ...

[ * if you can't find a film container maybe a similar sized medicine pill container will do ]

Title: Re: How do I make a bicarb-powered rocket?
Post by: CliffordK on 08/12/2013 18:31:04

You're dealing with weak acids and bases, and possible "explosions".  It never hurts to put on safety glasses or goggles.

The trick, at least in the video is to keep it sealed so that it builds up a little pressure (but not too much), then to release the pressure in a controlled fashion. 

Could you get a wine cork to loosely fit into a soda bottle?  Enough for a seal, not enough to require a cork screw.  A little wax or moisture might help the seal.  A screw top on a plastic bottle is probably bad as you wouldn't be able to control the explosion.

You probably don't need too much vinegar/soda.  A teaspoon or so of soda.  I could probably figure out the proportions.  But, since the soda is essentially concentrated, and the vinegar is dilute, I'd use somewhat more vinegar than you use soda.  It would be easy enough to do a simple experiment to see how much vinegar it takes to dissolve the soda (plus a bit extra, I think).  Do you have sealable plastic bags?  Put your water/vinegar mix into a sealed plastic bag without air.  Design the experiment to separate the two until the bag is sealed. Figure out which one gets biggest.  You can do that experiment with your kid too.

The design of the old soda fire extinguishers was to keep the soda/vinegar separate inside the fire extinguisher until it was inverted.  If done right, you could put the vinegar into the bottom of the bottle.  Use a paper towel or something full of soda tied up with a thread to your cork.  Once you get the seal you want, turn it over and let it go.  A stand of some sort would be helpful.

Title: Re: How do I make a bicarb-powered rocket?
Post by: distimpson on 09/12/2013 18:58:42

largest number of film container alka seltzer I've seen:

http://www.youtube.com/watch?v=1nX8jvj_jOk (http://www.youtube.com/watch?v=1nX8jvj_jOk)