Alka Seltzer Rocket!

Curriculum links:

• Physics and Chemistry – changes between solids, liquids and gases

Learning objectives:

1. Investigate how tablets dissolve and turn into a gas.
2. Investigate how air pressure builds up in a sealed container

Materials:

• Water
• Film canisters (old 35mm ones)
• Alka seltzer tablets
• Tub/Basin
• Timers
• Beakers/measuring jugs

Safety:

• Make sure the children keep a safe distance or else wear safety goggles in case the canister hits them.

Instructions:

• Have the children split up into groups and hand out safety googles if you have them. Tell the children we are going to build our own small rockets! And try to figure out which one will take off the fastest. But instead of using rocket fuel, we are using fizzy (Alka-Seltzer) tablets and water.
• Ask the children to predict how long it will take for our rockets to take off. Give each one a film canister and beaker/measuring jog, asking them to fill up the canister with 10ml of water.
• Hand out half a tablet while telling them not to drop it in the water until you say.
• Drop the tablets into the canister, close the lid, turn them upside down in the tub and have the children start the timer.
• Record how long it takes. Get the children to evaluate the results in comparison to their prediction.
• Repeat the experiment with 20ml of water and again, have them predict and work through the scientific process.
• The power in these little rockets is so small so you can imagine how big and how unbelievably powerful rockets that go to space are!
• This works horizontally too, if you want to get a car to zoom really fast along the ground use rockets.

How it works:

When you add the water to the canister it starts to dissolve the tablet and creates the gas carbon dioxide. As the carbon dioxide is released, it creates pressure inside the film canister. The more gas that is made, the more pressure builds up, until the cap it blasted down and the rocket is blasted up. This thrust system is the same workings behind a rocket. A similar build-up of pressure from gases is also what causes volcanic eruptions.