It was a warm, sunny afternoon, when they crept inside…  Mom!  We’re boooored!  I wanted to avoid the iPods or Netflix, so I scraped together supplies to make homemade baking soda/vinegar rockets to shoot off in the backyard.  Holy cow!  Lots of rocket FAILS that day!   I may still stink like vinegar…   After working through different materials, we came up with our favorite combination and the kids learned more about acid/base reactions.  In this post, we walk through how our kids learned how to build an Alka-Seltzer rocket.  What’s also great about this project is that it can be easily turned into a science fair project… let’s SCIENCE!!

SHORT VERSION OF THE EXPERIMENT (tl;dr):  your kiddos will learn how to make a rocket using an empty 35mm film canister  “powered” by Alka-Seltzer and water.  Not a rocket scientist?  NO PROBLEM!  You can pull this off with most of the items already in your house, a trip to the dollar store, or of course, Amazon.  The experiment is probably best suited for 3rd graders and up, and beyond the basics of experimental design, they will learn about chemistry (acid/base reactions), physics (propulsion, motion), and the scientific method.  Basic data analysis (counting, comparing) can be used and if you snap some pictures along the way, during the construction and “launch”, setting up a science fair project board can be done in super easy fashion (like a single day)!

Edit: We recently learned a team at the University of Minnesota broke a Guinness World Record by blasting an Alka-Seltzer powered rocket 430 feet high!!! Whoa!!

Science fair project overview:  what we’ll do

Build an Alka-Seltzer rocket

Hey STEMium readers!  In this project, you’ll be comparing different “rocket fuel” combinations for our homemade rockets to see which one flies the highest.  You will construct your rocket out of an empty 35mm film canister, paper/cardboard and other accessories as needed (who DOESN’T want a glitter fin??).  Then, you’ll use different ratios of our “rocket fuel” mix:  Alka-Seltzer in water.  Some rockets will get a lot of Alka-Seltzer.  Others will only get a little Alka-Seltzer, so we can see if more means a bigger liftoff.  Get ready to get messy as this one may leave some spills.  If you’re going to do it indoors (not recommended), you’ll need a tarp, really high ceilings (like in a gym) and possibly a mop/cleanup crew.

Who can do this project?  Age range: 3rd Grade and up

We first did this experiment with a 2^nd grader, a kindergartner, and a preschooler.  Later, we turned it into one experiment center at a science night out for 3rd-6th graders.  Looking at all the grade settings, I think the concepts were a bit more challenging to convey to the younger groups (although they definitely enjoy the launches!).  It would probably be better suited for older kids – 3^rd grade and beyond.  Younger kids can still participate and help design/build the rockets.

 

The Science Behind The Alka-Seltzer Rocket

Before we delve into the details of the experiment, let’s talk more about how we’ll get our rocket to blast off.  There is so much science goodness packed into these experiments it’s hard not to get too excited!!

The chemistry of alka-seltzer

We will be taking advantage of ACID/BASE reactions.  Specifically, our rocket fuel of choice will be a combination of Alka-Seltzer and water.  While we’ve experimented extensively with baking soda and vinegar, the bottles and general setup is a little more hit or miss (and waaaaay messier).  I’ll put some links in the appendix if you’d like to try to compare “rocket fuels”, but for now we will stick with building an Alka-Seltzer rocket.

 

A chemical reaction is occurring whether you use baking soda/vinegar or Alka-Seltzer/water — an acid and base reaction, to be exact.  There’s some great background info from Khan Academy on acids/bases for more info, but the simplest explanation is that ACIDS are materials that have a lot of hydrogen ions (H+)…  When an acid is combined with a BASE (a substance with a lot of hydroxide ions, OH-), we call this an acid/base reaction and the end result is usually the generation of a salt and water (and especially important in our case — carbon dioxide gas!).

Mixing acids and bases – how does alka-seltzer work?

As you can see from this picture, when you open the Alka-Seltzer package, it looks like a simple tablet.  Digging deeper, Alka-Seltzer is a combo product, meaning it contains both an ACID (anhydrous citric acid) and a BASE (sodium bicarbonate).  The “anhydrous” part means that it has no water…hence, why it’s individually packaged to keep moisture out.  When you drop the tablet into a glass of water, the acid/base reaction can begin as the two reagents (citric acid and sodium bicarbonate) come together.  The picture below shows what’s going on in the chemical reaction… by combining this acid and base, we create water, a salt (sodium citrate) and carbon dioxide (CO2).

Now, why is carbon dioxide important???  Carbon dioxide is a gas.  We breathe in oxygen, and exhale carbon dioxide (CO2).  More on this in a second, but let’s think about our rocket for a minute…  we will combine the Alka-Seltzer (our acid/base) inside a closed container with water…  as the CO₂ builds up inside our rocket canister, it increases the pressure until it can’t hold it in anymore and BOOM!! the rocket explodes.

How Does The Rocket Take Off?

Back in 1686, Sir Isaac Newton formalized the key laws of motion… Newton’s third law is directly evaluated in our Alka-Seltzer rocket experiment:

<<For every action, there is an equal and opposite reaction>>

Check out this video below from Khan Academy for a good breakdown on Newton’s laws:

At this point you might be asking:  What does this mean and what does it have to do with bottle rockets??  Well, when the CO2 pushes out of the rocket, the rocket pushes away from the gas.  Gravity is another force pulling the rocket, keeping it on the Earth, but when the force of the gas pushing the rocket becomes greater than gravity, the rocket lifts off.

 

Materials – what you’ll need:

• Alka-Seltzer tablets – pop, pop, fizz, fizz. You are looking for the original effervescent tablets that fizz when dropped in water.  Not the chews.  Not the flavored kind.  You can try this link here.  We did not try Alka Seltzer Gold in our rockets, which contains two antacids (sodium citrate, potassium citrate) instead of just the one; however, I think it would most likely work the same.  Store brand product would also likely work out well.  Ideally, you want fresh material versus something that’s been sitting in a medicine cabinet for the last few decades.
• Water.   Just plain old water.  If you’ve got a tap (or bubbler as the fine folks of Milwaukee call it) then you are all set.
• Film canisters with lids – if you have some laying around the house, feel free to use any container that has a lid which will snap shut. If you’re like us though and haven’t used any film in the past decade, then cruise on over to Amazon.  We found this 12-pack of containers which should do the trick.  The seal that the lid makes with the container is important for the pressure to build up in the canister…so if you see people mentioning a flimsy lid, or poor seal in the reviews on Amazon, AVOID it and make a different selection.
• Construction paper/thin cardboard/index cards, scissors, markers/crayons, tape. The art supplies will be used to create the cone and fins on the rocket.  Get creative… if there are other lightweight materials that the kids are interested in adding (e.g. maybe glitter? Tinfoil?) go for it.
• Paper towel. Not necessary for the experiment but should make clean up a lot easier.
• Plastic drinking straws (optional). We added these to our Alka-Seltzer rocket to work as a tripod landing gear — basically, the rocket stood on these three legs like a stool.  It just kept the bottom of the rocket (“top of the film canister”) off the ground at launch.  You can also use cardboard triangle cutouts to make fins.

Designing the Experiment:  Picking a Hypothesis

Like our other experiments, it all starts with selecting a hypothesis….  Remember, we will vary the amount of Alka Seltzer used in our rockets and compare which one blasts off the most.  What do we think will happen?

 

 

Experimental Controls

This is a bit more challenging than our “Germiest Spot in School” experiment.  In that one, we had negative controls (bacterial plates with NO growth) and positive controls (bacterial plates with COMPLETE growth).  For our rocket experiment, one negative control might be a rocket with only water (but it’s kind of a bummer because it’s something that won’t fly).  Positive controls are a little trickier to come by though.

 

CHECKPOINT:  At this point, you should have a hypothesis about which rocket will fly higher, and why.  You may also have a few other variables you are testing… here’s what we wrote down:

• Hypothesis: the Alka-Seltzer rocket with a full tablet will fly further than the baking soda rocket
• Variable – Alka Seltzer: we made one rocket with a ¼ of a tablet, one rocket with a ½ of a tablet, one rocket with one full tablet, and one rocket with a tablet all ground up.
• Controls: you can do a negative one if you’d like.

Here’s our grid:

Rocket #	Amount of Water	Amount of Alka Seltzer tablets	Observations - how far it flew
1	half full	1/4 tablet
2	half full	1/2 tablet
3	half full	1 tablet
4	half full	1 tablet (crushed)

Methods/Procedure – How we’re going to complete our rocket build:

The steps listed below are how we completed our rocket project as an experiment; but please note, we did not enter this one as a science fair project.  You should be able to do this one as either approach — if you will be turning it into a science fair project, make sure you taking good notes and pictures to document everything.   In terms of how long it will take you, there’s about 15-30 minutes of setup/prep time (this is mostly designing the rocket — the creative part of the project), about 30 minutes for setting up reactions and launching rockets, and about 30 minutes to compare launches and analyze the data.  Assuming you have all the materials you need, you could get this one done in a single afternoon.

 

Time to build:  Alka-Seltzer rocket…

1. Creative time! Decorate the rocket.  The opening of the film canister will serve as the bottom, so it will be firing with the lid end on the ground and the bottom end on top.  Cut enough construction paper to wrap around the film canister and decorate however you’d like.  Use the tape to stick onto the container.  Also create a rocket nose cone out of paper and tape to the “top” of the rocket (“bottom of the film container”).  If you’d like to create fins, you can also add those on.  You can also now fix on your rocket “legs” with the straws by taping three to the sides.  Make sure the rocket can stand upright and doesn’t tip over.
2. Launch prep. Turn the rocket upside down to load the water in the container… fill it ~1/4 to ½ of the way full.  Make sure to note HOW MUCH water you added, so you have your combinations ready to test (look back at your chart if you need to keep track).
3. LAUNCH***need to move quickly here!***. Break an Alka Seltzer tablet in half (or fourths or leave whole, depending on which tube you are loading) and add the tablet in the container with the water.  QUICKLY!  CLOSE THE CONTAINER – make sure to snap the lid on completely.  Set the rocket on the ground upright (lid side down at the ground).  Stand back and count down the launch.
4. BOOM! Use a landmark or object to gauge how high the rocket made it.  Mark it down in a notebook or sheet of paper.  Also note how much “rocket fuel” was used – was it half a tablet and half full with water?

Data Analysis – What does the data tell us?

Congratulations!  You’ve officially built and launched rockets!

Hopefully, you’re not completely covered in a mess at this point and you have had some successful launches!  Which rocket flew the farthest?  Were any duds?  Was your original hypothesis correct?  How about testing the different variables – did adding more Alka-Seltzer to the rocket create a more powerful rocket?  If you did multiple rockets of the same kind (“replicates”), did they all fly the same or did some work better than others?

 

Your data analysis table might look something like this:

Rocket #	Amount of Water	Amount of Alka Seltzer tablets	Observations - how far it flew
1	half full	1/4 tablet
2	half full	1/2 tablet
3	half full	1 tablet
4	half full	1 tablet (crushed)

Conclusions – what we learned from the Alka-Seltzer rocket experiment; did it work?

Hopefully, the kiddos have a good idea about which rocket worked better or best. Hopefully, they also have a general understanding of what happens when you combine an acid and a base.  Most importantly, hopefully they had fun!!

Other things we’ve tried

After some fine tuning, we originally incorporated Alka-Seltzer rockets at a STEM outing and based it off of the Alka Seltzer science experiments site.  Overall, our rockets blasted off pretty easily with the majority successfully reaching some pretty good heights.

Now, separately, we have also tried the baking soda/vinegar rockets at home one summer day, but after getting drenched in about a gallon of vinegar we eventually abandoned our efforts that were based on this posting that we found using empty water bottles and a soda bottle.  While we had plenty of bottles, and we were even able to make the baking soda packets pretty easily, we struggled with corks that could fit tightly enough in the bottles.  The result:  tons of messy spills and leaks.  No takeoffs and bored kiddos.

While the baking soda/vinegar rockets will likely give you a bigger “boom”, they’re definitely more challenging to set up… from the starter perspective, if this is your first time, I’d opt for the Alka Seltzer/water setup in the film canisters to save your sanity.  Hands down – the Alka-Seltzer rocket strategy was far easier to maneuver and to keep the kids engaged.

 

Our results

As you can see from some of the pictures here, our Alka-Seltzer rocket with the most tablets flew the farthest.  As we increased the amount of Alka Seltzer in the container, we definitely noticed a stronger reaction taking place.  Interestingly, we couldn’t get much of a pop with the ground up tablet rocket.

Next steps – what are some follow up experiments?

There are a TON of different variables you can experiment with in the Alka-Seltzer rocket projects, which makes it fantastic to use for a science fair project.  Here are a few concepts/variables to further explore:

• Different solutions (besides water). What if you dissolved the Alka-Seltzer tablets in something besides water?  How would the reaction proceed if it were an acidic solution like orange juice? Vinegar?
• Different temperatures. What if you added ice, cold water to the container?  Would it change the intensity of the blastoff?  What about hot water?

 

Resources:

• NASA – parts of a rocket
• https://media.nationalgeographic.org/assets/file/Seltzer_Rocket_Lab_Activity.pdf
• Check out the original Alka-Seltzer site to get great ideas and pics for not only the Alka-Seltzer rocket, but other Alka-Seltzer-based experiments:  https://www.alkaseltzer.com/science-experiments/