Working scientifically – Alka-Seltzer Rockets!

By Becky Holmes

Using the “working scientifically” section of the Key Stage 2 curriculum, the science made simple team are going to scientifically……make an EXPLOSION!

If you want to get straight to the explosion, instructions are halfway down this page , but make sure you try the Challenge at the end and tweet us a picture of your attempt to @scimadesimple.

You will need:

you will need

You will need…. Photo: science made simple (CC-BY-NC)

For each group of four students working together.

  • 3 Vitamin C tubes (These can be found at most supermarkets)
  • 12 Alka-Seltzer tablets
  • Measuring jug
  • Shallow glass dish, or any container you can easily make observations in
  • 1m ruler


If it’s a sunny day, this experiment is perfect to perform outside. If it’s not, you’ll also need:

  • Plastic table covers
  • Large tray

Let’s do this!

Stage 1


Alka Seltzer tablet. Photo: science made simple (CC-BY-NC)

1. Place an Alka-Seltzer tablet into a bowl of water

What do you see?

-making systematic and careful observations

setting up simple practical enquiries

What happens?

….the tablets fizz, make bubbles, and crumbles.

Can you suggest anything else which may be happening? Describe it as scientifically as possible.

What is causing the bubbles? What is inside the bubbles?

What state of matter is the tablet? What state of matter is the water? What state of matter is produced by reacting them together?


Solid    Liquid    Gas    Reaction    Carbon Dioxide

Stage 2

– make predictions 

Repeat the enquiry but this time place the Alka-Seltzer tablet and water inside a closed tube.

Before you start, have a look at the instructions and discuss your predictions. What do you think is going to happen? Can you explain why that might happen? Use your observations from stage 1.


Instructions. Image: science made simple (CC-BY-NC)


Pressure         Explosion       Increase

Stage 3

-setting up simple practical enquiries, make predictions for new values, comparative and fair tests

-using results to draw simple conclusions, suggest improvements and raise further questions

Next repeat the enquiry using three tubes at once. Observe the height each tube reaches.

Did they all explode at the same time?

Do they all go to the same height? What could have caused this?

Was your test fair? Was each tube prepared exactly the same way?  Are there any improvements to make the test fairer?

Things to think about; Are all the tubes on the same surface? Is the same amount of water and tablet being added? How could you measure the water better?


Can you set off 5 Alka-Seltzer rockets in succession, each one going a bit higher than the next. What would you need to vary? Give it a try!

We would love to see your “in the air” results or hear what you tried, please tweet them to @scimadesimple or email to

Here are Bedwas High School students showing the rockets to Graig Y Rhacca Primary pupils, as part of a project funded by Will I Am and the Princes Trust. Why not use them as part of your next science event.

Curriculum Links

Key Stage 2:

  • Asking relevant questions and using different types of scientific enquiries to answer them
  • Setting up simple practical enquiries, comparative and fair tests
  • Making systematic and careful observations
  • using results to draw simple conclusions, make predictions for new values, suggest improvements and raise further questions
  • Identifying differences, similarities or changes related to simple scientific ideas and processes



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Posted in Activity, Chemistry, Primary
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