‘I’m not a Scientist!’ – Rainbow Activity 2: Chalk Pathway

By Farhin Begum

Welcome to the second blog in this series of “I’m not a Scientist!”

As we make our journey through the world of science fun and excitement, I have this activity for you that will not let you down.

This contains very few ingredients and is very messy so it is suitable for outdoor use only!


CC-BY science made simple.

What you need:

  • 5 different coloured paints
  • Bicarbonate of Soda
  • Plastic sandwich bags
  • Corn Flour
  • A teaspoon
  • Measuring jug
  • Vinegar
  • Bowl




Step 1- Mix it well

Get your jug and add 230 ml of white vinegar, one teaspoon of paint and 5 teaspoons of cornflour then mix well.

After you have done that, carefully add it in your plastic bag, but do not seal it yet, and place in the bowl.

Repeat this until you have all the different colours in bags stacked up in the bowl.


CC-BY science made simple


Step 2 – Step into the garden

Go outside and find a suitable place to do this.

Carefully get a bag and pour in 2 teaspoons of Bicarbonate of Soda and then quickly seal the bags and stand well back!


CC-BY science made simple


Step 3 – Expanding!

They will take a few minutes to fully expand and pop.


CC-BY science made simple


Step 4 – Sit back and watch

Sit back and watch the the stream of chalk running down your pathway! The chalk will wash away with a bit of rain or a spray with the hose.


CC-BY science made simple


The bicarbonate of soda reacts with the vinegar and produces a gas called carbon dioxide. The carbon dioxide, CO2, builds up in the bag because it can’t escape. Eventually there is so much pressure inside the bag from the build up of CO2 that the bag pops and the frothy, colourful chalk spills out down your path!

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Posted in Activity, Chemistry, Exploring Science, Primary