Try this investigation to explore irreversible changes and changing different variables

This resource is also available in Welsh and Irish

This experiment focuses on how materials change when they react together. First watch the ‘bath bombs’ demonstration video, then find out how your learners can use similar ingredients to explore an irreversible reaction. 

Learning objectives

  • To understand that chemical changes produce new materials and are irreversible.

Enquiry skills:

  • To take measurements.
  • To record data and results using scientific diagrams and labels.
  • To use test results to make predictions.

Watch the video

The video below shows how to carry out the ‘bath bombs’ demonstration.

Source: Royal Society of Chemistry

Make a bath bomb with your primary students to investigate gases, and changing materials.

Download the supporting materials

Set up and run the investigation with your class using the teacher notes and classroom slides, featuring a full equipment list, method, key words and definitions, questions for learners, FAQs and more.

Teacher notes

PDF | Editable Word document

Classroom slides

PDF | Editable PowerPoint document


What do learners need to know first?

Learners should already be familiar with:

  • States of matter (materials as solids liquids and gases).
  • Melting and freezing as reversible changes.
  • Dissolving as a reversible change.
  • Powders, which are solids in granular form.

Equipment list

Per pair/group:

  • Beakers/containers
  • Spoons/mixing implements of appropriate size or pre-measured amounts in cake cases
  • Pipettes (optional)/fine paintbrushes
  • Citric acid
  • Bicarbonate of soda
  • Water
  • Oil (rapeseed/baby oil) *allergies
  • Food colouring/essential oil for colour and scent *allergies
  • Salt
  • Stopwatches

As citric acid is not found in all supermarkets it may be easier to source online or where home brewing materials are sold.

Additional resources