Fill your burette with a ’rainbow’ by using this practical that shows students the effervescent reaction between acid, sodium carbonate, and universal indicator

With a little universal indicator, acid, and sodium carbonate, students will be amazed by the effervescent reaction that causes a ’rainbow’ to appear. 

This experiment should take five minutes. 



  • Eye protection
  • Burette, 50 cm–3 
  • Retort stand with boss and clamp
  • Cotton wool plug 


  • Universal Indicator solution
  • Hydrochloric acid solution, 10 cm3, 2 mol dm–3
  • Sodium carbonate solution, 20 cm3, 1 mol dm–3

Health, safety and technical notes


  1. Clamp the burette vertically.
  2. Add 0.5 cm3 of the Universal indicator solution followed by 10 cm3 of the hydrochloric acid to give a clearly visible red colour.
  3. Add 20 cm3 of the sodium carbonate solution.
  4. Insert a loose plug of cotton wool in the top of the burette.
  5. The sodium carbonate and hydrochloric acid react, with effervescence, and the burette will be filled with liquid showing a ‘rainbow’ of all the colours of Universal indicator from red through orange, yellow, green and blue to purple.


Place the burette against a white background to show the colours to best advantage.