A bit of chemistry that all gravy, move an Oxo cube as fast as possible

Make sure you know which side of your table is buttered as you create a slick surface for your swift stock cube.


It is suggested that either:

An entire morning be devoted to the problem (e.g. on the last day of term), which would allow 2 h for practical activities and 30 minutes for judging 


The problem be given to the class as a homework exercise 2 weeks or so before the judging. Judging could then take place in a normal double science lesson, allowing 45 minutes for repair and final adjustments, and 30 minutes for judging. 


  • Items from the junk list to encourage creativity
  • The judges will require a stop watch or an arrangement with a computer and photocells if the Oxo cubes move too fast.

Materials per group

  • Sodium hydrogencarbonate (maximum amount = 3 level teaspoons)
  • citric acid (maximum amount = 9 level teaspoons)
  • Access to water
  • Butter/margarine to reduce friction

Equipment per group

  • Identical teaspoons (can be plastic)
  • Safety glasses. 

Health, safety and technical notes

  • Read our standard health and safety guidance here
  • Wear eye protection. 
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
  • For more information on sodium hydrogencarbonate see CLEAPSS Hazcard HC095a.
  • Citric acid is an eye irritant, see CLEAPSS Hazcard HC036c.


Some guidance may be needed for younger age groups – e.g. water is needed for the reaction. The reaction might be used to do the moving, or it could be used to start the movement – e.g. to trigger movement of a counterbalance


To increase the chemical content, the task could be extended by prior (or subsequent) experimentation, to select the best choice of gases/chemicals.


This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.