Once students have created carbon dioxide from marble chips and acid, they can then test for carbon dioxide’s reaction with barium hydroxide by observing the carbonate precipitate

In this experiment, students will create carbon dioxide using marble chips and acid. They can then test for its reaction with barium hydroxide, observing the carbonate precipitate as they do so. 

This practical should take 20 minutes.



  • Student information sheet and worksheet
  • Clear plastic sheet (eg OHP sheet)
  • Plastic petri dish (base + lid), 9 cm
  • Plastic pipette
  • Scissors


  • Solutions contained in plastic pipettes, see our standard health and safety guidance.
  • Hydrochloric acid, 1 mol dm—3
  • Barium nitrate solution, 0.2 mol dm—3
  • Sodium hydroxide, 0.5 mol dm—3
  • Small marble chips

Health, safety and technical notes

  • Students must wear suitable eye protection (Splash resistant goggles to BS EN166 3).
  • Hydrochloric acid, HCl(aq), 1 mol dm–3, is of low hazard (see CLEAPSS HazCard HC047a).
  • Sodium hydroxide, NaOH,  0.5 mol dm–3 is corrosive (see CLEAPSS HazCard HC091a). Reducing the concentration to 0.4 mol dm-3 means it is an irritant with less of a requirement for goggles.
  • Barium nitrate, Ba(NO3)2, 0.2 mol dm–3  (s) is a skin/eye irritant (see CLEAPSS HazCard HC011).


  1. Cover the worksheet with a clear plastic sheet.
  2. Place the base of the petri dish directly over the circle provided. Place the reaction vessel in the centre.
  3. At the corners of the triangle add drops of the test solutions as indicated below (Care: barium nitrate is toxic).
  4. Put a small marble chip in the reaction vessel and add three drops of hydrochloric acid. Quickly replace the lid on the petri dish.
  5. Record all your observations over the next 15 minutes.

Teacher notes and test results

  1. The barium nitrate and sodium hydroxide drops should show no change.
  2. The barium nitrate and sodium hydroxide mixture should turn cloudy owing to the formation of the very insoluble barium carbonate from the reaction of the (acidic) carbon dioxide gas with (alkaline) barium hydroxide.
  3. The action of hydrochloric acid on marble chips generates carbon dioxide: CaCO3(s) + 2HCl(aq) → CaCl2(s) + CO2(g) + H2O(l)