You’ve been hired! A chemical research division needs your help in developing a new reaction process

Investigate the reaction rate, improve with experimentation, and draw the new machinery necessary.  

This experiment should take 70 minutes.


  • Eye protection
  • Beakers
  • Conical flasks
  • Bungs to fit them with a glass through tube
  • Rubber tubing
  • Gas syringes
  • Measuring cylinders
  • Stop clocks
  • Cotton wool
  • Balances (grams) to 2 decimal places
  • Graph paper
  • Calcium carbonate, marble chips approximately all the same size
  • Dilute hydrochloric acid, 4 mol dm–3

Health, safety and technical notes

  • Read our standard health and safety guidance here.
  • Wear eye protection.
  • Wear lab coats, or aprons if desired. 
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
  • Hydrochloric acid, 4 mol dm–3 HCl (aq), is a skin/eye irritant, see CLEAPSS Hazcard HC047a.

Possible approaches

It is important to tell students that the amounts of hydrochloric acid and water should be measured as carefully as possible.

The easiest way to compare the results from each part of the experiment is to construct a graph. Some students may follow the course of the reaction by observing the change in mass of the reaction mixture as carbon dioxide is given off.

Others may collect the CO2 given off in a gas syringe. “This challenge would make a good ‘design an experiment’ assessment for GCSE”.

Parameters such as stirring also need to be considered. 

Possible extensions

Examine effect of (i) particle size and (ii) temperature on rate of CO2 production – NB requires modification of student sheet.

Get students to draw a diagram of the plant, eg crushing machine, rollers etc.

Is the process continuous or batch? Other questions, eg waste disposal, can also be considered. 


  • Any remaining acid should be neutralised with weak alkali before being washed to waste.