School of Physics Lecture Demonstration Manual

Hg-1 Chemical Clock A+B

Published: Wednesday 06 June 2007 - Updated: Monday 28 March 2011


To demonstrate a cyclic chemical reaction, the Belousov- Zhabotinskii reaction.



Chemical Clock A

Chemical Clock B


 To make Solution A: 

Dissolve 38.41g of Malonic acid in 400-600ml of water

Stir then add water in a volumetric flask to make 1L

 To make solution B: 

Dissolve 32.26g of Malonic acid in 400-600mL of water

Add 7.021g of potassium bromide

Add water to make 1L of solution in a volumetric flask.

 To make solution C:  

Dissolve 10.412g of ammonium cerium (IV) nitrate in 400mL of water. Stir

Add 150mL of concentrated sulphuric acid slowly as solution will heat up

Stir and allow to cool to room temperature.

Add water in a volumetric flask to make 1L of solution.

Solutions will store in sealed containers for a few weeks without degradation.

 Solution D is off the shelf: 

 Clock Procedure  

In a 1 Litre Flask add 300mL of solution A to 300ml of solution B.

Wait until solution clears.

Add 300mL of solution C.

Wait till solution fades to yellow Cerium colour

Add 3.6mL of solution D.

The chemical clock reaction should commence with the solution cycling through green purple red blue and back with about an initial 60 second total cycle time.

 Concentric circles 

Add 2.5mL of Solution A and 2.5mL of solution B to a Petri dish

Add 2.5mL of solution C to the dish

Add 1mL of solution D

Mix well

Concentric rings should develop after 1 minute.


Chemicals A, B and C can be prepared and stored for up to a year in sealed containers.

Safety notes

Chemical Safety 


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