Chemistry Magic Trick

Posted on: 06/06/2022

Our wonderful KS3 chemists were in for a treat on the last day of term with a chemistry magic trick! Students explored the effect of changing the concentration of sodium thiosulfate solution on the rate (speed) of a reaction using an eye-catching colour change experiment called the iodine clock. During the reaction, two clear liquids are mixed, resulting in another clear liquid. After some time, the solution suddenly turns dark blue.

The reaction is called a clock reaction because there is a delay before the colour turns blue. This delay depends on the concentration of one of the starting materials (sodium thiosulfate in this case). Students were able to develop their own trick after working out how much sodium thiosulfate solution and water were needed to change the colour in a known time.  

This activity was a fun way to introduce students to factors affecting the speed at which a reaction is taking place. They will be looking at this in more detail in GCSE and A-Level Chemistry.  

A huge thank you to our Y12 scientists Sana and Pratik for their help!

Written by Ms Shuman