Continuous Rates Experiment Using Colorimetry – Propanone and Iodine

A detailed visual resource exploring how colorimetry can be used to follow the rate of reaction between propanone and iodine, catalysed by hydrochloric acid.

The poster takes students through the complete experimental process, including preparing iodine standards, selecting and zeroing a colorimeter, measuring absorbance and constructing a calibration graph of absorbance against iodine concentration.

It then shows how absorbance measurements taken during the reaction can be converted into [I₂] against time data. The approximately linear decrease in iodine concentration demonstrates that the reaction is zero order with respect to iodine, so the gradient gives the reaction rate directly.

The final section extends the investigation by varying the concentrations of propanone and hydrochloric acid while keeping the total volume constant. Students can see how doubling either concentration doubles the gradient and hence the rate, leading to:

Rate = k[CH₃COCH₃][HCl]

The resource also clearly distinguishes between the initial rates method and the continuous rates method.

Suitable for A-level / GCE Chemistry, particularly teaching experimental kinetics, reaction orders, rate equations, colorimetry and data analysis.

An accompanying animated version makes the resource particularly useful for classroom explanation, revision or independent study.