Is the secretary guilty?

This resource accompanies the Education in Chemistry article Cold case chemistry, where you can read about how advances in forensic science are helping to solve crimes from the past.

The practical investigation is part of the In search of solutions collection which consists of a series of problem-solving activities designed to contextualise chemistry and engage learners in small group work. Visit this page for further tips and suggestions on how to use this collection of resources.

Learning objectives

1. Use your knowledge of physical and chemical changes to design an experiment to analyse a sugar sample.
2. Collect your evidence by making careful observations while carrying out your experiment.
3. Write an investigation report including what you did, your results and conclusion.

How to use

This activity falls into three parts: planning, carrying out the investigation and report writing. It fits nicely into the curriculum where students learn about separating mixtures using techniques such as dissolving and solubility, filtration, evaporation and crystallisation. In order to design their own experiments, learners need to be familiar with these techniques as well as being aware of the differences between physical and chemical changes.

The teacher notes include possible approaches to scene-setting, planning and practical work for the investigation. The technician notes include the equipment list, safety notes, preparation and disposal advice.

Write up and assessment

After collecting their evidence, learners produce a group report using the headings:

• Problem
• Method
• Results
• Conclusion

An optional exam-style question, with a structure strip, is included at the end of the student sheet. This question gives learners an opportunity to further demonstrate their knowledge and understanding of how chemical tests can be used to identify an unknown sample.