Chemistry at the crime scene

This forensic science project should take approximately four to five hours to complete in full. It was initially created for 11–14 year-old learners but can be adapted to suit other age groups. 

Use the resource in a sequence of timetabled lessons, STEM clubs or during an activity day.

Learning objective

• Analyse observations to reach a conclusion.

Guidance notes

The activity requires learners to analyse several items of evidence collected at a fictional, local crime scene and can be adapted to reflect a scene local to the users. Find the evidence (EV) needed for each pair of learners, along with the reagents and equipment needed for the tests, in the technician notes. 

The student workbook leads learners through the forensic analysis at each station, encouraging them to record their observations and conclusions based on the evidence.

Station 1: screwdriver cast 

Learners should compare the screwdriver cast (EV1) with the photos of the suspects’ screwdrivers (EV2, EV3 and EV4). Take these photos and print them off in advance of the session. The pairs should record their observations and answers to the questions provided in their student workbooks.

Station 2: fingerprints

Learners should use the magnifying glass/fingerprint magnifier to compare the aluminium fingerprint lifts and the fingerprint cards from Suspect 1 and Suspect 2. They should use the guidance in the instruction sheet and record their observations in their student workbooks.

Station 3: white powder

In this activity, learners will use flame tests to determine whether the white powder found on either of the suspects was the same as the powder found in the victim’s house. Tell the learners the three white powders have been dissolved in water to form the solutions they are testing. The learners will place the pre-soaked splints into a blue Bunsen burner flame and record the colours of the flames produced, comparing them with the reference colours provided to determine the identities of the metals in the solutions they test.

Station 4: bloodstained clothing

Inform learners that chemical tests are often used to detect or confirm the presence of blood. Learners will carry out the Kastle–Meyer (KM) test on a swab taken from the baseball bat found in the garden of a house in a street near to the victim’s house (EV13), clothing from the victim (EV12), clothing from Suspect 1 (EV14) and clothing from Suspect 2 (EV15).

Learners may need support with this activity as it should be completed using a fume cupboard/fume hood, if available. If a fume hood is not available, set up this station in a well-ventilated area. See the Health and safety section for advice and suggestions to avoid the use of animal blood. 

Station 5: hair samples

In this activity, provide learners with three pre-mounted hair samples to examine under the microscope. One is a hair sample taken from the victim’s clothing (EV16), one is a hair sample taken from Suspect 1 (EV17) and the third is a hair sample taken from Suspect 2 (EV18). Learners will record their observations in their student workbooks and should be able to match the hair sample taken from the victim with that taken from one of the suspects.

Depending on time and interest, this can be made more or less challenging. For example, to reduce the challenge, the hairs used should be obviously different in colour and texture, or, to increase the challenge, the hairs used could be of similar colour but have different textures or pattern of scales.

Station 6: fibre samples

The station instruction sheet provides an overview of three types of fibres and their identifiable features. Learners can use this sheet to identify the type of fibre present, examining the samples under the microscope. One set is from the victim’s clothing (EV19), one set is from Suspect 1’s clothing (EV20) and the third set is from the Suspect 2’s clothing (EV21). 

Once they’ve completed all six stations, learners should make a conclusion as to which of the two suspects is guilty of the crime and how they can use their evidence to support this conclusion. The glossary sheet included in the student workbook may be useful for any learners who are unsure about some of the terminology used. Use the key terms quiz at the end of the workbook to assess learners’ recall of some of the techniques used.

Find the answers to all the activities in the teacher notes and on the slides. 

Health and safety

Read our health and safety guidance and carry out a risk assessment before running any live practical. 

The safety equipment suggested is in line with CLEAPSS requirements. For non-hazardous substances, wearing lab coats can help to protect clothes. The safety rules might be different where you live so it is worth checking local and school guidance. Learners should demonstrate precautions such as those that a crime scene investigator would take to avoid contamination of the evidence. This includes wearing safety glasses, gloves and a buttoned-up lab coat, when appropriate, and filling in an evidence continuity label on each evidence bag.

Station 4 involves the use of animal blood. Make learners aware of this before they start the practical and give them the option to avoid handling the clothing at that station. Any learners who do not wish to handle the clothing could collect the observations gathered from another group. This presents a good opportunity to discuss with the learners how forensic teams work with each other and the police to gather evidence when trying to solve crimes. If the use of animal blood is not a suitable option, find instructions to prepare an alternative ‘blood mixture’ in the technician notes.

Careers

The Chemistry for All project found that recognising the value and importance of chemistry, and appreciating how it can lead to interesting and well-paid jobs strongly related to learners’ future aspirations.

Use the job profiles embedded in the PowerPoint to introduce learners to four scientists who use their chemistry skills, knowledge and qualifications in their careers. Ask them to reflect on careers related to forensic science and the skills and knowledge needed for these roles in relation to their own interests. Share our careers website, A Future in Chemistry, with learners to discover the different study options available to them, find more job profiles of chemists making a difference and try our career options game.

Find more projects like this, plus shorter activities suitable for single science lessons or clubs on our Outreach resources hub.