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	Forensics Case 9 Killer Cup of Coffee: Using colorimetry to determine concentration of a poison

Activity Overview

In this activity, students will use colorimetry to determine the concentration of a colored species in a solution and use a linear relationship to model Beer's law. They use Beer's law to determine the concentration of iron(III)thiocyanate (FeSCN2+) in an unknown solution.

Before the Activity

Use TI Connect™ to download Vernier EasyData™ application

Connect the Colorimeter to Vernier EasyLink. Connect EasyLink to the USB port of the calculator

Set up the calculator for data collection and calibrate the colorimeter using blue light

See the attached PDF file for detailed instructions for this activity

Print pages 80 - 84 from the attached PDF file for the class

Print sample data and student work pages

Activity Downloads:

(file types)

During the Activity

Distribute the pages to the class.

Follow the Activity procedures:

Pour 30 mL of deionized water and 50 mL of ferrous thiocyanate solutions in two separate 50 mL beakers

Use a pipette to measure required amounts of water and FeSCN²⁺ solution and prepare 5 standard solutions

Fill the cuvette with solution, place it in the colorimeter, record the absorbance reading at 470nm

Record the absorbance readings for the standard solutions, blank, and unknown solution

Observe the graph of absorbance versus the concentration of FeSCN²⁺ solution

Find the equation of the line of best fit

Use the equation of the best fit line to estimate the concentration of FeSCN²⁺ in the unknown solution

After the Activity

Students analyze the results and answer the Case analysis questions on the Evidence Record sheet.

Review student results:

As a class, discuss questions that appeared to be more challenging

Re-teach concepts as necessary

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Subject Area:
Science : Forensics : Data Analysis
Science : Chemistry : Stoichiometry and Mole
Math : Geometry : Lines
Science : Chemistry : Solutions

Author:
Texas Instruments