Chem 151 Week 8 Practical Midterm Exam - University of Arizona

Chem 151 Week 8
Practical Midterm Exam

“'It is a capital mistake to theorize before one has data. Insensibly one
begins to twist facts to suit theories, instead of theories to suit facts.”

—Sherlock Holmes
Consulting Detective

The practical is designed to assess the skill and knowledge of the chemical laboratory that you have
acquired so far this semester. You are presented with a problem to solve using your chemical laboratory
skills. As a pre-lab activity you are to describe how you plan to go about solving the problem. Once you
are in lab you will conduct experiments to collect data on the problem then write a report summarizing
your discoveries.

Unlike all other experiments performed in Chem 151 this will be an individual effort. Once experimental
work has commenced, you will not be allowed to collaborate with other students. In addition, you should
expect to be graded on the results you report.

Educational Objectives: A student who has successfully completed this experiment will demonstrate
an understanding of basic chemical principles presented in the course,
the ability to perform basic laboratory operations,
the ability to evaluate the quality of data collected in the lab
the general ability to work safely and efficiently in the lab, and
the ability to write a suitable report.

Experimental Objectives: A student who performs this experiment is asked to
determine the dye composition of an ink sample.
determine the presence of lithium in a sample.
write a suitable report.

The Problem: CSI Old Main

A bomb has been discovered in the basement of Old Main. The highly professional bomb squad
from UAPD has successfully disarmed the bomb and now the detectives are trying to determine
who planted it. Residue found on the bomb promises to provide useful information. The
material has been sent to the Arizona DPS crime lab for analysis.

The detectives have a suspect and have collected certain materials
from that person’s apartment. They have asked you to determine if
these materials are the same as the residue found on the bomb. In the
apartment they have discovered an ink pen they believe may match the
ink residue found on the bomb. They also discovered what they
believe to be bomb making ingredients. One of these is a salt.
(Remember that “salt” is the chemical name for any inorganic material
composed of a cation and an anion.)

Overview

The detectives provide you with a sample of the ink and a sample of the salt. They also provide
you with a copy of the analysis report on the bomb residue (below). You are to analyze the
materials and determine if they match the materials described in the report. You have access
(and are expected to use) the various materials and techniques employed so far this semester in
Chem 151.

Materials and Reagents

Materials

your locker Reagents

Red Tide spectrometer Ink sample

TLC strips Ethyl acetate

Open ended capillary Ethanol

tubes 0.1 M lithium chloride

Procedure

Four different solutions are provided as samples. Your instructor will assign you one to use.
It is up to you to create the procedures you will use in the lab. Your procedures should take into account
the following.

TLC. You will be provided with a TLC strip. It should fit into a large test tube. A piece of parafilm can
be used to cover the test tube. Capillary tubes are available for the spotting.

Emission Spectroscopy measurements. As with the emission spectroscopy experiment you will have a
spectrometer and knowns to work with. You will have to work with your classmates who provide laptops
to run the Logger Pro program to collect data.

Clean up. The TLC strip can go in the garbage can. Capillary tubes are glass waste.

Your Report

Once you have completed your analysis you are to write a report to the detectives describing your results,
your conclusions regarding the evidence and your recommendations. Your report MUST be written on
the worksheet form. You will attach your notebook entries to the worksheet. This report will be
evaluated as all reports this semester with an emphasis on the quality of your data presentation, the
credibility of your arguments, whether or not your conclusions are supported by the data you collect and
whether or not your recommendations are appropriate. This report is to be submitted at the end of class.

Link to the worksheet:

http://slb.faculty.arizona.edu/sites/slb.faculty.arizona.edu/files/151/practicalmidtermworksheet.pdf

State of Arizona
Department of Public Safety
Scientific Analysis Bureau

Case # : 001445-83d-2014

Case Description: Suspected bomb

Investigating Agency: University of Arizona Police Department.

Investigating Officer(s): Det. C. Lewis, Det. N. Bohr

Analysis Performed By: Dr. Bunsen Honeydew

Date Analysis Performed: February 19, 2014

Sample Analyzed
Sample consisted of a solid material composed of a red powder with
evidence of some white crystalline content.

Thin Layer Chromatograpy.
The liquid sample was subjected to TLC. A plastic backed silica gel
TLC strip was used. The developing solvent was a mixture of ethyl
acetate, water and ethanol.

The sample gave three spots. Blue spot with a Rf value of 0.21
Emission Spectroscopy Test. Red spot with Rf value of 0.35
Yellow spot with Rf value of 0.85

The solid sample was dissolved in water and subjected to emission

spectroscopic analysis. The results indicated the presence of

lithium.

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