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Beer’s Law

Hands-On Labs, Inc.
Version 42-0140-00-03

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 2: Beer’s Law Curve and Unknowns

Data Table 1. Concentration and Resistance.

Tube Label	Concentration of Blue Dye in Test Tube (M)	Resistance Reading on Colorimeter (Ω)
	2.57 x 10-4 M	27.4
		25.7
		22.9
		20.6
		17.6
		13
		9.6
		6.7
		4.2
		2.6
	0 M	1.7
CD 1		10
CD 2		4.1

Graph 1. Plot of Concentration vs. Resistance.

Plot

Questions

Describe possible sources of error in this experiment.

The remainder of these questions are based upon the following scenario:

A testing laboratory has been hired by a company called “Drug Company Q” to analyze a series of over-the-counter drugs that the company produces. In these over-the-counter drugs, the active ingredient is called “Active Ingredient M.” The laboratory technician collected the following data from samples with known concentrations of the Active Ingredient M. That data is shown below in Table 2. Convert %T to absorbance (A=2-log(%T)) and prepare a Beer’s law plot using this data.

Table 2. Known Concentration of M Drugs.

Sample Identification Code	Sample Concentration (M)	%T
Q5000	4.00 x 10-4	17.9
Q5001	3.20 x 10-4	25
Q5002	2.40 x 10-4	35.7
Q5003	1.60 x 10-4	50.2
Q5004	8.00 x 10-5	70.8

The technician also collected absorbance readings for the 5 over-the-counter drugs for review. The data collected for the 5 over-the-counter drugs is shown in Table 3.

Table 3. Absorbance Data for Over-the-Counter Drugs.

Sample Identification Code	%T
M21050-1	43.7
M21050-2	44.1
M21050-3	45.8
M21050-4	42.1
M21050-5	30.1

Create a Beer’s law plot and best fit line for the data in Table 1.
Use the Beer’s law plot and best fit line to determine the concentrations for samples: M21050-1, M21050-2, M21050-3, M21050-4, M21050-5.
The company reported that sample M21050-2 has an M concentration of 0.0003M. Assuming that the results in Question C are 100% accurate and without error, is the company’s statement accurate? What is the percent error between the reported concentration and the concentration calculated in Question C?
By law, Drug Company Q must have an M concentration between 2.85 x 10-4 M and 3.15 x 10-4M. Do all samples analyzed meet the legal requirements? Use the information from Question C to explain your answer.