Beer's law lab answer key

Hands-On Labs, Inc. Version 42-0140-00-04

Lawrence lovejoy

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 1: Colorimeter and Sample Preparations

Data Table 1. Concentration and Resistance

Tube Label

Concentration of Red Dye in the Test Tube (M)

Resistance for W blank (Ω)

Resistance for sample (Ω)

Overall resistance = sample resistance (Ω)/blank resistance (Ω)

B

1.99 x 10-4

5.02 x 103(Ω)

5.02 x 103

1

1

2.15 x 10-4

4.65 x 103

6.23 x 103

1.33

2

1.59 x 10-4

6.28 x 103

6.25 x 103

0.99

3

1.39 x 10-4

7.19 x 103

7.19 x 103

1

4

1.19 x 10-4

8.403 x 104

8.10 x 104

0.96

5

9.95 x 10-5

1.005 x 104

1.00 x 104

1

6

7.96 x 10-5

1.256 x 104

1.25 x 104

1

7

5.97 x 10-5

1.675 x 104

1.67 x 104

1

8

3.98 x 10-5

2.51 x 104

2.51 x 104

1

9

1.99 x 10-5

5.02 x 104

5.02 x 104

1

CD1

1.99 x 10-4

5.02 x 103

5.02 x 104

1

CD2

1.99 x 10-5

5.02 x 104

5.02 x 104

1

W

0

0

2

0

Data Table 2. Concentration and % Transmittance

Tube Label

Concentration of Red Dye in the Test Tube (M)

Resistance for W blank (Ω)

Resistance for sample (Ω)

Current for W blank (μA)

Current for sample (μA)

% T = sample current (microamps)/blank current ( μA ) x 100

B

1.99 x 10-4

5.02 x 10-3

5.02 x 103

5.02 x 10-3

5.02 x 10-3

100

1

2.15 x 10-4

5.02 x 10-3

6.23 x 103

5.02 x 10-3

6.23 x 10-3

80.57

2

1.59 x 10-4

5.02 x 10-3

6.25 x 103

5.02 x 10-3

6.25 x 10-3

80.47

3

1.39 x 10-4

5.02 x 10-3

7.19 x 103

5.02 x 10-3

7.19 x 10-3

69.86

4

1.19 x 10-4

5.02 x 10-3

8.40 x 103

5.02 x 10-3

8.40 x 10-3

59.79

5

9.95 x 10-5

5.02 x 10-3

1.00 x 104

5.02 x 10-3

1.00 x 10-2

50.23

6

7.96 x 10-5

5.02 x 10-3

1.25 x 104

5.02 x 10-3

1.25 x 10-2

30.07

7

5.97 x 10-5

5.02 x 10-3

1.67 x 104

5.02 x 10-3

1.67 x 10-2

31.31

8

3.98 x 10-5

5.02 x 10-3

2.51 x 104

5.02 x 10-3

2.51 x 10-2

20

9

1.99 x 10-4

5.02 x 10-3

5.02 x 103

5.02 x 10-3

5.02 x 10-3

100

W

0

0

0

0

0

0

Data Table 3. Concentration and Absorbance

Tube Label

Concentration of Red Dye in the Test Tube (M)

A = log (100/%T)

B

1.99 x 10-4

100

1

2.15 x 10-4

80.57

2

1.59 x 10-4

80.47

3

1.39 x 10-4

69.86

4

1.19 x 10-4

59.79

5

9.95 x 10-5

50.23

6

7.96 x 10-5

30.07

7

5.97 x 105

31.31

8

3.98 x 10-5

20

9

1.99 x 10-4

100

W

0

0

Exercise 2: Beer’s Law Curve and Unknowns

Graph 1. Resistance vs. Concentration

Plot

Graph 2. % Transmittance vs. Concentration

Plot

Graph 3. Absorbance vs. Concentration

Plot

Questions

A. Describe possible sources of error in this experiment.

Possible sources of error would be spilling of any substance to which would alter the outcome of each experiment, lack of attention to time and chemical reaction registration, as well as the use of the wrong chemicals.

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 all of these over-the-counter drugs, the active ingredient is called “Active Ingredient M.” The laboratory technician collected the data from samples with known concentrations of Active Ingredient M. The data is shown below in Table 2.

Table 2. Known Concentrations of Active Ingredient M Drug

Sample Identification Code

Sample Concentration (M)

Absorbance

Q5000

4.00 x 10-4

0.750

Q5001

3.20 x 10-4

0.602

Q5002

2.40 x 10-4

0.447

Q5003

1.60 x 10-4

0.299

Q5004

8.00 x 10-5

0.150

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

Absorbance

M21050-1

0.359

M21050-2

0.356

M21050-3

0.339

M21050-4

0.376

M21050-5

0.522

B. Create a Beer’s law plot and best fit line for the data in Table 2.

C. 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.

2.17 x 10-4 M

2.14 x 10-4 M

2.04 x 10-4 M

2.27 x 10-4 M

3.00 x 10-4 M

D. 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?

Assuming that the results in Question C are 100% accurate and without error, I think the company’s statement is inaccurate and the percent error between the reported concentration and the concentration calculated in Question C is approximately 39%.

E. 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.

There appears to only be one sample analyzed that meets the legal requirements needed which would be M20150-5 (3.00*10-4 M).

Question: What is spectroscopy and describe the different spectroscopic methods?

Spectroscopy is a study of the interactions between matter and electromagnetic radiation where electromagnetic radiation is composed of electrical and magnetic waves which oscillate on perpendicular planes. This specified range of wavelengths is allowed to pass through a sample containing a compound of interest (Chemistry LibreTexts, 2017). Typically light or mass spectra would be analyzed, where the spectrum of a source is used in order to determine the composition of a substance with the following methods: cirular dichroism, mass spectrometry, Raman spectroscopy, nuclear magnetic resonance spectrscopy, ultraviolet-visible spectroscopy, and Ultraviolet-visible spectroscopy (Hands-On Labs, Inc., n.d.).

The Beer’s law relates the absorption of light to the properties of the material where light travels and, given what we’ve learned through these exercises, it was obvious that the linear relationship between the absorbance and concentration with the use of plots and also visualizing the change in color with diluted dye and how the concentration of each sample is affected.

Reasoning: after concentration and absorbance was made possible, mostly with the use of visualization ,I saw a significant difference in color change with each added solution.

Transmittance vs. Concentration

Concentration of Red Dye in the Test Tube (M) 1.9900000000000012E-4 2.1500000000000008E-4 1.5899999999999999E-4 1.3899999999999999E-4 1.1900000000000009E-4 9.9500000000000074E-5 7.9600000000000037E-5 5.9700000000000042E-5 3.9800000000000012E-5 1.9900000000000012E-4 0 100 80.569999999999993 80.47 69.86 59.790000000000013 50.230000000000011 30.07 31.310000000000006 20 100 0
Absorbance vs Concentration

Concentration of Red Dye in the Test Tube (M) 1.9900000000000012E-4 2.1500000000000008E-4 1.5899999999999999E-4 1.3899999999999999E-4 1.1900000000000009E-4 9.9500000000000074E-5 7.9600000000000037E-5 5.9700000000000042E-5 3.9800000000000012E-5 1.9900000000000012E-4 0 100 80.569999999999993 80.47 69.86 59.790000000000013 50.230000000000011 30.07 31.310000000000006 20 100 0
Known Concentrations of Active Ingredient M Drug

Absorbance
Q5000

Q5001

Q5002

Q5003

Q5004

4.0000000000000018E-4 3.2000000000000024E-4 2.4000000000000009E-4 1.6000000000000009E-4 8.0000000000000034E-5 0.75000000000000022 0.6020000000000002 0.44700000000000001 0.29900000000000015 0.15000000000000005

Resistance vs. Concentration

Concentration of Red Dye in the Test Tube (M) 1.9900000000000012E-4 2.1500000000000008E-4 1.5900000000000007E-4 1.3900000000000007E-4 1.9000000000000012E-4 9.9500000000000074E-5 7.9600000000000051E-5 5.9700000000000055E-5 3.9800000000000019E-5 1.9900000000000009E-5 1.9900000000000012E-4 1.9900000000000009E-5 0 100 80.569999999999993 80.47 69.86 59.790000000000013 50.230000000000011 30.07 31.310000000000006 20 100 0 1 0