Chemical reactions of copper lab report

Lab Report Chemistry 1

A Beer’s Law Experiment

Introduction

Colored solutions have interested chemists for a long time. Of particular interest has been the fact

that colored solutions, when irradiated with “white” light, will selectively absorb light of some

wavelengths, but not of others. When this happens, the absorbed light disappears and the remaining

light (lacking this color) contains the remaining mixture of non-white light wavelengths. A color-

wheel (below) shows approximate complementary relationships between wavelengths absorbed

and transmitted. A green substance, for example, would absorb red light (the complementary

color). This is very useful for forensic and industrial procedures because it is non-destructive to

the sample and does not alter it in any way. Visible spectroscopy requires only shining light on the

sample and causes no change to the solution.

Image from: http://sustainable-nano.com/2015/07/07/fruit-colors/

We can determine the particular wavelength or group of wavelengths absorbed by exposing the

solution to monochromatic light of different wavelengths and recording the responses. If light of

a particular wavelength is passed through a sample and does not reach the detector, we will see

that the intensity of the transmitted light (I) is significantly less than the intensity of the light

incident on the sample (Io). The percent transmittance is then defined as the percent of the incident

light that passes through the sample such that

%T = (I/Io) x 100 (1)

The Beer-Lambert law shows that the molar solution concentration (c) is linearly related to the

log of the ratio of the transmitted and incident light, equation 2, where l is the length of sample

cell (usually 1 cm) and ε is the molar absorptivity, which is a constant for each particular

molecule.

log(Io/I) = εcl (2)

http://sustainable-nano.com/2015/07/07/fruit-colors/
This equation is often written in terms of absorbance (A), equation 3.

A = εcl (3)

With this equation (or a calibration curve based on it), you can determine an unknown

concentration or estimate what the absorbance of a certain solution will be as long as three of the

four values in the equation are known.

In the first part of this experiment, you will vary the concentration of your solution and make a

calibration plot of absorbance versus concentration. Beer’s law shows that absorbance is linearly

related to concentration.

It should be noted that there are conditions where deviations from Beer’s law occur. This happens

when concentrations are too high or because of lack of sensitivity of instrumentation.

In the second part of the experiment, you will determine the concentration of dye in a sample of

Froot Loops® cereal. Currently 7 non-natural food colorings are approved by the FDA (below).

Source: https://www.acs.org/content/acs/en/education/resources/highschool/chemmatters/past-issues/2015-

2016/october-2015/food-colorings.html

You will accurately weigh Froot Loops® containing a dye, extract the dye to make a solution and

measure its absorbance. Using the calibration curve you obtained in the first part, you can

determine the concentration of the dye from the graph.

Objectives

In this experiment you will:

● Measure the absorbance and wavelength of the dye stock solutions.

● Prepare and test the absorbance of four standard dye solutions.

● Plot a standard curve from the test results of the standard solutions.

● Measure the absorbance and calculate the concentration of dye solutions extracted from Froot

Loops® cereal.

https://www.acs.org/content/acs/en/education/resources/highschool/chemmatters/past-issues/2015-2016/october-2015/food-colorings.html
https://www.acs.org/content/acs/en/education/resources/highschool/chemmatters/past-issues/2015-2016/october-2015/food-colorings.html
Equipment, Chemicals and Supplies

Deionized water scoopula hot plate

100% Ethanol weigh boats (2) stir plate

50% ethanol/water solution large test tubes (4) SpectroVis

10 mL and 50 mL graduated cylinders test tube rack LabQuest

small beaker glass stir rod plastic cuvette

mortar and pestle magnetic stir bar small pipettes (2)

Erlenmeyer suction flask plastic tubing metal tongs

Buchner funnel filter paper (2) mass balance

Safety

a. Wear goggles and lab coat throughout the experiment.

b. Do not eat or taste the Froot Loops® supplied.

c. Chemicals/Solutions should be disposed of in the appropriate containers.

Procedure

Calibration

1. Connect a Spectrometer to the USB port of the Vernier LabQuest unit using the USB cable. Turn on the LabQuest unit.

View the video How to Start the Lab Quest Unit and Spectrometer for assistance.

(http://youtu.be/OCK1PbrZZEE)

2. Calibrate the spectrometer:

a. Prepare a reference (or “blank”) sample by filling an empty cuvette ¾ full with distilled water.

b. Wipe the sides of the cuvette with a paper towel to remove any fingerprints. Place the cuvette filled with water in spectrometer. Notice that the cuvette has two

different sides, a smooth side (left) and a ridged side (right). Make sure that the

smooth side with the arrow at the top is facing the side of the spectrometer’s cuvette

slot with the arrow and light bulb.

http://youtu.be/OCK1PbrZZEE
c. On the LabQuest unit, tap the reddish-orange meter box and select Calibrate. The following message appears in the Calibrate dialog box: “Waiting ... seconds for

lamp to warm up.” After the allotted time, the message changes to: “Finish

Calibration”.

View the video How to Calibrate the Spectrometer for assistance.

(http://youtu.be/S-Pu3G85kew)

d. Select “Finish Calibration”. When the message “Calibration Completed” appears after several seconds, select OK.

e. Dump the water out of the cuvette.

Part I. Learning about Beer’s Law

3. Use the pipette to fill the cuvette with approximately 3 mL each of the dye stock solution (red, blue, and yellow). Measure the solution’s absorbance and wavelength. Make sure you

wipe the cuvette clean before placing it into the spectrometer. Record the absorbance and

peak wavelength in Table 1 on the data sheet.

4. Dump the dye solution into the waste beaker at your bench. Rinse the cuvette with water thoroughly.

5. Repeat steps 3-4 with the remaining two dye stock solutions.

6. Choose one of the dye stock solutions to make dilutions.

7. Add 15mL of the chosen stock solution to a graduated cylinder and pour into a small beaker. Measure 50 mL of deionized water using a graduated cylinder and pour into another beaker.

8. Label four clean, dry, test tubes 1-4. Use a test tube rack to arrange them.

9. Prepare four standard solutions according to the chart below. Transfer the correct amount of dye solution and water into each large test tube. Thoroughly mix each solution with a stir

rod. Clean and dry the stir rod between uses. Make sure you don’t mix up your two pipettes.

Refill your 10 mL graduated cylinders with either solution or water as needed.

Test tube number Dye solution (mL) Deionized H2O (mL) Concentration (M)

1 1 9 0.1

2 2 8 0.2

3 4 6 0.4

4 5 5 0.5

http://youtu.be/S-Pu3G85kew
10. On the LabQuest, select the wavelength of light to analyze according to the chosen color (wavelength should be the same as in Table 1 on your data sheet).

See the video How to Measure Absorbance of a Solution for assistance.

(http://youtu.be/hvQ3_MqiNZA)

11. Measure the absorbance of each of the four standard solutions (follow the steps below for each solution).

a. With a clean pipette, add a small amount of one standard solution to the cuvette and shake the cuvette to rinse it. Dispose of this solution in a waste beaker at your bench.

b. Use the pipette to fill the cuvette with approximately 3 mL of the dye solution. Measure the solution’s absorbance and wavelength. Make sure you wipe the cuvette

clean before placing it into the spectrometer. Record the absorbance and in Table 2

on the data sheet.

c. Dump the dye solution into the waste beaker at your bench. Rinse the cuvette with water thoroughly.

12. After all four absorbance measurements are collected, graph the data in the Excel spreadsheet provided on Canvas. Enter the absorbance and concentration values. The Excel spreadsheet

will generate a graph and provide an equation for the line automatically.

13. Write the equation on your data sheet. Save the Excel file. You will need to include the plot in your lab report.

14. All waste generated from Part I of the experiment should be disposed of in waste container G.

Part II. Extracting Food Dye from Froot Loops® Cereal

1. Select four Froot Loops® for the primary color used in Part I and the corresponding secondary color according to the table below. Record the color chosen. You will complete

the following steps for both Froot Loops®. Do not eat the cereal.

Primary Secondary

Red Orange

Blue Purple

Yellow Green

2. Grind the rings of the colored Froot loop to a fine powder using a dry mortar and pestle. Pour the powder onto a weigh boat.

http://youtu.be/hvQ3_MqiNZA
3. Use a scoopula and measure 0.5 g of the powder in a tared small beaker using the mass balance.

4. Measure 15 mL of deionized water in a graduated cylinder and pour it into the beaker with the powder.

5. Using a hot plate on a setting of 6, heat the solution while stirring with a stir rod until it just starts boiling. Remove from the hot plate using metal tongs and let it cool. Turn off

the hot plate. While one partner is waiting on the heating, the other should move to step

6.

6. Repeat steps 2-5 with the secondary color

7. Once cool to the touch, add 15 mL of 100% ethanol to the slurry. Add a magnetic stir bar.

8. Stir the slurry/ethanol mixture on a stir plate for 5 minutes using a setting of 3. Then, let the solution settle for at least a minute.

9. Assemble the suction Erlenmeyer flask with the tubing to the proper vacuum opening in the water faucet. Ask your GSA if unsure. Place the filter paper inside the Buchner funnel

and place on top of the flask. The funnel is plastic (NOT GLASS), similar to that shown

below.

10. Acquire 10 mL of 50% ethanol/water solution before you begin filtering.

11. Turn on the water faucet the tubing is connected to.

12. Carefully pour the solution into the Buchner funnel to remove the solid from the solution.

13. Add the 10 mL of 50% ethanol/water solution to the beaker that contained the solid. Swirl the beaker and pour the solution into the Buchner funnel to filter.

14. If solid passes through your filter paper, filter the filtrate again to remove as much solid as possible. If no solid passed through, continue to step 14.

15. From the Erlenmeyer flask, collect 10 mL of the extracted dye solution using a graduated cylinder. Pour the solution into a small beaker.

16. Add 5 mL of the 50% ethanol/water solution to the beaker that contains the extracted dye solution. Mix the solution with a glass stir rod.

17. You must recalibrate the SpectroVis with 50% ethanol/water solution.

***Follow Calibration steps using the 50% ethanol/water solution instead of pure water.

Dump the solution into a waste beaker at your bench***

18. Add a small amount of your extracted dye solution from the small beaker to the cuvette. Shake the cuvette to rinse it. Pour the solution into a waste beaker at your bench.

19. Add 3 mL of the extracted dye solution to the cuvette and record the absorbance at the same wavelength you recorded the absorbance for the stock solution in Table 1 and 2 on

your data sheet.

20. Calculate the concentration of the extracted dye using the best-fit line equation from Table 2 and the absorbance you recorded.

21. You may dispose of all solutions from the color Froot Loops® you chose into the waste beaker. Rinse all of your glassware thoroughly. The waste can be disposed of in waste

container S.

Report: A Template for the report is provided on Canvas. Be sure to follow the instructions in the

template for each section of the report.

Discussion Questions

Answer the following questions in the Discussion section of your report. You should consider

these questions as you are performing your experiment. Take enough notes so that you can answer

the questions after you have finished the experiment.

1. Did your solutions in Part I obey Beer’s Law? How do you know?

2. Compare and contrast the features of a primary color spectrum with those of a secondary color spectrum.

3. Without using a spectrometer or any other instrument, how could you estimate the concentration of an unknown dye solution?

4. Would you be able to use your line of best fit Beer’s Law equation obtained in Table 2 of this experiment to calculate an unknown concentration of another primary color

Froot Loop®? Justify your answer.

References:

This experiment was adapted from: Stevens, K. E. J. Chem. Educ. 2006, 83, 1544-1545.

Data Sheet Froot Loops®

Your name ___________________________________________

Lab Partner’s name ___________________________________________

Lab Section ____________________

Table 1: Stock Dye Solution Data

Dye solution Peak (max) wavelength Absorbance

Red

Blue

Yellow

Table 2: Beer’s Law Data Table

Concentration Wavelength from Table 1 Absorbance

0.1

0.2

0.4

0.5

Best-fit line equation

Table 3: Concentration of Extracted Dye

Primary color Wavelength from

Table 1

Absorbance Concentration

Secondary color Wavelength from

Table 1

Absorbance Concentration

Calculations