Chem 1141 lab 4 - Lab 4 PDF

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Lab 4...

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Tiara Miller CUNY Queens College; Spring 2020 Professor Edward Look Chemistry 114.1 Sec:6 2/29/2020

Abstract The purpose of this lab was to analyze the various substances in the mixture of unknown black ink. Doing this required analyzing and observing each individual ink separately. Paper chromatography was used in order to separate the ink into its several colors; red, yellow, and blue. The Rf value was calculated for each ink as follows: yellow was 0.41, red was 0.22, and blue was 0.60. Additionally, the λ max was recorded for each ink as follows: yellow was 421.5 nm, red was 527.7 nm, and blue was 625.7 nm. Data from other students with various unknown ink mixtures was compared with my results in order to analyze the characteristics that help identify the individual inks.

Introduction Visible light spectroscopy can be used in order to determine the contents of an unknown colored solution. This is possible since the λ max for each substance is unique and constant, as it indicates the wavelength that the substance experiences peak absorbency. The λ max of each ink in the black ink mixture can be calculated first by separating the inks. In order to separate the inks, paper chromatography must be executed. Paper chromatography consists of two phases, the mobile phase and the stationary phase. The stationary phase is the chromatography paper, as it does not move (thus remaining stationary). The mobile phase is the solvent, in this case 0.10M NaCl, which rises through the paper and the ink travels along with it (thus being mobile). The ink separates into several colors depending on the nature of the ink, as some ink is more attracted to the solvent than other inks, thus causing them to travel in various distances. What was once a single black line has now become bands of several colors, in this case red, yellow and blue. The Rf value of each substance can be calculated with the following formula: Rf = Substance distance / solvent distance ≤ 1. Finding the Rf alongside the λ max can be used in order to identify the substance. The Rf value is a constant ratio, so it is independent of the distance the solvent could travel, as well as the amount of substance applied to the paper.

Procedure

1. First, a 600mL beaker was rinsed with tap water and dried. 2. A precut sheet of chromatography paper was obtained, alongside a small filter paper. 3. Then, the chromatography paper was held in “landscape” orientation and a line was drawn about 1 cm up from the bottom of the paper in PENCIL. I wrote my name as well. 4. Next, an assigned unknown marker was obtained and used to draw a line exactly on the pencil line. The letter on the marker was recorded (In this case- B). 5. Then, the marker was also used to draw a circle about 0.5 cm in diameter on the filter paper. This was put aside for later. 6. Next, the chromatography was rolled into a cylinder (with the line outside) and the edges of the paper were stapled together, leaving a gap between the edges. 7. Then, about 1 cm of 0.10M NaCl mobile phase solution was poured into the beaker. The level of the mobile phase was lower than the ink line on the paper. 8. Next, the cylinder was carefully lowered into the center of the beaker. The beaker was covered with a watch glass and put aside. The mobile phase was left alone until it reached about 1 cm from the top of the paper. 9. Then, while the mobile phase started to rise, the filter paper from Step 5 was obtained. The ink circle was torn out and placed in a 50mL beaker. 10. Next, 3mL of mobile phase was added to the beaker and swirled. This beaker was put to sit for a few minutes, while swirling occasionally. The liquid became dark. 11. Then, the dark liquid was poured into a test tube and saved for spectral analysis later. 12. Next, the mobile phase reached its desire distance, the paper was removed from the beaker. Excess liquid was blotted, and the solvent distance was marked with a pencil. The cylinder was placed in a drying oven. 13. Once the paper dried, the stapled edges were pulled apart, so the paper laid flat. The different color bands were present on the paper. 14. Then, a 3cm wide strip was cut from the paper to measure the Rf values of each ink. The distance of the solvent traveled was measured from the start line to the pencil-marked line from Step 12, and the distance of each ink was measured from the start line to the center of each colored band. These values were used to calculate the Rf values. 15. Next, using the rest of the chromatography paper, the colored bands were individually cut out and further cut into smaller pieces, this was done carefully to prevent including color overlaps in the strips. 16. Then, each ink strip was placed in individual small beakers, and 3mL of the mobile phase was added to each using a graduated cylinder. The beakers were swirled, and left to sit,

swirling occasionally. The goal of this step was to extract as much of the ink from the paper into the liquid mobile phase solution. 17. Next, each colored extract was poured into individual test tubes and put aside for spectral analysis. 18. Then, a LabQuest device, alongside a spectrometer, was obtained in order to determine the λ max of each extract. The spectrometer was calibrated with distilled water prior to spectral analysis. 19. Next, the black ink extract was poured into the cuvette and the spectrum was obtained, and the run was renamed “Black Ink”. The ink extract was poured back into the test tube and the cuvette was rinsed. 20. Then, step 19 was repeated for all the ink extracts, labeling each run after the color of ink. The “Store” option was chosen at the beginning of each run. The peak of each spectrum is the λ max value. λ max was also found by selecting “Statistics” from the “Analyze” menu and the “Abs” option was selected. The largest value was noted as λmax. 21. Then, the spectra for all the extracts was obtained, “File” was selected and “Save” was clicked. The file was named and exported as a text file to a USB drive. 22. Finally, all materials were then properly washed, rinsed, dried, and put away. The LabQuest was returned to the stockroom neatly for the next student. Data Table 1: Assigned Marker D Analysis Color Yellow Red Blue

Rf 0.28 - 0.41 0.22 - 0.48 0.60 - 0.94

λmax (nm) 390.8 – 421.5 394.1 – 527.7 426.1 – 625.7

Table 2: Marker A Analysis Color Yellow Red Blue

Rf 0.40 - 0.48 0.20 – 0.29 0.77 – 0.93

λmax (nm) 413.8 – 579.2 535.4 – 617.6 581.5 – 627.9

Table 3: Marker B Analysis Color Yellow Red Blue

Rf 0.45 – 0.51 0.66 0.85 – 0.92

λmax (nm) 443.6 – 563.7 414.0 – 498.2 410.5 – 624.2

Table 4: Marker C Analysis Color Yellow Red Blue

Rf 0.42 – 0.47 0.60 – 0.62 0.84 – 0.86

λmax (nm) 393.8 – 427.3 398.0 – 508.4 439.7 – 629.4

Table 5: Marker E Analysis Color Yellow Red Blue

Rf 0.43 – 0.45 0.24 – 0.77 0.90 – 0.91

λmax (nm) 396.7 – 427.3 533.2 – 559.4 628.3 – 629.4

Calculations/ Results

Calculations: Rf = Substance Distance / Solvent Distance Rf (yellow ink) = 3.3 / 8.1 Rf (yellow ink) = .407  0.41

Rf (red ink) = 1.8 / 8.1 Rf (red ink) = .222  0.22

Rf (blue ink) = 4.9 / 8.1 Rf (blue ink) = .604  0.60

Chart A.

YELLOW 0.1 0.08

Absorbance

0.06 0.04 0.02 0 350 -0.02

450

550

650

750

850

950

-0.04 -0.06 -0.08

Wavelength (nm)

Chart B.

RED 0 350

450

550

650

Absorbance

-0.02 -0.04 -0.06 -0.08 -0.1 -0.12

Wavelength (nm)

750

850

950

Chart C.

BLUE 0.8 0.7

Absorbance

0.6 0.5 0.4 0.3 0.2 0.1 0 350 -0.1

450

550

650

750

850

950

-0.2

Wavelength (nm)

Chart D.

BLACK 1.2 1

Absorbance

0.8 0.6 0.4 0.2 0 350 -0.2

450

550

650

Wavelength (nm)

750

850

950

Discussion The data that the team was able to compare between assigned marker D had shown that the Rf values spanned from 0.28 – 0.41 and the λ max spanned from 390.8 – 421.5nm. The reason for the difference in Rf values and λ max values can be attributed to the likely possibility of procedural error. The Rf values more specifically differed most likely due to the of measurement error with the ruler in several steps, including the pencil line at the bottom and measuring the distance of each ink. The range of values of λ max can be explained more in depth by another form of procedural error while cutting the bands out and while extracting the ink from the chromatography paper. If a color band was not a solid color, for example: yellow ink, seeping into blue ink to make a smaller green band, then this could change the wavelength maximum value. Also, the time allowed for the ink to be extracted from the paper into the mobile phase solution, 0.10M NaCl, was not standardized so some inks may not have been fully extracted into solution. This will also affect wavelength maximum values. In the instance of analyzing and observing two different blue inks that have similar λ max range values but, drastically different Rf values, the two inks could not be the same substance. The reasoning to explain this lies in the importance of the rate that the inks spread. If the R f values are different, this indicates that the inks stopped traveling at different distances and different rates, which would mean that the two substances would not be the same. There were no observations made regarding any pens that contained the same substances in the assigned marker D results. In the case that another pen contained exactly the same inks as the pen that the team analyzed (Marker D), the rate of the movement of the substances should be calculated because if it is the same substance then it will travel at the same rate and will produce an identical Rf.

Conclusion The main focus and purpose of this lab was to separate the components of an unknown black ink and observe the characteristics of each assigned ink. The wavelength maximum was determined for each ink extract through the process of visible spectroscopy. The yellow ink was 421.5 nm, the red was 527.7 nm, and the blue was 625.7 nm. The R f values of each ink extract were calculated by dividing the distance the substance traveled by the distance the solvent traveled (mobile phase). The Rf value was calculated for each ink and the results were that the yellow was 0.41, the red was 0.22, and the blue was 0.60. The rate in which the solute (ink) travels, alongside the distance it traveled, and the wavelength maximum can all be used collectively to identify the substance....