REDOofSpectroscopy II Lab Report

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Feb 20, 2024

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Moran-1 Spectroscopy II Lab Report Chemistry 154.003 Exp. 3: Spectroscopy II Kaylee Moran February 8, 2024 Partner: Sydney Stacklin TA: Sravya Objective The goal of this experiment is to figure out the concentrations of two species (Nickel, Ni, and Cobalt, Co) present in an unknown solution #282 and both of the species are colored. Experimental Procedure The procedure used was based on that in Semi-Quantitative Experiments for General Chemistry, The University of Akron, Spring 2020 Edition (course lab manual) . Two 25mL burets and two cuvettes were checked out of the stockroom. Both cuvettes were matched using deionized water roughly 2-3 millimeters above the minimum fill mark, keeping the second sample cuvette within 1% above or below the first reference cuvette. 40 mL of both nickel and cobalt and were obtained and the maximum wavelength (λmax) and molarity (M) of both were recorded in the lab notebook. Dilutions were prepared for both nickel and cobalt according to Table 1 and were put into clean, dry, and labeled test tubes and then stirred with a clean, dry stirring rod. Each test tube was poured in turn into the sample cuvette and placed into spectrophotometer at nickel’s λmax and cobalt’s λmax. %T was recorded for each test tube dilution and then converted to absorbance (A). A Beer-Lambert plot ( Figure 1 and Figure 2 ) was crafted for nickel and cobalt (A vs concentration) to determine their respective molar absorptivity ( ε Ni and ε Co ).

Moran-2 The spectrophotometer was changed to nickel’s λmax (390nm) which is λ 1 . Cuvette with pure, undiluted cobalt was placed into spectrophotometer and %T was recorded. The spectrophotometer was changed to cobalt’s λmax (510nm), which is λ 2 . A cuvette with pure, undiluted nickel was placed into spectrophotometer and %T was recorded. The unknown sample #282 was then placed into the sample cuvette and tested in spectrophotometer at 390 nm, resulting in a value of %T. The %T needed to be between 10-90%, so the unknown sample #282 was diluted, which is shown in Table 4 . 20 mL water and 2 mL unknown solution #282 was diluted, stirred, and %T was taken at 390 nm, this time resulting in a %T value of 56.1%T, which was in the accepted range. The diluted #282 sample was taken at 510 nm, resulting in a %T value of 66.0%. Both of these recorded %T values were then converted to A and then used to find the concentration of nickel and cobalt in the undiluted unknown sample #282. Sample Calculations Converting from %T to A: A= 2 – log (%T) For 15mL nickel at 390nm, %T= 32.7% A= 2 – log (32.7) A= 0.4855 Determining the Concentration of a Diluted Standard Sample For 12mL Standard solution sample: M 1 V 1 = M 2 V 2 M 2 = concentration (C) 0.1M × 12mL = M 2 × 15mL M 2 = 0.1M×12mL 15mL M 2 = 0.08

Moran-3 One-Point Determinations To find ε Ni2 : A = 𝛆 𝐥𝐂 0.0048= ε × 1𝑐𝑚 × 0.1 𝛆 = 0.0048 1×0.1 ε Ni2=0.048 Determining Concentration in Unknown Sample For Cobalt in Unknown: C Co = A 1 / ε Ni1 ℓ – A 2 / ε Ni2 ℓ ÷ ε Co1 ℓ / ε Ni1 ℓ - ε Co2 ℓ/ ε Ni2 ℓ C Co = 0.2708/4.7915 – 0.1801/0.048 ÷ 0.250/4.7915 – 5.026/0.048 C Co = -3.695/-104.656 C Co = 0.035311 M For Nickel in Unknown: A 1 = ε Ni1 ℓ C Ni + ε Co1 ℓ C C0 0.2708 = 4.7915 × 1 × C Ni + 0.250 × 1 × 0.035311 0.2708 =4.7915 × C Ni + 0.00882775 0.26197= 4.7915 × C Ni To find ε Co1: A = 𝛆 𝐥𝐂 0.0250= ε × 1𝑐𝑚 × 0.1 ε = 0.0250 1×0.1 ε Co 1=0.250

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Moran-4 C Ni = 0.05467 M Determining Concentration of Unknown in Undiluted Sample ? 1 𝑉 1 = ? 2 𝑉 2 ? 1 × 2𝑚? = 0 .035311? × 22𝑚? ? 1 = 0 .035311? ×22𝑚? 2𝑚? ? 1 = 0.388M Results From the bottle of Nickel Sample: [Ni] = 0.1 M λ 1 =390 nm From the bottle of Cobalt Sample: [Co] = 0.1 M λ 2 =510 nm Table 1 Dilutions for each labeled test tube. These exact dilutions were done for both nickel and cobalt.

Moran-5 Standard Standard (mL) Water (mL) %T A C 390 nm 15.00 0.00 32.7 0.4855 0.1 12.00 3.00 45.2 0.3448 0.08 9.00 6.00 60.8 0.2161 0.06 6.00 9.00 67.4 0.1713 0.04 3.00 12.00 80.7 0.0931 0.02 510 nm 15.00 0.00 98.9 0.0048 0.1 Table 2 %T, A, and C values for Nickel at 390 nm (λ 1) and 510 nm ( λ 2) . Figure 1. Beer ‐ Lambert plot of nickel at its λmax value of 390 nm. The molar absorptivity at 390 nm was determined from the best fit line. From the best fit line of the Beer Lambert plot, the molar absorptivity ( ε Ni ) of nickel at 390 nm was determined to be 4.7915 𝑴 −𝟏 𝒄𝒎 −𝟏 . Standard (mL) Water (mL) %T A C 510 nm 15.00 0.00 32.7 0.4855 0.1 12.00 3.00 50.9 0.2933 0.08 9.00 6.00 61.2 0.2132 0.06 6.00 9.00 78.8 0.1035 0.04 3.00 12.00 83.6 0.0778 0.02 390 nm 15.00 0.00 94.4 0.0250 0.1 Table 3 %T, A, and C values for Cobalt at 390 nm (λ 1) and 510 nm ( λ 2) . y = 4.7915x - 0.0253 R² = 0.9599 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.02 0.04 0.06 0.08 0.1 0.12 Absorbance Concentration (M) Beer-Lambert Plot of Nickel at 390 nm

Moran-6 Figure 2. Beer ‐ Lambert plot of cobalt at its λmax value of 510 nm. The molar absorptivity at 510 nm was determined from the best fit line. From the best fit line of the Beer Lambert plot, the molar absorptivity ( ε Co ) of cobalt at 510 nm was determined to be 5.026 𝑴 −𝟏 𝒄𝒎 −𝟏 . y = 5.026x - 0.0669 R² = 0.9302 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.02 0.04 0.06 0.08 0.1 0.12 Absorbance Concentration (M) Beer-Lambert Plot of Cobalt at 510 nm

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Moran-7 Unknown Sample Unknown #282 UNK #282 Dilution Unknown (mL) V initial 0.00 V final 2.00 V total 2.00 Water (mL) V initial 0.00 V final 20.00 V total 20.00 V diluted unknown (mL) 22.00 %T at 390nm 0.1 53.6 A at 390 nm 3.00 0.2708 %T at 510 nm 66.0 A at 510 nm 0.1805 The concentration of cobalt in unknown #282 was determined to be 0.388M and the concentration of nickel in the unknown #282 was determined to be 0.6014M. Discussion In this experiment, the values of C Co and C Ni were determined for Sample #282. Figure 1 presented the molar absorptivity of Nickel at 390nm, determined to be 4.7915 ? −1 𝑐𝑚 −1 , which is ε Ni1. Figure 2 presented the molar absorptivity of Cobalt at 510nm, determined to be 5.026 ? −1 𝑐𝑚 −1 , which is ε Co2. ε Co1 and ε Ni2 were found using one-point determinations found on page three. ε Co1 was determined to be 0.250 ? −1 𝑐𝑚 −1 and ε Ni2 was determined to be 0.048 ? −1 𝑐𝑚 −1 . Absorptivity of unknown #282 undiluted sample at 390nm was found to be Table 4 The initial, final, and total volumes of water and UNK #282 for the dilution, as well as the %T and A value for each solution. The dilution yielded a usable %T value.

Moran-8 0.2708, which is A 1 . Absorptivity of unknown #282 undiluted sample at 510nm was found to be 0.1801, which is A 2 . Sample #282’s C Co was found to be 0.0353M by using ε Co1, ε Co2, ε Ni1, ε Ni2, A 1, and A 2 values previously stated. The resulting value of 0.0353M was then used to find the concentration of nickel (C Ni ) in the unknown #282 sample, resulting in a value of 0.05467M. C Co and C Ni values were then used to determine the concentration of Cobalt and Nickel in the unknown undiluted sample by using the formula of ? 1 𝑉 1 = ? 2 𝑉 2 . M 1 of Cobalt was solved for by using 2mL for V 1 , M 2 was C co value of 0.0353, and 22mL for V 2 , resulting in a concentration of 0.388M. M 1 of Nickel was solved for by using 2mL for V 1 , M 2 was C Ni value of 0.05467, and 22mL for V 2 , resulting in a concentration of 0.6014M. Therefore, the concentration of cobalt in the unknown #282 undiluted sample was determined to be 0.388M and the concentration of nickel was determined to be 0.6014M. Several sources of error could have influenced this experiment to varying extents. Achieving complete drying of the cuvettes after water rinsing posed a significant challenge. The residual water in the cuvettes could potentially dilute any subsequently added samples, resulting in elevated %T values and reduced A values. If such dilution occurred during the unknown sample's preparation, the experimental A value and concentration might register as lower than the actual values. Despite efforts to rinse cuvettes with the measured solution, this phenomenon could still exert an impact, ultimately leading to incorrect concentration values in the unknown. Additionally, the presence of scratches, smudges, or internal dust within the cuvette was a plausible source of error. In these scenarios, the introduction of extra solids or imperfections in the glass could scatter the initial radiation before reaching the solution in the cuvette. Consequently, the amount of transmitted radiation might be diminished, leading to higher A values and consequently, higher concentrations.