REDOofSpectroscopy II Lab Report

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University of Akron *

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154

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Chemistry

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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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