Chem 218 Exp 2

It was also important to use deionized water to rinse

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solvent may just settle at the bottom. It was also important to use deionized water to rinse the lab material before use to not contaminate the material with materials used in past labs as well as to rinse the material with deionized water to ensure that all solution is added to the flasks. There were several error sources in this lab. Because we had 0.05 M Iron (III) chloride and not 0.005M, it was more concentrated, so we needed only 60 mL of it adding deionized water to it until it reached 600mL. Also, the Spec 20 was difficult to use at first because of out inexperience with the device and therefore are not very confident on our readings of the device and the %T numbers that were calculated. In this lab, we found that transmittance goes down as wavelength increases.

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Questions 1. Calculate the concentrations of both stock solutions. Concentration of SA in volumetric flask A (0.29g/138.12g/mol)/250 mL x100=0.000839849 mol/L Concentration of SA in volumetric flask B (0.000839849 mol/L) x 0.050L = 0.000041992 mol/.250L = 0.00016797mol/L 2. Calculate the concentration of the 5 standard solutions and report those concentrations in a table with the absorbance measured. Standard Solution 1: M1V1=M2V2 (0.000168)(0.025)=M2(0.1) M=4.2 x 10¯ Standard solution 2: M=3.36 x 10¯ Standard Solution 3: M= 2.52 x 10¯ Standard Solution 4: M= 1.68 x 10¯ Standard Solution 5: M= 8.4 x 10¯ 3. Using Excel, create an absorbance spectrum (absorbance vs. wavelength) and a Beer’s Law Plot (absorbance vs. concentration). 4. Using the Beer’s Law Plot, find the concentration of ASA in your unknown cuvette graphically and mathematically. Graphically the concentration of the unknown would be about 0.0002M. Mathematically the concentration would be: 5.6 x 10 -5 M. 5. Using the data from your Beer’s Law Plot, what is the value of the molar extinction coefficient (also called the molar absorptivity coefficient) for the Iron (III) -Acetylsalicylic acid ion)? (The diameter of the cuvette is 1.30 cm.) E= a/bc
E= (0.122) / (1.30cm) (5.6 x 10 -5 M) = 1675.8L/mol.cm 6. Using the data from your Beer’s Law Plot, calculate a. The exact mass in grams and of ASA in your aspirin unknown b. The mass percent of ASA in your aspirin unknown (5.6 x 10 -5 M ) (180.16g/mol) = 0.0101 g/L (0.0101 g/L) (.25L) = .2.5 x 10 -4 g
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• Fall '12
• professoridon'tknow
• Salicylic acid, standard solution

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