# lab 5 procedure.pdf - How much caffeine/benzoic acid is in...

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Chapter 43 / Exercise 3
A Small Scale Approach to Organic Laboratory Techniques
Lampman/Pavia Expert Verified
1 How much caffeine/benzoic acid is in Mountain Dew using simultaneous equationsThe lab is to be done in pairs, but the report is an individual Work Learning Objectives:(i) Be able to read absorbance values at appropriate wavelengths. (ii) Be able to generate a calibration curve, interpret its quality, and use it to quantify an analyte. (iii) Be able to select optimum wavelengths for setting up simultaneous equations. (iv) Be able to predict if a molecule is ultra-violet active or not based on structure. (v) Be able to use simultaneous equations to analyze a binary system. Pre-lab Questions: 1. [2 points] Use of Beer’s law to solve for two components using simultaneous equations is based on [structural properties, proportional relationship, additivity property, chemical equilibrium, ionic strength] of the components in a given sample. 2. [2 points] In quantitative analysis where instruments are used, the signal (e.g. absorbance, pH, voltage) is the response due to [sample, ionic strength, temperature, analyte, blank]. 3. [2 points] Based on the literature search, what are the pKavalues of benzoic acid and protonated caffeine? 4. [2 points] What is the rationale for using a 0.01 M HCl as the solvent for preparing solutions in this lab? 5. [4 points] Solve for X and Y in the following simultaneous equations: 2.25 X + 6.55 Y = 10.65 7.25 X + 4.75 Y = 12.45 Background:Beer-Lambert law states that the log of the ratio of the power of a beam of monochromatic light incident on the sample (Io) over the radiation past the sample (I) is defined as absorbance (A). The absorbance of a solution containing one chromophore is proportional to the concentration of the chromophore, C, the absorptivity, , and the optical path length, b. That is,
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The document you are viewing contains questions related to this textbook. The document you are viewing contains questions related to this textbook.
Chapter 43 / Exercise 3
A Small Scale Approach to Organic Laboratory Techniques
Lampman/Pavia Expert Verified
2 CbIIAolog(1) In equation (1), = molar absorptivity (L/mol.cm), b = path length, (cm), C = concentration (mol/L). The absorptivity, , is dependent on the structure of the compound and changes with the wavelength. The absorbance of a solution that contains more than one chromophore will be equal to the sum of the absorbances of each of the components at any one wavelength. For b = 1.00 cm, A
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