# Spectroscopy Homework Problem Set #2c

This problem set was developed by S.E. Van Bramer for Chemistry 366 at Widener University.

Questions are based on Skoog, West & Holler An Introduction to Analytical Chemistry. Some questions and data are based upon information from this textbook.

1. What is the wavelength of the maxium emission for a blackbody radiator at 2800 K? At 3500 K? What type of source can operate at this temperature? If the bulb has a filliment that is 10 inches long with a radius of 0.05 mm, what is the total energy output?

2. Compare and contrast the following instrument components. (This means, discuss the advantages and disadvantages of each in YOUR own words. DO NOT explain how they work.):
1. Hydrogen discharge and deuterium discharge lamps
2. dispersive and diode array spectrometers
3. photodiode and photomultiplier
4. filter and monochrometer

3. Compounds A and B have the following molar absorbtivities. Graph the absorption spectrum for a solution that is :
1. 6.78 x 10-4M in A with a 1.00 cm cell.
2. 5.43 x 10-4M in B with a 1.00 cm cell.
3. 6.78 x 10-4M in A and 5.43 x 10-4M in B and with a 1.00 cm cell.
4. If a solution has an absorbance of 0.360 at 540 nm in a 1.00 cm cell, what is the concentration of B if the concentration of A is 5.00 x 10-4M?

 Wavelength (nm) A (M-1 cm-1) B (M-1 cm-1) 400 893 0 420 940 0 440 955 0 460 936 24.6 480 874 102 500 795 185 520 691 289 540 574 428 560 440 622 580 297 980 600 167 1178 620 39.7 1692 640 3.45 1742 660 0 1806 680 0 1809 700 0 1757

4. A pH indicator has a different molar absorbtivity at 450 nm for the two different forms. When the pH is 1, a 8.00x10-5M solution of the indicator has an absorbance of 0.758 in a 1.00 cm cell. When the pH is 13, this same solution has an absorbance of 0.076 in a 1.00 cm cell. if pKa = 4.92 for this indicator, what is the absorbance when the pH is 4.92? Clearly state any simplifying assumptions that you make.

5. Phenanthrene is a highly fluorescent PAH (Polycyclic aromatic hydrocarbon) with an excitation maximum at 250 nm and an emission maximum at 370 nm. Results for a set of standards are given below.
1. Construct a calibration curve for Phenanthrene
2. Calculate the slope and intercept for the linear regression
3. Calculate the standard deviation of the slope, the standard deviation of the intercept, and the standard deviation about the regression.
4. Calculate the concentration of an unknown with a signal of 2.1562.
5. Calculate the relative standard deviation for the concentration of the unknown.
6. Calculate the relative standard deviation for the concentration of the unknown if it is the average of 4 measurements.

 Concentration Intensity 0.000 0.0558 0.100 0.4755 0.200 1.0089 0.300 1.6262 0.400 1.9294 0.500 2.5002 0.600 3.1108 0.700 3.5893 0.800 3.7099 0.900 4.2843 1.000 5.0206

Please send comments or suggestions to svanbram@science.widener.edu

Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013