Midterm 2004 - CHEM*3440 Instrumental Analysis Mid-Term...

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CHEM*3440 Instrumental Analysis Mid-Term Examination Fall 2004 Duration: 2 hours [Pd] ppm 0 80 205 325 Instrument Signal 14.1 27.7 48.4 68.6 1. (10 points) An atomic absorption experiment found the following results for a series of standard solutions for dissolved palladium metal ion. The data were plotted in Excel and from the LINEST function, the following values of the parameters were obtained: m = 0.1674 b = 14.17 s m = 0.00051 s b = 0.101 s r = 0.1267 (a) Determine the concentration (in ppm) of an unknown Pd sample whose average signal was 56.5. (b) Calculate the standard deviation of this result, given that the above average was the result of 5 measurements. (c) What is the 95% confidence interval for this result? 2. (10 points) The following data arose out of a determination of Cr in water. The protocol specified to run a blank, the sample and the sample with a series of added standards. Assume that the added standards did not substantively affect the solution volume. Using a graphical approach, calculate the concentration of Cr in the unknown sample. Solution Blank Unknown Addition 1 Addition 2 Addition 3 Added Cr (ppm) 0.000 0.000 2.000 4.000 6.000 Run #1 0.005 0.537 0.666 0.790 0.912 Run #2 0.009 0.548 0.659 0.784 0.901 Run #3 0.006 0.531 0.667 0.805 0.935 3. (5 points) A signal is sampled at a frequency of 15.000 kHz. The signal actually consists of three sinusoidal signals at 6.301 kHz, 11.244 kHz, and 32.863 kHz. If no filtering is applied, at what frequencies would the signals appear due to signal aliasing? 4. (7 points) Below is a voltage divider network used in a photomultiplier tube. The resistors shown give an increasingly large potential step to the next dynode in the chain, assuring that the large volume of electrons are successfully accelerated to it. Calculate the potential at each step (B - H) as indicated, given that the potential at step A is that of the potential source: -1000 V. A B C D E F G H 1k Ω 2k Ω 3k Ω 4k Ω 5k Ω 6k Ω 7k Ω 8k Ω 1000 V
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6. (8 points) A photometer with a linear response to light gave a reading of 685 mV with a blank in the light path and 179 mV when the blank was replaced by an absorbing solution. Calculate (a) the percent transmittance of the sample solution. (b) the absorbance of the sample solution. (c) the percent transmittance expected if the solution concentration was 1/2 of the original concentration. (d) the signal (in mV) expected if the light path were doubled. 7. (9 points) Explain and relate the following collection of terms: (a) Reactance, resistance, and impedance.
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Midterm 2004 - CHEM*3440 Instrumental Analysis Mid-Term...

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