Ultraviolet-Visible Spectrophotometry Worksheet with Answers PDF

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Problems in UV-Vis Spectroscopy: A 0-g sample of insulation was analyzed for formaldehyde residue by extraction with 25 mL of extracting solution. After extraction, the sample was filtered and the filtrate analyzed without further dilution. The concentration of formaldehyde in this extract was deter...

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Problems in UV-Vis Spectroscopy: 1. A 0.5693-g sample of insulation was analyzed for formaldehyde residue by extraction with 25.00 mL of extracting solution. After extraction, the sample was filtered and the filtrate analyzed without further dilution. The concentration of formaldehyde in this extract was determined to be 4.20 ppm. What is the concentration of formaldehyde in the insulation?

2. A water sample was tested for iron content, but was diluted prior to obtaining the instrument reading. The dilution involved taking 10 mL of the sample and dilution it to 100 mL. If the instrument reading gave a concentration of 0.891 ppm, for this diluted sample, what is the concentration in the diluted sample?

3. A 2.000-g soil sample was analyzed for potassium content by extracting the potassium using 10.00 mL of aqueous ammonium acetate solution. The soil was rinsed and the solution diluted to exactly 50.00 mL. Then, 1.00 mL of this solution was diluted to 25 mL and measured with an instrument. The concentration in this 25 mL was found to be 3.18 ppm. What is the concentration of the potassium in the soil in ppm?

4. A sample is analyzed to determine the concentration of an analyte. Under the conditions of the analysis the sensitivity is 17.2 ppm–1. What is the analyte’s concentration if S total is 35.2 and Sreag is 0.6?

For numbers 5-9: An analyst needs to evaluate the potential effect of an interferent, I, on the quantitative analysis for an analyte, A. She begins by measuring the signal for a sample in which the interferent is absent and the analyte is present with a concentration of 15 ppm, obtaining an average signal of 23.3 (arbitrary units). When she analyzes a sample in which the analyte is absent and the interferent is present with a concentration of 25 ppm, she obtains an average signal of 13.7. 5. What is the sensitivity for the analyte?

6. What is the sensitivity for the interferent?

7. What is the value of the selectivity coefficient?

8. Is the method more selective for the analyte or the interferent?

9. What is the maximum concentration of interferent relative to that of the analyte if the error in the analysis is to be less than 1%?

For numbers 10-13: Ibrahim and co-workers developed a new method for the quantitative analysis of hypoxanthine, a natural compound of some nucleic acids.14 As part of their study they evaluated the method’s selectivity for hypoxanthine in the presence of several possible interferents, including ascorbic acid. 10. When analyzing a solution of 1.12×10–6 M hypoxanthine the authors obtained a signal of 7.45×10–5 amps. What is the sensitivity for hypoxanthine? You may assume the signal has been corrected for the method blank.

11. When a solution containing 1.12×10–6 M hypoxanthine and 6.5×10–5 M ascorbic acid is analyzed a signal of 4.04×10 –5 amps is obtained. What is the selectivity coefficient for this method?

12. Is the method more selective for hypoxanthine or for ascorbic acid?

13. What is the largest concentration of ascorbic acid that may be present if a concentration of 1.12×10–6 M hypoxanthine is to be determined within 1.0%?

For 14-16 The Wien displacement law states that the wavelength maximum in micrometers for blackbody radiation is

where T is the temperature in kelvins. 14. Calculate the wave- length maximum for a blackbody that has been heated to *(a) 4000 K, (b) 3000 K, *(c) 2000 K, and (d) 1000 K.

15. Calculate the wavelength of maximum emission of a tungsten-filament bulb operated at 2870 K and at 3000 K.

16. Calculate the total energy output of the bulb in W/cm2.

or 17 – 20 A portable photometer with a linear response to radiation registered a photocurrent of 75.9 𝜇A with a blank solution in the light path. Replacement of the blank with an absorbing solution yielded a response of 23.5 𝜇A. Calculate 17. The percent transmittance of the sample solution

18. The absorbance of the sample solution

19. The transmittance to be expected for a solution in which the concentration of the absorber is one third that of the original sample solution.

20. The transmittance to be expected for a solution that has twice the concentration of the sample solution....