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Chapter 18: Q35P (page 459)
Consider a molecule that can fluoresce from the S1 state and phosphoresce from the T1 state. Which is emitted at longer wavelength, fluorescence or phosphorescence? Make a sketch showing absorption, fluorescence, and phosphorescence on a single spectrum.
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Ammonia can be determined spectrophotometrically by reaction with phenol in the presence of hypochlorite
A 4.37 - mgsample of protein was chemically digested to convert its nitrogen into ammonia and then diluted to 100.0mL. Thenof the solution were placed in a 50 - mLvolumetric flask and treated with 5mLof phenol solution plus 2mLof sodium hypochlorite solution. The sample was diluted to 50.0mLand the absorbance at 625nmwas measured in a 1.00 - cmcuvet after 30min. For reference, a standard solution was prepared from 0.0100g of dissolved in 1.00Lof water. Then 10.0mLof this standard were placed in a50 - mL volumetric flask and analyzed in the same manner as the unknown. A reagent blank was prepared by using distilled water in place of unknown.
(a)Calculate the molar absorptivity of the blue product.
(b)Calculate the weight percent of nitrogen in the protein.
Semi-xylenol orange is a yellow compound at pH 5.9but turns red when it reacts with . A 2.025 - mLsample of semixylenol orange at pH 5.9was titrated withwith the following results:
Total role="math" localid="1663647483742" added | Absorbance at 490nmwavelength | Total added | Absorbance at490nmwavelength |
0.0 6.0 12.0 18.0 24.0 30.0 36.0 | 0.227 0.256 0.286 0.316 0.345 0.370 0.399 | 42.0 48.0 54.0 60.0 70.0 80.0 | 0.425 0.445 0.448 0.449 0.450 0.447 |
Make a graph of absorbance versus microliters of added. Be sure to correct the absorbances for dilution. Corrected absorbance is what would be observed if the volume were not changed from its initial value of 2.025Ml. Assuming that the reaction of semi orange with has a 1 : 1stoichiometry, find the molarity of semi-xylenol orange in the original solution.
Dilution by mass is more accurate than dilution by volume. A stocksolution contains 1.044 g Fe/kg solution in 0.48 M HCl. How many solution are in a solution made by mixing 2.145 g stock solution with 243.27 g 0.1 M HCl?
A compound with molecular mass 292.16g/molwas dissolved in a 5 - mLvolumetric flask. A1.00 - mLaliquot was withdrawn, placed in a 10 - mLvolumetric flask, and diluted to the mark. The absorbance atwas in 0.427 i acuvet. The molar absorptivity at 340nm is
(a) Calculate the concentration of compound in the cuvet.
(b) What was the concentration of compound in the 5 - mL flask?
(c) How many milligrams of compound were used to make the 5 - mLsolution?
Standard addition. Selenium from 0.108 g of Brazil nuts was converted into the fluorescent product in Reaction 18-15, and extracted into 10.0 mL of cyclohexane. Then 2.00 mL of the cyclohexane solution were placed in a cuvet for fluorescence measurement. Standard additions of fluorescent product containingSe/mL are given in the table. Construct a standard addition graph to find the concentration of Se in the 2.00-mL unknown solution. Find the wt%of Se in the nuts and its uncertainty and 95% confidence interval
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