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Chapter 18: Q6TY (page 443)
Describe a different set of dilutions to produce 3 mg Fe/mL from 1 000 mg
Fe/mL
Dilute 10 mL of stock to 100 mL to get. Dilute of the new solution up to 100 mL to get
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Calculate the frequency (Hz), wavelength, and energy (J/photon and J/mols of photon]) of visible light with a wavelength of 562 nm.
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.
Nitrite ion, is a preservative for bacon and other foods, but it is potentially carcinogenic. A spectrophotometric determination ofmakes use of the following reactions
Here is an abbreviated procedure for the
determination:
1. To 50.0ml of unknown solution containing nitrite is added 1.00mL of sulfanilic acid solution.
2. After 10min , 2.00mL of 1 –a minonaphthalene solution and 1.00 mL of buffer are added.
3. After 15 min, the absorbance is read at 520 nm in a 5.00-cm cell.
The following solutions were analyzed:
A. 50.0 mL of food extract known to contain no nitrite (that is, a negligible amount); final absorbance =0.153.
B. 50.0mL of food extract suspected of containing nitrite; final absorbance \(=0.622\).
C. Same as B, but with added to the 50.0-mL sample; final absorbance =0.967.
(a) Calculate the molar absorptivity, of the colored product. Remember that a \(5.00\)-cm cell was used.
(b) How many micrograms ofwere present in 50.0mL of food extract?
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.
18-27. The iron-binding site of transferrin in Figure 18-8 can accommodate certain other metal ions besides Fe and certain other anions besidesData are given in the table for the titration of transferrin ( 3.57 mg in 2.00 mL ) with 6.64 mM solution in the presence of the anion oxalate, , and in the absence of a suitable anion. Prepare a graph similar to Figure 18-11, showing both sets of data. Indicate the theoretical equivalence point for the binding of one and two ions per molecule of protein and the observed end point. How many ions are bound to transferrin in the presence and in the absence of oxalate?
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