Solutions and Indicators

For the problem given in 7.9, find the next basis. Show the steps you take to calculate the improved solution, and indicate what the basic variables and nonbasic variables are in the new set of equations. (Just a single step from one vertex to the next is asked for in this problem.)... 

The conclusions from IR spectroscopy have been confirmed by recent Raman spectroscopy studies55,56 on the constituent bases of RNA, their nucleosides and nucleotides, and on related model compounds. The Raman spectra of cytosines rule out the prevalence of the imine form 6 in solution and indicate that the neutral molecules have the structure 2. They also indicate that the removal of a proton from the free base leads to an anion of type 9, and that in the cation N-3 is the site of protonation. 

The reasons for this dramatic drop in the rate of reaction on going from the gas phase to aqueous solution have been discussed above. It may be recalled that the difference in the exothermicity of reactions (23) and (26) is as much as 38 kj mol"1. The relatively small effect of the thermochemistry on the rate can be rationalized by invoking the polar effect in the transition state (Russell 1973 Pross et al. 1991 Roberts 1996). Quantum mechanical studies on the solvent effect on the rate of the CH3 plus H202 system can reproduce the dramatic drop upon going from the gas phase to aqueous solutions and indicate that the major reason is the difference between the solvation energies of H202 and H02- in water (Delabie et al. 2000). 

These corrected values for the pKA of HNO (>11) and reduction potential of NO (< —0.7 V) demonstrate that HNO, rather than NO, is the predominant species in neutral solution and indicate that NO cannot be easily converted to NO- by simple outer-sphere electron transfer (Scheme 6), unlike the O2/O2 redox couple. The different potentials and concentrations of NO and O2 in cellular or physiological systems suggest that NO is essentially inert to reduction to NO in mammalian biology. Note that certain processes in bacteria are suggested to have sufficient potentials to reduce NO (165, 166), which may have some importance both to normal bacterial physiology, including nitrification and denitrification, and to antibacterial and pathogenic responses. 

Buffer solutions and indicators Weak polyprotic acids Titration... 

Such expressions as 1 10 or 10% mean that 1 part by volume of a liquid or 1 part by weight of a solid is to be dissolved in a volume of the diluent or solvent sufficient to make the finished solution 10 parts by volume. Directions for the preparation of colorimetric solutions (CS), test solutions (TS), and volumetric solutions (VS), are provided in the section on Solutions and Indicators under General Tests and Assays, following Appendix X. 

Test Solutions See Solutions and Indicators under General Tests and Assays, following Appendix X. 

Water-Soluble Annatto Extracts Transfer 2 mL or 2 g of sample into a 50-mL separatory funnel, and add sufficient 2 N sulfuric acid to make the solution acidic to pH test paper (pH 1 to 2). Dissolve the red precipitate of norbixin by mixing the solution with 50 mL of toluene. Discard the water layer, and wash the toluene phase with water until it no longer gives an acid reaction. Remove any undissolved norbixin by centrifugation or filtration, and dry the solution over anhydrous sodium sulfate. Transfer 3 to 5 mL of the dry solution to the top of an alumina column prepared as described above. Elute the column with toluene, three 10-mL volumes of dry acetone, and 5 mL of Carr-Price Reagent (see Solutions and Indicators) added to the top of the column. The orange-red band of norbixin immediately turns blue-green. 

Any color does not exceed that produced by 1.0 mL of Magnesium Standard Solution (see Solutions and Indicators) in the same volume as that of a control containing 2.5 mL of the sample solution (corresponding to 10 mg of sample) and the quantities of the reagents used in the test. 

A. Pass 100 5 mL of sample, released from the vapor phase of the contents of the container, through a carbon dioxide detector tube (see Detector Tubes under Solutions and Indicators) at the rate specified for the tube. The indicator change extends throughout the entire indicating range of the tube. 

The various detector tubes called for in the respective Tests are listed under Detector Tubes in Solutions and Indicators. 

Assay Dissolve about 1 g of sample, accurately weighed, in a mixture of 150 mL of water and 10 mL of sulfuric acid in a 300-mL flask. Add 1 drop of orthophenanthroline TS, and immediately titrate with 0.1 A ceric sulfate prepared as indicated in Volumetric Solutions under Solutions and Indicators. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1 A ceric sulfate is equivalent to 24.00 mg of Fe(OH2)2 (OOCCH2NH2)2. 

The detector tube called for in one test is described under Solutions and Indicators. 

Note Reduce the sample gas cylinder pressure with a regulator. Measure the sample gas with a gas volume meter downstream from the detector tubes to minimize contamination of or change to the gas samples. The detector tubes called for in certain tests are described under Solutions and Indicators. 

Note The following tests are designed to reflect the quality of Nitrous Oxide in both its vapor and its liquid phases, which are present in previously unopened cylinders. Reduce the sample gas cylinder pressure with a regulator. Withdraw the samples for the tests with the least possible release of sample gas consistent with proper purging of the sample apparatus. Measure the gases with a gas volume meter downstream from the detector tubes to minimize contamination of or change to the samples. The detector tubes called for in certain tests are described at the end of Solutions and Indicators. 

Procedure Transfer 10.0 mL each of the Standard Preparation and the Test Preparation to separate 25-mL volumetric flasks. Add 5.0 mL of Potassium Permanganate and Phosphoric Acid Solution to each, and mix. After 15 min, add 2.0 mL of Oxalic Acid and Sulfuric Acid Solution to each, stir with a glass rod until the solutions are colorless, add 5.0 mL of fuchsin-sulfurous acid TS (see Solutions and Indicators), dilute with water to volume, and mix. After 2 h, using a suitable spectrophotometer, concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 575 nm, using water as the blank. The absorbance of the solution from the Test Preparation is not greater than that from the Standard Preparation. PH Determine as directed under pH Determination, Appendix IIB. 

Iron Add 2 mL of hydrochloric acid to 500 mg of sample, and evaporate to dryness on a steam bath. Dissolve the residue in 2 mL of hydrochloric acid and 20 mL of water, add a few drops of bromine TS, and boil the solution to remove the bromine. Cool, dilute with water to 25 mL, then add 50 mg of ammonium persulfate and 5 mL of ammonium thiocyanate TS. Any red or pink color does not exceed that produced in a control containing 2.5 mL of Iron Standard Solution (25 pig Fe) (see Solutions and Indicators). 

Assay Dissolve about 100 mg of sample, accurately weighed, in 20 mL of water add 40.0 mL of 0.1 N ceric sulfate prepared as directed for Volumetric Solutions under Solutions and Indicators (or use a commercially available solution) mix well and add 2 mL of silver sulfate solution (5 g of Ag2S04 dissolved in 95 mL of concentrated sulfuric acid). Cover, heat nearly to boiling, and continue heating for 30 min. Cool to room temperature, and titrate with 0.1 A ferrous ammonium sulfate to a pale yellow color. Add 2 drops of orthophenanthroline TS, and continue the titration to a salmon-colored endpoint, recording the volume required, in milliliters, as S. Perform a residual blank titration (see General Provisions), and record the volume required as B. Each milliliter of the volume B - S is equivalent to 2.650 mg of NaH2P02H20. 

Standardized Iodine Solution Dissolve about 4.7 g of iodine in a solution of 6 g of iodate-free potassium iodide in 100 mL of water, add 3 drops of hydrochloric acid, and dilute with water to 1000 mL. Standardize to 0.0333 N as directed for 0.1 N Iodine (see Volumetric Solutions under Solutions and Indicators). Adjust the normality repeatedly, if necessary. 

N Sodium Thiosulfate Dissolve 62.5 g of sodium thiosulfate (Na2S203-5H20) in 750 mL of recently boiled and cooled water, add 3.0 mL of 0.2 N sodium hydroxide as a stabilizer, dilute to 1000 mL with water, and mix. Standardize as directed for 0.1 N Sodium Thiosulfate (see Solutions and Indicators), and, if necessary, adjust to exactly 0.250 N. 

The directions given for the preparation of solutions and indicators are for guidance the use of commercially available ones is acceptable. 

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