Aqueous solutions identifying ions

Elemental composition K 39.85%, C 24.48%, H 3.08%, 0 32.60%. Potassium may be identified by flame testing. An aqueous solution can be analyzed for potassium by flame photometry, ICP/AES, or ion selective electrode (see Potassium). Acetate anion may be measured in aqueous solution by ion chromatography under appropriate conditions. 

Water of crystallization may be measured by thermogravimetry. Zirconium may be analyzed in an aqueous solution by flame AA or ICP-AES. Sulfate may be identified in an aqueous solution by ion chromatography or by precipitation with barium chloride. 

Selva and coworkers - reported on their experiences to apply various mass spectrometric techniques to the analysis of -carotene and carotenoids and their adducts formed in aqueous solution. El mass spectrometry and field desorption (FD) mass spectrometry were applied to aqueous mixtures of -carotene and /J-cyclodextrin, and the polyene was found to be detectable . Tandem mass spectrometry can be applied to identify fi-carotenone as a minor component in complex carotenoid mixtures. EI/MIKE spectrometry of the molecular ion m/z 600) was used in this case . A previous study was focused on the characterization of. vecw-carotcnoids using EI/MIKE and CID spectrometiy . The more recent ionization methods, viz. MALDI and its variant working without a matrix, laser desorption/ionization (EDI), as well as electrospray ionization (ESI) mass spectrometry, have also been applied to this topic. MALDI and LDI mass spectrometry were used to analyse mixtures of -carotene and y-cyclodextrin in aqueous solution. Adduct ions were not observed using these mctbods. ... 

On the basis of the nucleophilicity parameters B, NBs, and fi (see Table 8-2) one expects less of the homolytic product in water than in methanol. This is, however, not the case. It has been known for many decades that a very complex mixture of products is formed in the decomposition of diazonium ions, including polymeric products, the so-called diazo tars. In alcohols this is quite different. The number of products exceeds three or four only in exceptional cases, diazo tars are hardly formed. For dediazoniation in weakly alkaline aqueous solutions, there has, to the best of our knowledge, been only one detailed study (Besse et al., 1981) on the products of decomposition of 4-chlorobenzenediazonium fluoroborate in aqueous HCOf/ CO]- buffers at pH 9.00-10.30. Depending on reaction conditions, up to ten compounds of low molecular mass were identified besides the diazo tar. 

Write the proton transfer equilibria for the following acids in aqueous solution and identify the conjugate acid-base pairs in each one (a) H2S04 (b) C6H5NH3+. anilinium ion ... 

Identify the nature of each solute. If it is a salt, strong acid, or strong base, it generates ions in aqueous solution. All other solutes give aqueous solutions that contain molecules as the major species. 

The first step In balancing a redox reaction is to divide the unbalanced equation into half-reactions. Identify the participants in each half-reaction by noting that each half-reaction must be balanced. That Is, each element In each half-reaction must be conserved. Consequently, any element that appears as a reactant In a half-reaction must also appear among the products. Hydrogen and oxygen frequently appear in both half-reactions, but other elements usually appear In just one of the half-reactions. Water, hydronium ions, and hydroxide ions often play roles In the overall stoichiometry of redox reactions occurring in aqueous solution. Chemists frequently omit these species in preliminary descriptions of such redox reactions. 

The molecular structure of Li-, Na-, and K-silicates in 0.2 to 3 mole SiOj/L aqueous solutions has been investigated by FTIR and Raman spectroscopy to help exploring their solidification process. These silicates were found to be only partially dissociated and their average molecular weight (AMW) varies with the type of the alkaline ion, the alkaline/silicon ratio, and the concentration. It is demonstrated that these differences are associated with differences in the Qn connectivity ratios of [Si04] tetrahedra and in the dominating siloxane ring structures which can be identified by their vibrational spectra. 

Numerous investigations have shown the existence of the heptamolybdate, [Mo7024]6 , and octamolybdate, [Mo8026]4, ions in aqueous solution. Potentiometric measurements with computer treatment of the data proved to be one of the best methods to obtain information about these equilibria. Stability constants are calculated for all species in a particular reaction model, which is supposed to give the best fit between calculated and experimental points. In the calculations the species are identified in terms of their stoichiometric coefficients as described by the following general equation for the various equilibria... 

The ions with six metal atoms have the same structure as the hexa-molybdate ion [Mo6Oi9]2 . The [Mo5VOi9]3 ion, previously identified in acetonitrile medium (166) can be obtained in the solid state by precipitation from an aqueous solution with tetramethyl ammonium as cation (165). The vanadium atoms in both [Mo4V2Oi9]4 and its pro-tonated form [HMo4V2Oi9]3 (pKa = 3.8) are in cis positions. Protonation seems to take place at the oxygen, which bridges the two vanadium atoms. 

On the other hand, new solution species are being identified. For example, some polynuclear species and some ion pair complexes are now recognized as being more significant in aqueous solutions than previously thought. There is therefore a need to develop, extend and up-date the data on new species which come to be recognized as significant. 

The different molecular species present in a palladium nitrate solution can be easily identified by UV-visible spectroscopy (Fig. 13.2). Two absorption peaks are generally observed at A, = 285 nm and A = 378 nm, the latter being ascribed to free nitrate ions corresponding to the electronic transition from the a to the it state in the NOs ions, as observed in the case of an aqueous solution of NaNOs. The other absorption band at A = 285 nm is assigned to a d-d transition in the aquo complex Pd(H20)4 These UV-visible results show the noncomplexant behavior of nitrate ions toward palladium metallic centers. The palladium containing species in the starting solution is then the planar tetra-aquo complex Pd(H20)4 +. 

The scheme that is shown in Figure 9.9 is very simple. More complex qualitative analyses involve many more steps of isolation and identification, including some steps that are not precipitation reactions. For example, some ions, such as sodium, Na", and potassium, K, cannot he precipitated out of an aqueous solution, because the ionic compounds that contain them are always soluble. Instead, chemists identify these ions using a flame test. In the following ThoughtLab, you will simulate a qualitative analysis that includes a flame test. 

Chemical/Physical. The aqueous chlorination of biphenyl at 40 °C at a pH range of 6.2 to 9.0 yielded 2-chlorobiphenyl and 3-chlorobiphenyl (Snider and Alley, 1979). In an acidic aqueous solution (pH 4.5) containing bromide ions and a chlorinating agent (sodium hypochlorite), 4-bromobiphenyl formed as the major product. Minor products identified include 2-bromobiphenyl, 2,4- and 4,4 -dibromobiphenyl (Lin et al., 1984). 

When an aqueous solution containing chlorobenzene (190 pM) and a nonionic surfactant micelle (Brij 58, a polyoxyethylene cetyl ether) was illuminated by a photoreactor equipped with 253.7-nm monochromatic UV lamps, phenol, hydrogen, and chloride ions formed as major products. It was reported that aromatic aldehydes, organic acids, and carbon dioxide would form from the photoreaction of chlorobenzene in water under similar conditions. A duplicate experiment was conducted using an ionic micelle (triethylamine, 5 mM), which serves as a hydrogen source. Products identified were phenol and benzene (Chu and Jafvert, 1994). 

Chemical/Physical. Matheson and Tratnyek (1994) studied the reaction of fine-grained iron metal in an anaerobic aqueous solution (15 °C) containing chloroform (107 pM). Initially, chloroform underwent rapid dehydrochlorination forming methylene chloride and chloride ions. As the concentration of methylene chloride increased, the rate of reaction appeared to decrease. After 140 h, no additional products were identified. The authors reported that reductive dehalogenation of chloroform and other chlorinated hydrocarbons used in this study appears to take place in conjunction with the oxidative dissolution or corrosion of the iron metal through a diffusion-limited surface reaction. 

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