Stoichiometry aqueous solutions

A study of the kinetics of a chemical reaction begins with the measurement of its reaction rate. Consider, for example, the general reaction shown in the following equation, involving the aqueous solutes A, B, C, and D, with stoichiometries of a, b, c, and d. 

At present about 77% of the industrial hydrogen produced is from petrochemicals, 18% from coal, 4% by electrolysis of aqueous solutions and at most 1% from other sources. Thus, hydrogen is produced as a byproduct of the brine electrolysis process for the manufacture of chlorine and sodium hydroxide (p. 798). The ratio of H2 Cl2 NaOH is, of course, fixed by stoichiometry and this is an economic determinant since bulk transport of the byproduct hydrogen is expensive. To illustrate the scde of the problem the total world chlorine production capacity is about 38 million tonnes per year which corresponds to 105000 toimes of hydrogen (1.3 x I0 m ). Plants designed specifically for the electrolytic manufacture of hydrogen as the main product, use steel cells and aqueous potassium hydroxide as electrolyte. The cells may be operated at atmospheric pressure (Knowles cells) or at 30 atm (Lonza cells). 

Consistent with this, experiments using HS" labelled with radioactive (p. 661) show that acid hydrolysis of the 8203 produces elemental sulfur in which two-thirds of the activity is concentrated. Thiosulfates can also he made by boiling aqueous solutions of metal sulfites (or hydrogen sulfites) with elemental sulfur according to the stoichiometry... 

A similar observation was made in the ionic precipitation of lead(ll) iodide. When aqueous solutions of potassium iodide and sodium iodide were separately added to aqueous leadfll) nitrate, 12% of students believed that the ionic equation for the precipitation reactions was different in the two instances even though the stoichiometry of the two chemical reactions had no influence on the ionic equation. 

The first reported method for the direct phosphonomethylation of amino acids used phosphorous acid and formaldehyde (7). Typically, aqueous solutions of the amino acid, phosphorous acid, and concentrated (coned) hydrochloric acid were heated to reflux with excess aqueous formaldehyde or paraformaldehyde. The reaction proceeded equally well with either primary or secondary amines. However, with primary amines such as glycine, the yield of glyphosate was usually quite low, even at reduced temperature, and 1 1 1 stoichiometry. The resulting glyphosate acid (GLYH3) reacted faster than glycine, so the bis-phosphonomethyl adduct 2 always predominated. With excess phosphorous acid and formaldehyde, good isolated yields of this 2 1 adduct 2 have been obtained (8). 

We have studied stoichiometry of complex formation between DNA and PLL and found that the complexes formed in low-salt-buffer solutions are of a 1 1 charge ratio [92]. The same 1 1 stoichiometry was found experimentally for DNA complexed with other synthetic polycations of different nature in low-salt aqueous solutions [such as poly (diallyldimethylammonium chloride), poly(dimethyhmino)ethylene(dimethylimino)ethy-lene-l,4-dimethylphenylmethyl ene dichloride, andpoly(4-vinyl-A-methylpyridinium bromide)] [93]. 

The quantitative aspects of acid-base chemistry obey the principles Introduced earlier in this chapter. The common acid-base reactions that are important in general chemistry take place in aqueous solution, so acid-base stoichiometry uses molarities and volumes extensively. Example Illustrates the essential features of aqueous acid-base stoichiometry. 

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. 

Complex ions, also called coordination complexes, have well-defined stoichiometries and structural arrangements. Usually, the formula of a coordination complex is enclosed in brackets to show that the metal and all its ligands form a single structural entity. When an ionic coordination complex is isolated from aqueous solution, the product is composed of the complex ion and enough counter-ions to give a neutral salt. In the chemical formula, the counter-ions are shown outside the brackets. Examples include the sulfate salt of [Ni (NH3)g, ... 

Xenon trioxide is reduced in aqueous solution, in a thermal reaction by Pu(III) and photochemically by Np(V). The stoichiometry of the Pu(III) reduction is... 

An autocatalytic reaction is to be carried out in aqueous solution in two identical continuous stirred tank reactors operating in series. The reaction stoichiometry is... 

A Ca2+-specific fluorescent chemosensor 25 in aqueous buffer signals Ca2+ via a decrease in fluorescence intensity, whereas excess of Mg2+ ions has no effect on the emission [85]. This probe has limited solubility in aqueous solution after binding to Ca2+. A Zn2+ sensitive probe 26 showing different fluorescence responses depending on the complexation stoichiometry is described in [86],... 

The stoichiometry of Versatic 10 Ni extraction has been the subject of much investigation. Distribution data for the extraction of nickel from aqueous solution is consistent with the generalized equilibrium.266 267... 

BODIPY 530/550 C3 is insoluble in aqueous solution, but it may be dissolved in DMF or DMSO as a concentrated stock solution prior to addition of a small aliquot to a reaction. Coupling to amine-containing molecules may be done using the EDC/sulfo-NHS reaction as discussed in Chapter 3, Section 1.2 (Figure 9.29). However, modification of proteins with this fluorophore probably won t yield satisfactory results, since BODIPY fluorophores are easily quenched if substitutions on a molecule exceed a 1 1 stoichiometry. For labeling molecules which contain only one amine group, such as DNA probes modified at the 5 end to contain an amine (Chapter 27, Section 2.1), BODIPY 530/550 C3 will give intensely fluorescent derivatives. 

Lifetime of nitric oxide is an important parameter of its reactivity. Measurement of NO in intact tissue yielded a value in the order of 0.1 s [35] although preliminary estimates gave a much bigger lifetime. It has been accepted that the main reason for the rapid disappearance of NO in tissue is its reaction with dioxygen, which proceeds in aqueous solution with the following overall stoichiometry ... 

In a thorough study by Balia and coworkers, it was shown that in slightly acidic aqueous solution (25 °C, /jl = 1.0 KN03), the mechanism is very similar to that followed in aprotic media (36). Parallel measurement of the 02 consumption and quinone formation confirmed the following stoichiometry up to 35% conversion ... 

Job plots have established the stoichiometry of several iron(III)-3-hydroxy-2-methyl-4(l//)-pyridinone systems in aqueous solution.Stability constants have been determined for 1,2-dimethyl-, 1,2-diethyl-, and several other 3-hydroxy-4-pyridinonato-iron(III) complexes. " These data supplement and update the long-standing set of log / 3 values for... 

Most of the studies in aqueous solution have been devoted to interactions between homopolymers (5-10. In these systems the mean stoichiometry between interactive groups is close to 1 1. Only a few studies have been devoted to the behaviour of homopolymer/copolymer systems (11-14. Still a variation in copolymer composition leads to a modulation in the interpolymer interaction system. In a sense, inactive groups behave as structure defects. 

Using a dilute aqueous solution of the polymer in the absence of external salt, a molecular weight distribution was obtained, although it was perturbed by electrostatic exclusion. When CaCh was added, a salt exclusion corresponding to NaCl was formed, i.e., an exchange process occurred up to at least 40% of the stoichiometry, where in each case one Ca2+ expelled two Na+ (10). 

ID-ROESY studies performed on the complex between (+)-BrPh and /3-CD in solution did not allow one to explain the NOE effect observed on the protons of the maleate counteranion (70). X-ray crystallographic studies performed on the monocrystals obtained from a 1 1 aqueous solution of (+)-BrPh maleate and /3-CD (Fig. 8) provide a plausible explanation for the contradiction maintained in Ref. 70. In particular, as shown in Fig. 8, (+)-BrPh forms with /3-CD, at least in the solid state, not a 1 1 complex but a complex with 1 2 stoichiometry. In this complex the (+)-BrPh molecule is sandwiched between two molecules of /3-CD. The 4-bromophenyl moiety of (+)-BrPh enters the cavity of one of the /3-CD molecules, whereas the cavity of another /3-CD molecule is occupied by the maleate counteranion. Thus, X-ray crystallography may provide useful information on the supra-molecular structure of the selector-selectand complexes and in this way complement well ID-ROESY data. However, the aforementioned possible differences between the structure of the complexes in solution and in the solid phase must be considered. 

A mixed flow reactor is being used to determine the kinetics of a reaction whose stoichiometry is A R. For this purpose various flow rates of an aqueous solution of 100 mmol A/liter are fed to a 1-liter reactor, and for each run the outlet concentration of A is measured. Find a rate equation to represent the following data. Also assume that reactant alone affects the rate. 

Example 12-1 An aqueous solution containing lO ppm by weight of an organic contaminant of molecular weight 120 is to be removed by air oxidation in a l-cm-diameter falling film reactor at 25°C. The liquid flows at an average velocity of 10 Clll/sec and forms a film 1 mm thick on the wall, while the air at 1 atm flows at an average velocity of 2 cm/sec. The reaction in the liquid phase has the stoichiometry A + 2O2 products with a rate r K... 

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