Mixture of ions

Use of Coagulants Coagulants may also react with other constituents of the wastewater, particularly anions such as phosphate and sulfate, forming hydrolysis products containing various mixtures of ions. The chemistry of the reactions is extremely complex and highly dependent on pH and alkalinity. The presence of... 

Sometimes it is important to know under what conditions a precipitate will form. For example, if we are analyzing a mixture of ions, we may want to precipitate only one type of ion to separate it from the mixture. In Section 9.5, we saw how to predict the direction in which a reaction will take place by comparing the values of J, the reaction quotient, and K, the equilibrium constant. Exactly the same techniques can be used to decide whether a precipitate is likely to form when two electrolyte solutions are mixed. In this case, the equilibrium constant is the solubility product, Ksp, and the reaction quotient is denoted Qsp. Precipitation occurs when Qsp is greater than Ksp (Fig. 11.17). 

A mixture of ions in solution can be separated by adding an oppositely charged ion with which they form salts having very different solubilities. 

The concentration of ammonium ions is twice that of suifate ions. This is consistent with the 2 1 ratio of ammonium to suifate in the chemicai formuia. You shouid understand that when we describe this soiution as 0.0530 M (NH4)2 SO4 stating moies of salt per liter of soiution, we are describing a soiution that actuaiiy contains a mixture of ions, each with its own molarity. 

In other words, in tandem MS experiments two (MS/MS or MS2) or more (MS") sequential stages of mass analysis (which can be separated spatially or temporally) are used in order to examine selectively the decomposition of given ions, occurring out of the ion source, in a mixture of ions. Type and performances of the analyzers determine the kind of MS experiments that can be carried out. There are two main kinds of reactions that cause decomposition of ions occurring out of the source ... 

The source of the light seen with an electric discharge is the plasma formed by the electricity, which is a mixture of ions and electrons, and unionized atoms. If, for example, we look solely at nitrogen, which represents 78 per cent of the air, an electric discharge would form a plasma comprising N2"1", N+, electrons e, nitrogen radicals N, as well as unreacted N2. Incidentally, the formation of these ions explains how air may conduct electricity. 

This absorption is in fact due to the ions derived from l-methyl-3-phenylindane (the cyclic dimer of styrene) and its higher homologues (oligostyrenes with indanyl end groups). There can be no doubt that the ions formed at the end of the polymerisation of styrene belong to the same families of compounds (indanyl and various phenyl alkyl carbonium ions [7]). Our evidence showed that the 1-phenylethyl cation is absent from the ions formed from styrene by excess of acid its dimeric homologue, the l,3-diphenyl- -butyl cation, is a minor component of the ion mixture. We refer to this mixture of ions formed rapidly from styrene by excess acid, or at the end of a styrene polymerisation, as SD (styrene-derived) ions. 

In sulphuric acid the ion VII is formed as a minor constituent of the mixture of ions but we were unable to find it in experiments with perchloric acid in methylene dichloride [7]. None the less, it seems likely that minute amounts of it are formed at the end of the polymerisation when the perchloric acid is set free. 

Inert electrodes, such as silver, platinum, and carbon, are used solely to make electrical contact with the solution and only reflect the potential of the solution. They are used to measure the potential of solutions containing mixtures of ions which have a tendency to transfer electrons between them, e.g. ferric and ferrous ions ... 

It is incorrect to regard hard water as containing specific salts such as Ca(HC03)2, MgC03, MgS04, and CaCl2 because these are present in solution as mixtures of ions. The principal ions present in typical surface waters are... 

Separation of ions can be accomplished by selectively dissolving a mixture of precipitates, or by selectively precipitating a mixture of ions. The following problems illustrate this. 

DOUBLE SALT. A hydrated compound resulting from crystallization ol a mixture of ions in aqueous solution. Common examples arc the alums, made by ciystallizing from solution either potassium or ammonium sulfate and aluminum sulfate Rochelle salt (potassium sodium tartrate), made from a water solution of potassium acid tartrate treated with sodium carbonate and Mohr s salt (fertous ammonium sulfate), crystallized Iruin mixed solutions of ferrous sulfate and ammonium sulfate. 

Fig. 2. Simultaneous separation of a model mixture of ions using anion exchange column coated with sulfopolysaccha-ride. Column TSK-Gel IC-Anion SW (100X0.32 mm) dynamically modified with heparin eluent 1 mM copper sulfate flow rate 4.2 Jil / min sample volume 0.2 jal detection UV 200 nm. Reprinted with permission from [11].

A convenient method for separating a mixture of ions is to add a solution that will precipitate some of the ions but not others. The anions S042- and Cl-, for example, can be separated by addition of a solution of Ba(N03)2. Insoluble BaS04 precipitates, but Cl- remains in solution because BaCl2 is soluble. Similarly, the cations Ag+ and Zn2+ can be separated by addition of dilute HC1. Silver chloride, AgCl, precipitates, but Zn2+ stays in solution because ZnCl2 is soluble. 

The two mass action equilibria previously indicated have been used in conjunction with a modified form of the Shedlovsky conductance function to analyze the data in each of the cases listed in Table I. Where the data were precise enough, both K2 and K were calculated. As mentioned previously, the K s so evaluated are practically the same as those obtained for ion pairing in solutions of electrolytes in ammonia and amines. This is encouraging since it implies a fairly normal behavior (in the electrolyte sense) for dilute solutions of metals. Further support of the proposed mass action equilibria can be found in the conductance measurements of sodium in NH8 solutions with added salt. Bems, Lepoutre, Bockelman, and Patterson (4) assumed an additional equilibrium between sodium and chloride ions, associated to form NaCl, to compute the concentration of ionic species, monomers, and dimers when the common ion electrolyte is added. Calculated concentrations of conducting species are employed in the Onsager-Kim extension of the conductance theory for low-field conductance of a mixture of ions. Values of [Na]totai ranging from 5 X 10 4 to 6 X 10 2 and of the ratio of NaCl to [Na]totai ranging from zero to 28.5 are included in the calculations. 

The numerical results are consistent with the result of an experiment in which the ion cyclotron orbit sizes of a methane (CHi, ) and benzene (C6H6 ) mixture of ions were varied. In the control experiment, the two ions were excited by low amplitude consecutive RF burst pulses of varied time. The signal ratio was essentially constant over the range of orbits for which signals were detectable. In contrast, for a chirp from 10 kHz to 2 Mhz at 2.094 kHz/usee of varied amplitude, the abundance ratio of CH t/C6H6t decreased from about 90 to about 10 as the orbit size was increased, indicating loss of the lighter ion. 

Frequently, e.g. in the case of alkane thiol monolayers, the electrode is modified with a low-dielectric-constant layer. Film formation causes the Helmholtz layer to change from a mixture of ions and solvent with a high dielectric constant to an ion-free, often organic, layer with a low dielectric constant. The interfacial capacitance... 

The mass analyzer, which separates the mixture of ions that are generated during the ionization step by mlz in order to obtain a spectrum, is the heart of each mass spectrometer, and there are several different types with... 

In general, IPC is a useful technique as an alternative to IEC for the separation of ions or mixtures of ions and molecules. It does have some... 

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